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16-Bit, 750 kSPS, Unipolar/Bipolar Programmable Input PulSAR(R) ADC AD7612
FEATURES
Multiple pins/software programmable input ranges: 5 V, 10 V, 5 V, 10 V Pins or serial SPI(R)-compatible input ranges/mode selection Throughput 750 kSPS (warp mode) 600 kSPS (normal mode) 500 kSPS (impulse mode) INL: 0.75 LSB typical, 1.5 LSB maximum (23 ppm of FSR) 16-bit resolution with no missing codes SNR: 92 minimum (5 V) @ 2 kHz, 94 dB typical (10 V) @ 2 kHz THD: -107 dB typical iCMOSTM process technology 5 V internal reference: typical drift 3 ppm/C; TEMP output No pipeline delay (SAR architecture) Parallel (16- or 8-bit bus) and serial 5 V/3.3 V interface SPI-/QSPITM-/MICROWIRETM-/DSP-compatible Power dissipation: 190 mW @ 750 kSPS Pb-free, 48-lead LQFP and LFCSP (7 mm x 7 mm) packages
AGND AVDD PDREF PDBUF IN+ IN- SWITCHED CAP DAC REF
FUNCTIONAL BLOCK DIAGRAM
TEMP REFBUFIN REF REFGND VCC VEE DVDD DGND OVDD OGND
REF AMP
AD7612
SERIAL DATA PORT SERIAL CONFIGURATION 16 PORT
D[15:0] SER/PAR BYTESWAP
CNVST PD RESET
CLOCK CONTROL LOGIC AND CALIBRATION CIRCUITRY
PARALLEL INTERFACE
OB/2C BUSY RD CS
06265-001
WARP IMPULSE BIPOLAR TEN
Figure 1.
Table 1. 48-Lead 14-/16-/18-Bit PulSAR Selection
Type Pseudo Differential 100 kSPS to 250 kSPS AD7651 AD7660 AD7661 AD7663 AD7675 500 kSPS to 570 kSPS AD7650 AD7652 AD7664 AD7666 AD7665 AD7676 800 kSPS to 1000 kSPS AD7653 AD7667 >1000 kSPS
APPLICATIONS
Process control Medical instruments High speed data acquisition Digital signal processing Instrumentation Spectrum analysis ATE
True Bipolar True Differential 18-Bit, True Differential Multichannel/ Simultaneous
AD7612 AD7671 AD7677
AD7678
AD7679 AD7654 AD7655
AD7674
AD7621 AD7622 AD7623 AD7641 AD7643
GENERAL DESCRIPTION
The AD7612 is a 16-bit charge redistribution successive approximation register (SAR), architecture analog-to-digital converter (ADC) fabricated on Analog Devices, Inc.'s iCMOS high voltage process. The device is configured through hardware or via a dedicated write only serial configuration port for input range and operating mode. The AD7612 contains a high speed 16-bit sampling ADC, an internal conversion clock, an internal reference (and buffer), error correction circuits, and both serial and parallel system interface ports. A falling edge on CNVST samples the analog input on IN+ with respect to a ground sense, IN-. The AD7612 features four different analog input ranges and three different sampling modes: warp mode for the fastest throughput, normal mode for the fastest asynchronous throughput, and impulse mode where power consumption is scaled linearly with throughput. Operation is specified from -40C to +85C.
PRODUCT HIGHLIGHTS
1. 2. 3. 4. Programmable input range and mode selection. Pins or serial port for selecting input range/mode select. Fast throughput. In warp mode, the AD7612 is 750 kSPS. Superior Linearity. No missing 16-bit code. 1.5 LSB max INL. Internal Reference. 5 V internal reference with a typical drift of 3 ppm/C and an on-chip temperature sensor. Serial or Parallel Interface. Versatile parallel (16- or 8-bit bus) or 2-wire serial interface arrangement compatible with 3.3 V or 5 V logic.
5.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 (c)2006 Analog Devices, Inc. All rights reserved.
AD7612 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Product Highlights ........................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Timing Specifications .................................................................. 5 Absolute Maximum Ratings............................................................ 7 ESD Caution.................................................................................. 7 Pin Configuration and Function Descriptions............................. 8 Typical Performance Characteristics ........................................... 12 Terminology .................................................................................... 16 Theory of Operation ...................................................................... 17 Overview...................................................................................... 17 Converter Operation.................................................................. 17 Modes of Operation ................................................................... 18 Transfer Functions...................................................................... 18 Typical Connection Diagram ................................................... 19 Analog Inputs ............................................................................. 20 Driver Amplifier Choice ........................................................... 21 Voltage Reference Input/Output .............................................. 21 Power Supplies ............................................................................ 22 Conversion Control ................................................................... 23 Interfaces.......................................................................................... 24 Digital Interface.......................................................................... 24 Parallel Interface......................................................................... 24 Serial Interface ............................................................................ 25 Master Serial Interface............................................................... 25 Slave Serial Interface .................................................................. 27 Hardware Configuration ........................................................... 29 Software Configuration ............................................................. 29 Microprocessor Interfacing....................................................... 30 Application Information................................................................ 31 Layout Guidelines....................................................................... 31 Evaluating Performance ............................................................ 31 Outline Dimensions ....................................................................... 32 Ordering Guide .......................................................................... 32
REVISION HISTORY
10/06--Revision 0: Initial Version
Rev. 0 | Page 2 of 32
AD7612 SPECIFICATIONS
AVDD = DVDD = 5 V; OVDD = 2.7 V to 5.5 V; VCC = 15 V; VEE = -15 V; VREF = 5 V; all specifications TMIN to TMAX, unless otherwise noted. Table 2.
Parameter RESOLUTION ANALOG INPUT Voltage Range, VIN Conditions/Comments Min 16 -0.1 -0.1 -5.1 -10.1 -0.1 75 220 1 Typ Max Unit Bits V V V V V dB A
Analog Input CMRR Input Current Input Impedance THROUGHPUT SPEED Complete Cycle Throughput Rate Time Between Conversions Complete Cycle Throughput Rate Complete Cycle Throughput Rate DC ACCURACY Integral Linearity Error 3 No Missing Codes3 Differential Linearity Error3 Transition Noise Zero Error (Unipolar or Bipolar) Zero Error Temperature Drift Bipolar Full-Scale Error Unipolar Full-Scale Error Full-Scale Error Temperature Drift Power Supply Sensitivity AC ACCURACY Dynamic Range
VIN+ - VIN- = 0 V to 5 V VIN+ - VIN- = 0V to 10 V VIN+ - VIN- = 5 V VIN+ - VIN- = 10 V VIN- to AGND fIN = 100 kHz VIN = 5 V, 10 V @ 750 kSPS See Analog Inputs section In warp mode In warp mode In warp mode In normal mode In normal mode In impulse mode In impulse mode
+5.1 +10.1 +5.1 +10.1 +0.1
1
0 0 -1.5 16 -1 -35 1 -50 -70 0.75
1.33 750 2 1 1.67 600 2 500 +1.5 +1.5 0.55 +35 +50 +70 1 3
s kSPS ms s kSPS s kSPS LSB 4 Bits LSB LSB LSB ppm/C LSB LSB ppm/C LSB dB 5 dB dB dB dB dB dB dB dB dB MHz ns ps rms ns V ppm/C ppm/V ppm ms
AVDD = 5 V 5% VIN = 0 V to 5 V, fIN = 2 kHz, -60 dB VIN = 0 V to 10 V, 5 V, fIN = 2 kHz, -60 dB VIN = 10 V, fIN = 2 kHz, -60 dB VIN = 0 V to 5 V, 0 V to 10 V, fIN = 2 kHz VIN = 5 V, 10 V, fIN = 2 kHz VIN = 5 V, fIN = 2 kHz VIN = 0 V to 10 V, 5 V, fIN = 2 kHz VIN = 10 V, fIN = 2 kHz fIN = 2 kHz fIN = 2 kHz VIN = 0 V to 5 V 92.5
Signal-to-Noise Ratio Signal-to-(Noise + Distortion) (SINAD)
92
Total Harmonic Distortion Spurious-Free Dynamic Range -3 dB Input Bandwidth Aperture Delay Aperture Jitter Transient Response INTERNAL REFERENCE Output Voltage Temperature Drift Line Regulation Long-Term Drift Turn-On Settling Time
93.5 94 94.5 93 94 92.5 93 93.5 -107 107 45 2 5 500
Full-scale step PDREF = PDBUF = low REF @ 25C -40C to +85C AVDD = 5 V 5% 1000 hours CREF = 22 F
4.965
5.000 3 15 50 10
5.035
Rev. 0 | Page 3 of 32
AD7612
Parameter REFERENCE BUFFER REFBUFIN Input Voltage Range EXTERNAL REFERENCE Voltage Range Current Drain TEMPERATURE PIN Voltage Output Temperature Sensitivity Output Resistance DIGITAL INPUTS Logic Levels VIL VIH IIL IIH DIGITAL OUTPUTS Data Format Pipeline Delay 6 VOL VOH POWER SUPPLIES Specified Performance AVDD DVDD OVDD VCC VEE Operating Current 8 , 9 AVDD With Internal Reference With Internal Reference Disabled DVDD OVDD VCC VEE Power Dissipation With Internal Reference With Internal Reference Disabled In Power-Down Mode 10 TEMPERATURE RANGE 11 Specified Performance
1 2 3
Conditions/Comments PDREF = high PDREF = PDBUF = high REF 750 kSPS throughput @ 25C
Min 2.4 4.75
Typ 2.5 5 250 311 1 4.33
Max 2.6 AVDD + 0.1
Unit V V A mV mV/C k
-0.3 2.1 -1 -1 Parallel or serial 16-bit ISINK = 500 A ISOURCE = -500 A
+0.6 OVDD + 0.3 +1 +1
V V A A
0.4 OVDD - 0.6
V V
4.75 7 4.75 2.7 7 -15.75 @ 750 kSPS throughput
5 5 15 -15
5.25 5.25 5.25 15.75 0
V V V V V
VCC = 15 V, with internal reference buffer VCC = 15 V VEE = -15 V @ 750 kSPS throughput PDREF = PDBUF = low PDREF = PDBUF = high PD = high TMIN to TMAX -40
19.5 18 6.5 0.5 3 2.3 2 205 190 10 230 210
mA mA mA mA mA mA mA mW mW W C
+85
With VIN = 0 V to 5 V or 0 V to 10 V ranges, the input current is typically 70 A. In all input ranges, the input current scales with throughput. See the Analog Inputs section. All specified performance is guaranteed up to 750 kSPS throughout, however throughputs up to 900 kSPS can be used with some linearity performance degradation. Linearity is tested using endpoints, not best fit. All linearity is tested with an external 5 V reference. 4 LSB means least significant bit. All specifications in LSB do not include the error contributed by the reference. 5 All specifications in decibels are referred to a full-scale range input, FSR. Tested with an input signal at 0.5 dB below full-scale, unless otherwise specified. 6 Conversion results are available immediately after completed conversion. 7 4.75 V or VREF - 0.1 V, whichever is larger. 8 Tested in parallel reading mode. 9 With internal reference, PDREF = PDBUF = low; with internal reference disabled, PDREF = PDBUF = high. With internal reference buffer, PDBUF = low. 10 With all digital inputs forced to OVDD. 11 Consult sales for extended temperature range.
Rev. 0 | Page 4 of 32
AD7612
TIMING SPECIFICATIONS
AVDD = DVDD = 5 V; OVDD = 2.7 V to 5.5 V; VCC = 15 V; VEE = -15 V; VREF = 5 V; all specifications TMIN to TMAX, unless otherwise noted. Table 3.
Parameter CONVERSION AND RESET (See Figure 33 and Figure 34) Convert Pulse Width Time Between Conversions Warp Mode/Normal Mode/Impulse Mode1 CNVST Low to BUSY High Delay BUSY High All Modes (Except Master Serial Read After Convert) Warp Mode/Normal Mode/Impulse Mode Aperture Delay End of Conversion to BUSY Low Delay Conversion Time Warp Mode/Normal Mode/Impulse Mode Acquisition Time Warp Mode/Normal Mode/Impulse Mode RESET Pulse Width PARALLEL INTERFACE MODES (See Figure 35 and Figure 37) CNVST Low to DATA Valid Delay Warp Mode/Normal Mode/Impulse Mode DATA Valid to BUSY Low Delay Bus Access Request to DATA Valid Bus Relinquish Time MASTER SERIAL INTERFACE MODES2 (See Figure 39 and Figure 40) CS Low to SYNC Valid Delay CS Low to Internal SDCLK Valid Delay2 CS Low to SDOUT Delay CNVST Low to SYNC Delay, Read During Convert Warp Mode/Normal Mode/Impulse Mode SYNC Asserted to SDCLK First Edge Delay Internal SDCLK Period3 Internal SDCLK High3 Internal SDCLK Low3 SDOUT Valid Setup Time3 SDOUT Valid Hold Time3 SDCLK Last Edge to SYNC Delay3 CS High to SYNC HI-Z CS High to Internal SDCLK HI-Z CS High to SDOUT HI-Z BUSY High in Master Serial Read After Convert3 CNVST Low to SYNC Delay, Read After Convert Warp Mode/Normal Mode/Impulse Mode SYNC Deasserted to BUSY Low Delay Symbol t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 910/1160/1410 t11 t12 t13 t14 t15 t16 t17 65/315/560 t18 t19 t20 t21 t22 t23 t24 t25 t26 t27 t28 t29 t30 3 30 15 10 4 5 5 45 20 2 40 15 10 10 10 ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns 380 10 ns ns 2 10 950/1250/1450 Min 10 1.33/1.67/2 35 950/1250/1450 Typ Max Unit ns s ns ns ns ns ns
10 10 10 See Table 4 830/1070/1310 25
ns ns
Rev. 0 | Page 5 of 32
AD7612
Parameter SLAVE SERIAL/SERIAL CONFIGURATION INTERFACE MODES2 (See Figure 42, Figure 43, and Figure 45) External SDCLK, SCCLK Setup Time External SDCLK Active Edge to SDOUT Delay SDIN/SCIN Setup Time SDIN/SCIN Hold Time External SDCLK/SCCLK Period External SDCLK/SCCLK High External SDCLK/SCCLK Low
1 2
Symbol
Min
Typ
Max
Unit
t31 t32 t33 t34 t35 t36 t37
5 2 5 5 25 10 10
18
ns ns ns ns ns ns ns
In warp mode only, the time between conversions is 1 ms; otherwise, there is no required maximum time. In serial interface modes, the SDSYNC, SDSCLK, and SDOUT timings are defined with a maximum load CL of 10 pF; otherwise, the load is 60 pF maximum. 3 In serial master read during convert mode. See Table 4 for serial master read after convert mode.
Table 4. Serial Clock Timings in Master Read After Convert Mode
DIVSCLK[1] DIVSCLK[0] SYNC to SDCLK First Edge Delay Minimum Internal SDCLK Period Minimum Internal SDCLK Period Maximum Internal SDCLK High Minimum Internal SDCLK Low Minimum SDOUT Valid Setup Time Minimum SDOUT Valid Hold Time Minimum SDCLK Last Edge to SYNC Delay Minimum BUSY High Width Maximum Warp Mode Normal Mode Impulse Mode Symbol t18 t19 t19 t20 t21 t22 t23 t24 t28 0 0 3 30 45 15 10 4 5 5 1.65 1.9 2.15 0 1 20 60 90 30 25 20 8 7 2.35 2.6 2.85 1 0 20 120 180 60 55 20 35 35 3.75 4.00 4.25 1 1 20 240 360 120 115 20 90 90 6.53 6.78 7.03 Unit ns ns ns ns ns ns ns ns s s s
1.6mA
IOL
TO OUTPUT PIN
1.4V
CL 60pF
2V 0.8V
06265-003
500A
IOH
tDELAY
2V 0.8V
06265-002
tDELAY
2V 0.8V
NOTES 1. IN SERIAL INTERFACE MODES, THE SYNC, SCLK, AND SDOUT ARE DEFINED WITH A MAXIMUM LOAD CL OF 10pF; OTHERWISE, THE LOAD IS 60pF MAXIMUM.
Figure 2. Load Circuit for Digital Interface Timing, SDOUT, SYNC, and SCLK Outputs, CL = 10 pF
Figure 3. Voltage Reference Levels for Timing
Rev. 0 | Page 6 of 32
AD7612 ABSOLUTE MAXIMUM RATINGS
Table 5.
Parameter Analog Inputs/Outputs IN+1, IN-1 to AGND REF, REFBUFIN, TEMP, REFGND to AGND Ground Voltage Differences AGND, DGND, OGND Supply Voltages AVDD, DVDD, OVDD AVDD to DVDD, AVDD to OVDD DVDD to OVDD VCC to AGND, DGND VEE to GND Digital Inputs PDREF, PDBUF2 Internal Power Dissipation3 Internal Power Dissipation4 Junction Temperature Storage Temperature Range
1 2 3
Rating VEE - 0.3 V to VCC + 0.3 V AVDD + 0.3 V to AGND - 0.3 V 0.3 V -0.3 V to +7 V 7 V 7 V -0.3 V to +16.5 +0.3 V to -16.5 -0.3 V to OVDD + 0 .3 V 20 mA 700 mW 2.5 W 125C -65C to +125C
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ESD CAUTION
See the Analog Inputs section. See the Voltage Reference Input section. Specification is for the device in free air: 48-Lead LFQP; JA = 91C/W, JC = 30C/W. 4 Specification is for the device in free air: 48-Lead LFCSP; JA = 26C/W.
Rev. 0 | Page 7 of 32
AD7612 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
REFBUFIN REFGND PDBUF PDREF AGND AVDD TEMP VCC VEE
48 47 46 45 44 43 42 41 40 39 38 37 36 PIN 1 35 34 33
AGND 1 AVDD 2 AGND
3
REF
IN+
IN-
BIPOLAR CNVST PD RESET CS RD TEN BUSY D15/SCCS D14/SCCLK D13/SCIN D12/HW/SW
BYTESWAP 4 OB/2C 5 WARP 6 IMPULSE 7 SER/PAR 8 D0
9
AD7612
TOP VIEW (Not to Scale)
32 31 30 29 28 27 26 25
D1 10 D2/DIVSCLK[0] 11 D3/DIVSCLK[1] 12
13 14 15 16 17 18 19 20 21 22 23 24
D4/EXT/INT
OGND
OVDD
D6/INVSCLK
D5/INVSYNC
DGND
DVDD
D8/SDOUT
D7/RDC/SDIN
D10/SYNC
D11/RDERROR
D9/SDCLK
Figure 4. Pin Configuration
Table 6. Pin Function Descriptions
Pin No. 1, 3, 42 Mnemonic AGND Type1 P Description Analog Power Ground Pins. Ground reference point for all analog I/O. All analog I/O should be referenced to AGND and should be connected to the analog ground plane of the system. In addition, the AGND, DGND, and OGND voltages should be at the same potential. Analog Power Pins. Nominally 4.75 V to 5.25 V and decoupled with 10 F and 100 nF capacitors. Parallel Mode Selection (8-Bit/16-Bit). When high, the LSB is output on D[15:8] and the MSB is output on D[7:0]; when low, the LSB is output on D[7:0] and the MSB is output on D[15:8]. Straight Binary/Binary Twos Complement Output. When high, the digital output is straight binary. When low, the MSB is inverted resulting in a twos complement output from its internal shift register. Conversion Mode Selection. Used in conjunction with the IMPULSE input per the following: Conversion Mode WARP IMPULSE Normal Low Low Impulse Low High Warp High Low Normal High High See the Modes of Operation section for a more detailed description. Conversion Mode Selection. See the WARP pin description in the previous row of this table. See the Modes of Operation section for a more detailed description. Serial/Parallel Selection Input. When SER/PAR = low, the parallel mode is selected. When SER/PAR = high, the serial modes are selected. Some bits of the data bus are used as a serial port and the remaining data bits are high impedance outputs. Bit 0 and Bit 1 of the parallel port data output bus. These pins are always outputs regardless of the state of SER/PAR. In parallel mode, these outputs are used as Bit 2 and Bit 3 of the parallel port data output bus. Serial Data Division Clock Selection. In serial master read after convert mode (SER/PAR = high, EXT/INT = low, RDC/SDIN = low) these inputs can be used to slow down the internally generated serial data clock that clocks the data output. In other serial modes, these pins are high impedance outputs.
2, 44 4 5 6
AVDD BYTESWAP OB/2C WARP
P DI DI2 DI2
7 8
IMPULSE SER/PAR
DI2 DI
9, 10 11, 12
D[0:1] D[2:3] or DIVSCLK[0:1]
DO DI/O
Rev. 0 | Page 8 of 32
06265-004
AD7612
Pin No. 13 Mnemonic D4 or EXT/INT Type1 DI/O Description In parallel mode, this output is used as Bit 4 of the parallel port data output bus. Serial Data Clock Source Select. In serial mode, this input is used to select the internally generated (master) or external (slave) serial data clock for the AD7612 output data. When EXT/INT = low, master mode; the internal serial data clock is selected on SDCLK output. When EXT/INT = high, slave mode; the output data is synchronized to an external clock signal (gated by CS) connected to the SDCLK input. DI/O In parallel mode, this output is used as Bit 5 of the parallel port data output bus. Serial Data Invert Sync Select. In serial master mode (SER/PAR = high, EXT/INT = low). This input is used to select the active state of the SYNC signal. When INVSYNC = low, SYNC is active high. When INVSYNC = high, SYNC is active low. In parallel mode, this output is used as Bit 6 of the parallel port data output bus. In all serial modes, invert SDCLK/SCCLK select. This input is used to invert both SDCLK and SCCLK. When INVSCLK = low, the rising edge of SDCLK/SCCLK are used. When INVSCLK = high, the falling edge of SDCLK/SCCLK are used. In parallel mode, this output is used as Bit 7 of the parallel port data output bus. Serial Data Read During Convert. In serial master mode (SER/PAR = high, EXT/INT = low) RDC is used to select the read mode. Refer to the Master Serial Interface section. When RDC = low, the current result is read after conversion. Note the maximum throughput is not attainable in this mode. When RDC = high, the previous conversion result is read during the current conversion. Serial Data In. In serial slave mode (SER/PAR = high EXT/INT = high) SDIN can be used as a data input to daisy-chain the conversion results from two or more ADCs onto a single SDOUT line. The digital data level on SDIN is output on SDOUT with a delay of 16 SDCLK periods after the initiation of the read sequence. Input/Output Interface Digital Power Ground. Ground reference point for digital outputs. Should be connected to the system digital ground ideally at the same potential as AGND and DGND. Input/Output Interface Digital Power. Nominally at the same supply as the supply of the host interface 2.5 V, 3 V, or 5 V and decoupled with 10 F and 100 nF capacitors. Digital Power. Nominally at 4.75 V to 5.25 V and decoupled with 10 F and 100 nF capacitors. Can be supplied from AVDD. Digital Power Ground. Ground reference point for digital outputs. Should be connected to system digital ground ideally at the same potential as AGND and OGND. In parallel mode, this output is used as Bit 8 of the parallel port data output bus. Serial Data output. In all serial modes this pin is used as the serial data output synchronized to SDCLK. Conversion results are stored in an on-chip register. The AD7612 provides the conversion result, MSB first, from its internal shift register. The data format is determined by the logic level of OB/2C. When EXT/INT = low, (master mode) SDOUT is valid on both edges of SDCLK. When EXT/INT = high, (slave mode). When INVSCLK = low, SDOUT is updated on SDCLK rising edge. When INVSCLK = high, SDOUT is updated on SDCLK falling edge. In parallel mode, this output is used as Bit 9 of the parallel port data output bus. Serial Data Clock. In all serial modes, this pin is used as the serial data clock input or output, dependent on the logic state of the EXT/INT pin. The active edge where the data SDOUT is updated depends on the logic state of the INVSCLK pin. In parallel mode, this output is used as Bit 10 of the parallel port data output bus. Serial Data Frame Synchronization. In serial master mode (SER/PAR = high, EXT/INT= low), this output is used as a digital output frame synchronization for use with the internal data clock. When a read sequence is initiated and INVSYNC = low, SYNC is driven high and remains high while the SDOUT output is valid. When a read sequence is initiated and INVSYNC = high, SYNC is driven low and remains low while the SDOUT output is valid.
14
D5 or INVSYNC
15
D6 or INVSCLK
DI/O
16
D7 or RDC or
DI/O
SDIN
17 18 19 20 21
OGND OVDD DVDD DGND D8 or SDOUT
P P P P DO
22
D9 or SDCLK
DI/O
23
D10 or SYNC
DO
Rev. 0 | Page 9 of 32
AD7612
Pin No. 24 Mnemonic D11 or RDERROR Type1 DO Description In parallel mode, this output is used as Bit 11 of the parallel port data output bus. Serial Data Read Error. In serial slave mode (SER/PAR = high, EXT/INT = high), this output is used as an incomplete data read error flag. If a data read is started and not completed when the current conversion is complete, the current data is lost and RDERROR is pulsed high. In parallel mode, this output is used as Bit 12 of the parallel port data output bus. Serial Configuration Hardware/Software Select. In serial mode, this input is used to configure the AD7612 by hardware or software. See the Hardware Configuration section and Software Configuration section. When HW/SW = low, the AD7612 is configured through software using the serial configuration register. When HW/SW = high, the AD7612 is configured through dedicated hardware input pins. In parallel mode, this output is used as Bit 13 of the parallel port data output bus. Serial Configuration Data Input. In serial software configuration mode (SER/PAR = high, HW/SW = low) this input is used to serially write in, MSB first, the configuration data into the serial configuration register. The data on this input is latched with SCCLK. See the Software Configuration section. In parallel mode, this output is used as Bit 14 of the parallel port data output bus. Serial Configuration Clock. In serial software configuration mode (SER/PAR = high, HW/SW = low) this input is used to clock in the data on SCIN. The active edge where the data SCIN is updated depends on the logic state of the INVSCLK pin. See the Software Configuration section. In parallel mode, this output is used as Bit 15 of the parallel port data output bus. Serial Configuration Chip Select. In serial software configuration mode (SER/PAR = high, HW/SW = low) this input enables the serial configuration port. See the Software Configuration section. Busy Output. Transitions high when a conversion is started, and remains high until the conversion is complete and the data is latched into the on-chip shift register. The falling edge of BUSY can be used as a data ready clock signal. Note that in master read after convert mode (SER/PAR = high, EXT/INT = low, RDC = low) the busy time changes according to Table 4. Input Range Select. Used in conjunction with BIPOLAR per the following: Input Range BIPOLAR TEN 0 V to 5 V Low Low 0 V to 10 V Low High 5 V High Low 10 V High High Read Data. When CS and RD are both low, the interface parallel or serial output bus is enabled. Chip Select. When CS and RD are both low, the interface parallel or serial output bus is enabled. CS is also used to gate the external clock in slave serial mode (not used for serial programmable port). Reset Input. When high, reset the AD7612. Current conversion, if any, is aborted. The falling edge of RESET resets the data outputs to all zero's (with OB/2C = high) and clears the configuration register. See the Digital Interface section. If not used, this pin can be tied to OGND. Power-Down Input. When PD = high, power down the ADC. Power consumption is reduced and conversions are inhibited after the current one is completed. The digital interface remains active during power down. Conversion Start. A falling edge on CNVST puts the internal sample-and-hold into the hold state and initiates a conversion. Input Range Select. See description for Pin 30. Reference Input/Output. When PDREF/PDBUF = low, the internal reference and buffer are enabled, producing 5 V on this pin. When PDREF/PDBUF = high, the internal reference and buffer are disabled, allowing an externally supplied voltage reference up to AVDD volts. Decoupling with at least a 22 F is required with or without the internal reference and buffer. See the Reference Decoupling section. Reference Input Analog Ground. Connected to analog ground plane. Analog Input Ground Sense. Should be connected to the analog ground plane or to a remote sense ground. High Voltage Positive Supply. Normally +7 V to +15 V. High Voltage Negative Supply. Normally 0 V to -15 V (0 V in unipolar ranges).
25
D12 or HW/SW
DI/O
26
D13 or SCIN
DI/O
27
D14 or SCCLK
DI/O
28
D15 or SCCS BUSY
DI/O
29
DO
30
TEN
DI2
31 32 33
RD CS RESET
DI DI DI
34
PD
DI2
35 36 37
CNVST BIPOLAR REF
DI DI2 AI/O
38 39 40 41
REFGND IN- VCC VEE
AI AI P P
Rev. 0 | Page 10 of 32
AD7612
Pin No. 43 45 46 Mnemonic IN+ TEMP REFBUFIN Type1 AI AO AI Description Analog Input. Referenced to IN-. Temperature Sensor Analog Output. Reference Buffer Input. When using an external reference with the internal reference buffer (PDBUF = low, PDREF = high), applying 2.5 V on this pin produces 5 V on the REF pin. See the Voltage Reference Input section. Internal Reference Power-Down Input. When low, the internal reference is enabled. When high, the internal reference is powered down, and an external reference must be used. Internal Reference Buffer Power-Down Input. When low, the buffer is enabled (must be low when using internal reference). When high, the buffer is powered-down.
47
PDREF
DI
48
PDBUF
DI
AI = analog input; AI/O = bidirectional analog; AO = analog output; DI = digital input; DI/O = bidirectional digital; DO = digital output; P = power. In serial configuration mode (SER/PAR = high, HW/SW = low), this input is programmed with the serial configuration register and this pin is a don't care. See the Hardware Configuration section and Software Configuration section.
2
1
Rev. 0 | Page 11 of 32
AD7612 TYPICAL PERFORMANCE CHARACTERISTICS
AVDD = DVDD = 5 V; OVDD = 5 V; VCC = 15 V; VEE = -15 V; VREF = 5 V; TA = 25C.
1.5 1.5
1.0
1.0
0.5
0
DNL (LSB)
06265-005
INL (LSB)
0.5
0
-0.5 -0.5
-1.0
0
16384
32768 CODE
49152
65536
0
16384
32768 CODE
49152
65536
Figure 5. Integral Nonlinearity vs. Code
180 160 140
NUMBER OF UNITS
180
Figure 8. Differential Nonlinearity vs. Code
NEGATIVE DNL POSITIVE DNL
NEGATIVE INL POSITIVE INL
160 140
120 100 80 60 40 20
06265-006
NUMBER OF UNITS
120 100 80 60 40 20
06265-009 06265-010
0 -1.0
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1.0
0 -1.0
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1.0
INL DISTRIBUTION (LSB)
DNL DISTRIBUTION (LSB)
Figure 6. Integral Nonlinearity Distribution (239 Devices)
200k 180k 160k 140k 181942 = 0.55
Figure 9. Differential Nonlinearity Distribution (239 Devices)
140k 120k 100k 128400 130570 = 0.52
COUNTS
100k 80k 60k 40k 20k 7FFE 7FFF 8000 8001 8002 8003 8004 8005 8006
06265-007
COUNTS
120k
80k 60k 40k
47749 31321 0 0 15 93 0 0
20k 0 0 0 0 917 1232 1 0 0
0
7FFE 7FFF 8000 8001 8002 8003 8004 8005 8006 8007 CODE IN HEX
CODE IN HEX
Figure 7. Histogram of 261,120 Conversions of a DC Input at the Code Center
Figure 10. Histogram of 261,120 Conversions of a DC Input at the Code Transition
Rev. 0 | Page 12 of 32
06265-008
-1.5
-1.0
AD7612
0 -20
AMPLITUDE (dB of Full Scale)
fS = 750kSPS fIN = 19.99kHz
95.0
SNR SINAD
-40 -60 -80 -100 -120 -140 -160
SNR = 93.23dB THD = -107.5dB SFDR = 113.9dB SINAD = 93.1dB
SNR, SINAD (dB)
10V 5V 0V TO +10V 0V TO +5V
94.5
94.0
93.5
06265-011
0
125
250
375
-50
-40
-30
-20
-10
0
FREQUENCY (kHz)
INPUT LEVEL (dB)
Figure 11. FFT 20 kHz
96 SNR 94 SINAD 92
SNR, SINAD (dB)
Figure 14. SNR and SINAD vs. Input Level (Referred to Full Scale)
16.0 15.8 15.6
THD, HARMONICS (dB)
-70 SFDR 120 110 100 90
-80
88 86 84 82 80
15.2 15.0 14.8 14.6 14.4 100
-100
THD THIRD HARMONIC
70 60 50 40
-110
-120
SECOND HARMONIC 1 10 FREQUENCY (kHz)
30
06265-015 06265-016
1
10 FREQUENCY (kHz)
06265-012
-130
20 100
Figure 12. SNR, SINAD, and ENOB vs. Frequency
96
10V 5V 0V TO +10V 0V TO +5V
Figure 15. THD, Harmonics, and SFDR vs. Frequency
96
10V 5V 0V TO +10V 0V TO +5V
95
95
94
SINAD (dB) SNR (dB)
94
93
93
92
92
91
91
-35
-15
5
25
45
65
85
105
125
06265-013
90 -55
90 -55
-35
-15
5
25
45
65
85
105
125
TEMPERATURE (C)
TEMPERATURE (C)
Figure 13. SNR vs. Temperature
Figure 16. SINAD vs. Temperature
Rev. 0 | Page 13 of 32
SFDR (dB)
ENOB
ENOB (Bits)
90
15.4
-90
80
06265-014
-180
93.0 -60
AD7612
-96 -98 -100 -102 -104
10V 5V 0V TO +10V 0V TO +5V
124 122 120 118
SFDR (dB)
0V TO +10V 5V 10V 0V TO +5V
THD (dB)
-106 -108 -110 -112 -114 -116 -118 -35 -15 5 25 45 65 85 105 125
06265-017
116 114 112 110 108
06265-020 06265-022 06265-021
-120 -55
106 -55
-35
-15
5
25
45
65
85
105
125
TEMPERATURE (C)
TEMPERATURE (C)
Figure 17. THD vs. Temperature
5 5.002 5.001 POSITIVE FULL SCALE ERROR ZERO ERROR NEGATIVE FULL SCALE ERROR 5.000
Figure 20. SFDR vs. Temperature (Excludes Harmonics)
ZERO ERROR, FULL SCALE ERROR (LSB)
4 3 2 1 0 -1 -2 -3 -4 -35 -15 5 25 45 65 85 105 125
06265-018
VREF (V)
4.999 4.998 4.997 4.996 4.995 -55
-5 -55
-35
-15
5
25
45
65
85
105
125
TEMPERATURE (C)
TEMPERATURE (C)
Figure 18. Zero Error, Positive and Negative Full Scale vs. Temperature
60
Figure 21. Typical Reference Voltage Output vs. Temperature (3 Devices)
100000 10000
50
OPERATING CURRENTS (A)
1000 100 10 1 0.1 0.01 0.001 10 PDREF = PDBUF = HIGH 100 1000 10000 100000 1000000 AVDD, WARP/NORMAL DVDD, ALL MODES AVDD, IMPULSE VCC +15V, VEE -15V, ALL MODES OVDD, ALL MODES
NUMBER OF UNITS
40
30
20
10
0
1
2
3
4
5
6
7
8
06265-019
0
REFERENCE DRIFT (ppm/C)
SAMPLING RATE (SPS)
Figure 19. Reference Voltage Temperature Coefficient Distribution (247 Devices)
Figure 22. Operating Currents vs. Sample Rate
Rev. 0 | Page 14 of 32
AD7612
700
50
POWER-DOWN OPERATING CURRENTS (nA)
PD = PDBUF = PDREF = HIGH
45 40 35
OVDD = 2.7V @ 85C OVDD = 2.7V @ 25C
600 500
t12 DELAY (ns)
400 300 200 100 0 -55
30 25 20 OVDD = 5V @ 25C 15 10 5 0 OVDD = 5V @ 85C
VEE, -15V VCC, +15V DVDD OVDD AVDD
TEMPERATURE (C)
CL (pF)
Figure 23. Power-Down Operating Currents vs. Temperature
Figure 24. Typical Delay vs. Load Capacitance CL
Rev. 0 | Page 15 of 32
06265-024
-35
-15
5
25
45
65
85
105
06265-023
0
50
100
150
200
AD7612 TERMINOLOGY
Least Significant Bit (LSB) The least significant bit, or LSB, is the smallest increment that can be represented by a converter. For an analog-to-digital converter with N bits of resolution, the LSB expressed in volts is
LSB(V ) = VINp-p 2N
Total Harmonic Distortion (THD) THD is the ratio of the rms sum of the first five harmonic components to the rms value of a full-scale input signal and is expressed in decibels. Signal-to-(Noise + Distortion) Ratio (SINAD) SINAD is the ratio of the rms value of the actual input signal to the rms sum of all other spectral components below the Nyquist frequency, including harmonics but excluding dc. The value for SINAD is expressed in decibels. Spurious-Free Dynamic Range (SFDR) The difference, in decibels (dB), between the rms amplitude of the input signal and the peak spurious signal. Effective Number of Bits (ENOB) ENOB is a measurement of the resolution with a sine wave input. It is related to SINAD and is expressed in bits by ENOB = [(SINADdB - 1.76)/6.02] Aperture Delay Aperture delay is a measure of the acquisition performance measured from the falling edge of the CNVST input to when the input signal is held for a conversion. Transient Response The time required for the AD7612 to achieve its rated accuracy after a full-scale step function is applied to its input. Reference Voltage Temperature Coefficient Reference voltage temperature coefficient is derived from the typical shift of output voltage at 25C on a sample of parts at the maximum and minimum reference output voltage (VREF) measured at TMIN, T(25C), and TMAX. It is expressed in ppm/C as
TCVREF ( ppm/C ) = VREF ( Max ) - VREF ( Min) VREF ( 25C ) x ( TMAX - TMIN ) x106
Integral Nonlinearity Error (INL) Linearity error refers to the deviation of each individual code from a line drawn from negative full-scale through positive fullscale. The point used as negative full-scale occurs a 1/2 LSB before the first code transition. Positive full-scale is defined as a level 11/2 LSBs beyond the last code transition. The deviation is measured from the middle of each code to the true straight line. Differential Nonlinearity Error (DNL) In an ideal ADC, code transitions are 1 LSB apart. Differential nonlinearity is the maximum deviation from this ideal value. It is often specified in terms of resolution for which no missing codes are guaranteed. Bipolar Zero Error The difference between the ideal midscale input voltage (0 V) and the actual voltage producing the midscale output code. Unipolar Offset Error The first transition should occur at a level 1/2 LSB above analog ground. The unipolar offset error is the deviation of the actual transition from that point. Full-Scale Error The last transition (from 111...10 to 111...11) should occur for an analog voltage 11/2 LSB below the nominal full-scale. The fullscale error is the deviation in LSB (or % of full-scale range) of the actual level of the last transition from the ideal level and includes the effect of the offset error. Closely related is the gain error (also in LSB or % of full-scale range), which does not include the effects of the offset error. Dynamic Range Dynamic range is the ratio of the rms value of the full-scale to the rms noise measured for an input typically at -60 dB. The value for dynamic range is expressed in decibels. Signal-to-Noise Ratio (SNR) SNR is the ratio of the rms value of the actual input signal to the rms sum of all other spectral components below the Nyquist frequency, excluding harmonics and dc. The value for SNR is expressed in decibels.
where: VREF (Max) = maximum VREF at TMIN, T(25C), or TMAX. VREF (Min) = minimum VREF at TMIN, T(25C), or TMAX. VREF (25C) = VREF at 25C. TMAX = +85C. TMIN = -40C.
Rev. 0 | Page 16 of 32
AD7612 THEORY OF OPERATION
IN+ REF REFGND MSB 32,768C 16,384C 4C 2C C C BUSY COMP IN- 65,536C SWB CNVST CONTROL LOGIC OUTPUT CODE
06265-025
LSB
SWA
SWITCHES CONTROL
Figure 25. ADC Simplified Schematic
OVERVIEW
The AD7612 is a very fast, low power, precise, 16-bit analog-todigital converter (ADC) using successive approximation capacitive digital-to-analog (CDAC) architecture. The AD7612 can be configured at any time for one of four input ranges and conversion mode with inputs in parallel and serial hardware modes or by a dedicated write only, SPI-compatible interface via a configuration register in serial software mode. The AD7612 uses Analog Device's patented iCMOS high voltage process to accommodate 0 to 5 V, 0 to 10 V, 5 V, and 10 V input ranges without the use of conventional thin films. Only one acquisition cycle, t8, is required for the inputs to latch to the correct configuration. Resetting or power cycling is not required for reconfiguring the ADC. The AD7612 features different modes to optimize performance according to the applications. It is capable of converting 750,000 samples per second (750 kSPS) in warp mode, 600 kSPS in normal mode, and 500 kSPS in impulse mode. The AD7612 provides the user with an on-chip track-and-hold, successive approximation ADC that does not exhibit any pipeline or latency, making it ideal for multiple multiplexed channel applications. For unipolar input ranges, the AD7612 typically requires three supplies; VCC, AVDD (which can supply DVDD), and OVDD which can be interfaced to either 5 V, 3.3 V, or 2.5 V digital logic. For bipolar input ranges, the AD7612 requires the use of the additional VEE supply. The device is housed in Pb-free, 48-lead LQFP or tiny LFCSP 7 mm x 7 mm packages that combine space savings with flexibility. In addition, the AD7612 can be configured as either a parallel or serial SPI-compatible interface.
CONVERTER OPERATION
The AD7612 is a successive approximation ADC based on a charge redistribution DAC. Figure 25 shows the simplified schematic of the ADC. The CDAC consists of two identical arrays of 16 binary weighted capacitors, which are connected to the two comparator inputs. During the acquisition phase, terminals of the array tied to the comparator's input are connected to AGND via SW+ and SW-. All independent switches are connected to the analog inputs. Thus, the capacitor arrays are used as sampling capacitors and acquire the analog signal on IN+ and IN- inputs. A conversion phase is initiated once the acquisition phase is complete and the CNVST input goes low. When the conversion phase begins, SW+ and SW- are opened first. The two capacitor arrays are then disconnected from the inputs and connected to the REFGND input. Therefore, the differential voltage between the inputs (IN+ and IN-) captured at the end of the acquisition phase is applied to the comparator inputs, causing the comparator to become unbalanced. By switching each element of the capacitor array between REFGND and REF, the comparator input varies by binary weighted voltage steps (VREF/2, VREF/4 through VREF/ 65536). The control logic toggles these switches, starting with the MSB first, in order to bring the comparator back into a balanced condition. After the completion of this process, the control logic generates the ADC output code and brings the BUSY output low.
Rev. 0 | Page 17 of 32
AD7612
MODES OF OPERATION
The AD7612 features three modes of operation: warp, normal, and impulse. Each of these modes is more suitable to specific applications. The mode is configured with the input pins, WARP and IMPULSE, or via the configuration register. See Table 6 for the pin details and the Hardware Configuration section and Software Configuration section for programming the mode selection with either pins or configuration register. Note that when using the configuration register, the WARP and IMPULSE inputs are don't cares and should be tied to either high or low. Warp Mode Setting WARP = high and IMPULSE = low allow the fastest conversion rate up to 750 kSPS. However, in this mode, the full specified accuracy is guaranteed only when the time between conversions does not exceed 1 ms. If the time between two consecutive conversions is longer than 1 ms (after power-up), the first conversion result should be ignored since in warp mode, the ADC performs a background calibration during the SAR conversion process. This calibration can drift if the time between conversions exceeds 1 ms thus causing the first conversion to appear offset. This mode makes the AD7612 ideal for applications where both high accuracy and fast sample rate are required. In addition, the AD7612 can run up to 900 kSPS throughput with some performance degradation, mainly dc linearity.
Impulse Mode
Setting WARP = low and IMPULSE = high uses the lowest power dissipation mode and allows power saving between conversions. The maximum throughput in this mode is 500 kSPS and in this mode, the ADC powers down circuits after conversion making the AD7612 ideal for battery-powered applications.
TRANSFER FUNCTIONS
Using the OB/2C digital input or via the configuration register, the AD7612 offers two output codings: straight binary and twos complement. See Figure 26 and Table 7 for the ideal transfer characteristic and digital output codes for the different analog input ranges, VIN. Note that when using the configuration register, the OB/2C input is a don't care and should be tied to either high or low.
ADC CODE (Straight Binary)
111...111 111...110 111...101
-FSR + 0.5 LSB
+FSR - 1.5 LSB ANALOG INPUT
Setting WARP = IMPULSE = low or WARP = IMPULSE = high allows the fastest mode (600 kSPS) without any limitation on time between conversions. This mode makes the AD7612 ideal for asynchronous applications such as data acquisition systems, where both high accuracy and fast sample rate are required.
Figure 26. ADC Ideal Transfer Function
Table 7. Output Codes and Ideal Input Voltages
Description FSR - 1 LSB FSR - 2 LSB Midscale + 1 LSB Midscale Midscale - 1 LSB -FSR + 1 LSB -FSR
1 2
VIN = 5 V 4.999924 V 4.999847 V 2.500076 V 2.5 V 2.499924 V 76.3 V 0V
VIN = 10 V 9.999847 V 9.999695 V 5.000153 V 5.000000 V 4.999847 V 152.6 V 0V
VREF = 5 V VIN = 5 V +4.999847 V +4.999695 V +152.6 V 0V -152.6 V -4.999847 V -5 V
VIN = 10 V +9.999695 V +9.999390 V +305.2 V 0V -305.2 V -9.999695 V -10 V
Digital Output Code Straight Binary Twos Complement 0xFFFF 1 0x7FFF1 0xFFFE 0x7FFE 0x8001 0x0001 0x8000 0x0000 0x7FFF 0xFFFF 0x0001 0x8001 0x0000 2 0x80002
This is also the code for overrange analog input (VIN+ - VIN- above VREF - VREFGND). This is also the code for overrange analog input (VIN+ - VIN- below VREF - VREFGND).
Rev. 0 | Page 18 of 32
06265-026
Normal Mode
000...010 000...001 000...000 -FSR
-FSR + 1 LSB
+FSR - 1 LSB
AD7612
TYPICAL CONNECTION DIAGRAM
Figure 27 shows a typical connection diagram for the AD7612 using the internal reference, serial data interface, and serial configuration port. Different circuitry from that shown in Figure 27 is optional and is discussed in the following sections.
DIGITAL SUPPLY (5V)
NOTE 5
ANALOG SUPPLY (5V) 10F 100nF 10F 100nF 100nF 10F
DIGITAL INTERFACE SUPPLY (2.5V, 3.3V, or 5V)
AVDD +7V TO +15.75V SUPPLY 10F 100nF VCC
AGND
DGND
DVDD
OVDD
OGND BUSY SDCLK MICROCONVERTER/ MICROPROCESSOR/ DSP SERIAL PORT 1 SERIAL PORT 2
10F -7V TO -15.75V SUPPLY
NOTE 6
100nF VEE REF
NOTE 3
SDOUT SCCLK SCIN SCCS
NOTE 7
NOTE 4
CREF 22F
100nF
REFBUFIN REFGND CNVST
D
AD7612
NOTE 2
OB/2C SER/PAR OVDD
ANALOG INPUT +
U1 CC 2.7nF
IN+
HW/SW BIPOLAR TEN WARP CLOCK
ANALOG INPUT-
NOTE 1
IN-
NOTE 3
IMPULSE PD RD CS RESET
PDREF PDBUF
Figure 27. Typical Connection Diagram Shown with Serial Interface and Serial Programmable Port
Rev. 0 | Page 19 of 32
06265-027
NOTES 1. SEE ANALOG INPUT SECTION. ANALOG INPUT(-) IS REFERENCED TO AGND 0.1V. 2. THE AD8021 IS RECOMMENDED. SEE DRIVER AMPLIFIER CHOICE SECTION. 3. THE CONFIGURATION SHOWN IS USING THE INTERNAL REFERENCE. SEE VOLTAGE REFERENCE INPUT SECTION. 4. A 22F CERAMIC CAPACITOR (X5R, 1206 SIZE) IS RECOMMENDED (FOR EXAMPLE, PANASONIC ECJ4YB1A226M). SEE VOLTAGE REFERENCE INPUT SECTION. 5. OPTION, SEE POWER SUPPLY SECTION. 6. THE VCC AND VEE SUPPLIES SHOULD BE VCC = [VIN(MAX) +2V] and VEE = [VIN(MIN) -2V] FOR BIPOLAR INPUT RANGES. FOR UNIPOLAR INPUT RANGES, VEE CAN BE 0V. SEE POWER SUPPLY SECTION. 7. OPTIONAL LOW JITTER CNVST, SEE CONVERSION CONTROL SECTION.
AD7612
ANALOG INPUTS
Input Range Selection
In parallel mode and serial hardware mode, the input range is selected by using the BIPOLAR (bipolar) and TEN (10 Volt range) inputs. See Table 6 for pin details and the Hardware Configuration section and Software Configuration section for programming the mode selection with either pins or configuration register. Note that when using the configuration register, the BIPOLAR and TEN inputs are don't cares and should be tied to either high or low. For instance, by using IN- to sense a remote signal ground, ground potential differences between the sensor and the local ADC ground are eliminated.
100 90 80 70
CMRR (dB)
60 50 40 30 20 10 1 10 100 FREQUENCY (kHz) 1000 10000
06265-029
Input Structure
Figure 28 shows an equivalent circuit for the input structure of the AD7612.
0 TO 5V RANGE ONLY VCC D1 IN+ OR IN- CPIN VEE AGND D2 D4 AVDD D3 CIN
0 RIN
Figure 29. Analog Input CMRR vs. Frequency
Figure 28. AD7612 Simplified Analog Input
The four diodes, D1 to D4, provide ESD protection for the analog inputs, IN+ and IN-. Care must be taken to ensure that the analog input signal never exceeds the supply rails by more than 0.3 V, because this causes the diodes to become forward-biased and to start conducting current. These diodes can handle a forwardbiased current of 120 mA maximum. For instance, these conditions could eventually occur when the input buffer's U1 supplies are different from AVDD, VCC, and VEE. In such a case, an input buffer with a short-circuit current limitation can be used to protect the part although most op amps' short circuit current is <100 mA. Note that D3 and D4 are only used in the 0 V to 5 V range to allow for additional protection in applications that are switching from the higher voltage ranges. This analog input structure allows the sampling of the differential signal between IN+ and IN-. By using this differential input, small signals common to both inputs are rejected as shown in Figure 29, which represents the typical CMRR over frequency.
During the acquisition phase for ac signals, the impedance of the analog inputs, IN+ and IN-, can be modeled as a parallel combination of Capacitor CPIN and the network formed by the series connection of RIN and CIN. CPIN is primarily the pin capacitance. RIN is typically 70 and is a lumped component comprised of serial resistors and the on resistance of the switches. CIN is primarily the ADC sampling capacitor and depending on the input range selected is typically 48 pF in the 0 V to 5 V range, typically 24 pF in the 0 V to 10 V and 5 V ranges and typically 12 pF in the 10 V range. During the conversion phase, when the switches are opened, the input impedance is limited to CPIN. Since the input impedance of the AD7612 is very high, it can be directly driven by a low impedance source without gain error. To further improve the noise filtering achieved by the AD7612 analog input circuit, an external, one-pole RC filter between the amplifier's outputs and the ADC analog inputs can be used, as shown in Figure 27. However, large source impedances significantly affect the ac performance, especially total harmonic distortion (THD). The maximum source impedance depends on the amount of THD that can be tolerated. The THD degrades as a function of the source impedance and the maximum input frequency.
Rev. 0 | Page 20 of 32
06265-028
AD7612
DRIVER AMPLIFIER CHOICE
Although the AD7612 is easy to drive, the driver amplifier must meet the following requirements: * For multichannel, multiplexed applications, the driver amplifier and the AD7612 analog input circuit must be able to settle for a full-scale step of the capacitor array at a 16-bit level (0.0015%). For the amplifier, settling at 0.1% to 0.01% is more commonly specified. This differs significantly from the settling time at a 16-bit level and should be verified prior to driver selection. The AD8021 op amp combines ultra-low noise and high gain bandwidth and meets this settling time requirement even when used with gains of up to 13. The noise generated by the driver amplifier needs to be kept as low as possible to preserve the SNR and transition noise performance of the AD7612. The noise coming from the driver is filtered by the external 1-pole low-pass filter as shown in Figure 27. The SNR degradation due to the amplifier is
VNADC = 20 log VNADC 2 + f -3dB (NeN )2 2
The AD8021 meets these requirements and is appropriate for almost all applications. The AD8021 needs a 10 pF external compensation capacitor that should have good linearity as an NPO ceramic or mica type. Moreover, the use of a noninverting +1 gain arrangement is recommended and helps to obtain the best signal-to-noise ratio. The AD8022 can also be used when a dual version is needed and a gain of 1 is present. The AD829 is an alternative in applications where high frequency (above 100 kHz) performance is not required. In applications with a gain of 1, an 82 pF compensation capacitor is required. The AD8610 is an option when low bias current is needed in low frequency applications. Since the AD7612 uses a large geometry, high voltage input switch, the best linearity performance is obtained when using the amplifier at its maximum full power bandwidth. Gaining the amplifier to make use of the more dynamic range of the ADC results in increased linearity errors. For applications requiring more resolution, the use of an additional amplifier with gain should precede a unity follower driving the AD7612. See Table 8 for a list of recommended op amps. Table 8. Recommended Driver Amplifiers
Amplifier ADA4841-x AD829 AD8021 AD8022 AD8610/AD8620 Typical Application 12 V supply, very low noise, low distortion, low power, low frequency 15 V supplies, very low noise, low frequency 12 V supplies, very low noise, high frequency 12 V supplies, very low noise, high frequency, dual 13 V supplies, low bias current, low frequency, single/dual
*
SNRLOSS
where: VNADC is the noise of the ADC, which is:
VINp-p 2 VNADC = 2 SNR 10
20
f-3dB is the cutoff frequency of the input filter (3.9 MHz). N is the noise factor of the amplifier (+1 in buffer configuration). eN is the equivalent input voltage noise density of the op amp, in nV/Hz. * The driver needs to have a THD performance suitable to that of the AD7612. Figure 15 shows the THD vs. frequency that the driver should exceed.
VOLTAGE REFERENCE INPUT/OUTPUT
The AD7612 allows the choice of either a very low temperature drift internal voltage reference, an external reference or an external buffered reference. The internal reference of the AD7612 provides excellent performance and can be used in almost all applications. However, the linearity performance is guaranteed only with an external reference.
Rev. 0 | Page 21 of 32
AD7612
Internal Reference (REF = 5 V) (PDREF = Low, PDBUF = Low)
To use the internal reference, the PDREF and PDBUF inputs must be low. This enables the on-chip band gap reference, buffer, and TEMP sensor resulting in a 5.00 V reference on the REF pin. The internal reference is temperature-compensated to 5.000 V 35 mV. The reference is trimmed to provide a typical drift of 3 ppm/C. This typical drift characteristic is shown in Figure 19.
Temperature Sensor
The TEMP pin measures the temperature of the AD7612. To improve the calibration accuracy over the temperature range, the output of the TEMP pin is applied to one of the inputs of the analog switch (such as ADG779), and the ADC itself is used to measure its own temperature. This configuration is shown in Figure 30.
ADG779
ANALOG INPUT (UNIPOLAR) CC TEMP
AD8021
IN+ TEMPERATURE SENSOR
To use an external reference with the internal buffer, PDREF should be high and PDBUF should be low. This powers down the internal reference and allows the 2.5 V reference to be applied to REFBUFIN producing 5 V on the REF pin. The internal reference buffer is useful in multiconverter applications since a buffer is typically required in these applications.
AD7612
Figure 30. Use of the Temperature Sensor
POWER SUPPLIES
The AD7612 uses five sets of power supply pins: * * * * * AVDD: analog 5 V core supply VCC: analog high voltage positive supply VEE: high voltage negative supply DVDD: digital 5 V core supply OVDD: digital input/output interface supply
External 5 V Reference (PDREF = High, PDBUF = High)
To use an external reference directly on the REF pin, PDREF and PDBUF should both be high. PDREF and PDBUF power down the internal reference and the internal reference buffer, respectively. For improved drift performance, an external reference such as the ADR445 or ADR435 is recommended.
Reference Decoupling
Whether using an internal or external reference, the AD7612 voltage reference input (REF) has a dynamic input impedance; therefore, it should be driven by a low impedance source with efficient decoupling between the REF and REFGND inputs. This decoupling depends on the choice of the voltage reference, but usually consists of a low ESR capacitor connected to REF and REFGND with minimum parasitic inductance. A 22 F (X5R, 1206 size) ceramic chip capacitor (or 47 F tantalum capacitor) is appropriate when using either the internal reference or the ADR445/ADR435 external reference. The placement of the reference decoupling is also important to the performance of the AD7612. The decoupling capacitor should be mounted on the same side as the ADC right at the REF pin with a thick PCB trace. The REFGND should also connect to the reference decoupling capacitor with the shortest distance and to the analog ground plane with several vias. For applications that use multiple AD7612 or other PulSAR devices, it is more effective to use the internal reference buffer to buffer the external 2.5 V reference voltage. The voltage reference temperature coefficient (TC) directly impacts full scale; therefore, in applications where full-scale accuracy matters, care must be taken with the TC. For instance, a 15 ppm/C TC of the reference changes full-scale by 1 LSB/C.
Core Supplies
The AVDD and DVDD supply the AD7612 analog and digital cores respectively. Sufficient decoupling of these supplies is required consisting of at least a 10 F capacitor and 100 nF on each supply. The 100 nF capacitors should be placed as close as possible to the AD7612. To reduce the number of supplies needed, the DVDD can be supplied through a simple RC filter from the analog supply, as shown in Figure 27.
High Voltage Supplies
The high voltage bipolar supplies, VCC and VEE are required and must be at least 2 V larger than the maximum input, VIN. For example, if using the bipolar 10 V range, the supplies should be 12 V minimum. Sufficient decoupling of these supplies is also required consisting of at least a 10 F capacitor and 100 nF on each supply. For unipolar operation, the VEE supply can be grounded with some slight THD performance degradation.
Digital Output Supply
The OVDD supplies the digital outputs and allows direct interface with any logic working between 2.3 V and 5.25 V. OVDD should be set to the same level as the system interface. Sufficient decoupling is required consisting of at least a 10 F capacitor and 100 nF with the 100 nF placed as close as possible to the AD7612.
Rev. 0 | Page 22 of 32
06265-030
External 2.5 V Reference and Internal Buffer (REF = 5 V) (PDREF = High, PDBUF = Low)
AD7612
Power Sequencing
The AD7612 is independent of power supply sequencing and is very insensitive to power supply variations on AVDD over a wide frequency range as shown in Figure 31.
80 75 70 65
PSRR (dB)
Power Down
Setting PD = high powers down the AD7612, thus reducing supply currents to their minimums as shown in Figure 23. When the ADC is in power down, the current conversion (if any) is completed and the digital bus remains active. To further reduce the digital supply currents, drive the inputs to OVDD or OGND. Power down can also be programmed with the configuration register. See the Software Configuration section for details. Note that when using the configuration register, the PD input is a don't care and should be tied to either high or low.
EXT REF INT REF
60 55 50 45 40 35 30 1 10 100 FREQUENCY (kHz) 1000 10000
CONVERSION CONTROL
The AD7612 is controlled by the CNVST input. A falling edge on CNVST is all that is necessary to initiate a conversion. Detailed timing diagrams of the conversion process are shown in Figure 33. Once initiated, it cannot be restarted or aborted, even by the power-down input, PD, until the conversion is complete. The CNVST signal operates independently of CS and RD signals.
t2 t1
CNVST
Figure 31. AVDD PSRR vs. Frequency
Power Dissipation vs. Throughput
In impulse mode, the AD7612 automatically reduces its power consumption at the end of each conversion phase. During the acquisition phase, the operating currents are very low, which allows a significant power savings when the conversion rate is reduced (see Figure 32). This feature makes the AD7612 ideal for very low power, battery-operated applications. It should be noted that the digital interface remains active even during the acquisition phase. To reduce the operating digital supply currents even further, drive the digital inputs close to the power rails (that is, OVDD and OGND).
1000 PDREF = PDBUF = HIGH
06265-031
BUSY
t4 t3 t5 t6
CONVERT ACQUIRE CONVERT
t7
t8
Figure 33. Basic Conversion Timing
Although CNVST is a digital signal, it should be designed with special care with fast, clean edges, and levels with minimum overshoot, undershoot, or ringing. The CNVST trace should be shielded with ground and a low value (such as 50 ) serial resistor termination should be added close to the output of the component that drives this line. For applications where SNR is critical, the CNVST signal should have very low jitter. This can be achieved by using a dedicated oscillator for CNVST generation, or by clocking CNVST with a high frequency, low jitter clock, as shown in Figure 27.
POWER DISSIPATION (mW)
100
WARP MODE POWER
10
IMPULSE MODE POWER
1
10
100
1000
SAMPLING RATE (kSPS)
Figure 32. Power Dissipation vs. Sample Rate
06265-032
1
Rev. 0 | Page 23 of 32
06265-033
MODE
ACQUIRE
AD7612 INTERFACES
DIGITAL INTERFACE
The AD7612 has a versatile digital interface that can be set up as either a serial or a parallel interface with the host system. The serial interface is multiplexed on the parallel data bus. The AD7612 digital interface also accommodates 2.5 V, 3.3 V, or 5 V logic. In most applications, the OVDD supply pin is connected to the host system interface 2.5 V to 5.25 V digital supply. Finally, by using the OB/2C input pin, both twos complement or straight binary coding can be used. Two signals, CS and RD, control the interface. When at least one of these signals is high, the interface outputs are in high impedance. Usually, CS allows the selection of each AD7612 in multi-circuit applications and is held low in a single AD7612 design. RD is generally used to enable the conversion result on the data bus.
CS = RD = 0 CNVST
t1
t10
BUSY
t3
DATA BUS
t4 t11
PREVIOUS CONVERSION DATA NEW DATA
06265-035
Figure 35. Master Parallel Data Timing for Reading (Continuous Read)
Slave Parallel Interface
In slave parallel reading mode, the data can be read either after each conversion, which is during the next acquisition phase, or during the following conversion, as shown in Figure 36 and Figure 37, respectively. When the data is read during the conversion, it is recommended that it is read only during the first half of the conversion phase. This avoids any potential feedthrough between voltage transients on the digital interface and the most critical analog conversion circuitry.
CS
RESET
The RESET input is used to reset the AD7612. A rising edge on RESET aborts the current conversion (if any) and tristates the data bus. The falling edge of RESET resets the AD7612 and clears the data bus and configuration register. See Figure 34 for the RESET timing details.
t9
RESET
RD
BUSY
DATA BUS
BUSY
t8
06265-036
CNVST
06265-034
DATA BUS
CURRENT CONVERSION
Figure 34. RESET Timing
t12
t13
PARALLEL INTERFACE
The AD7612 is configured to use the parallel interface when SER/PAR is held low.
Figure 36. Slave Parallel Data Timing for Reading (Read After Convert)
CS = 0 CNVST, RD
t1
Master Parallel Interface
Data can be continuously read by tying CS and RD low, thus requiring minimal microprocessor connections. However, in this mode, the data bus is always driven and cannot be used in shared bus applications (unless the device is held in RESET). Figure 35 details the timing for this mode.
BUSY
t4 t3
t12
t13
Figure 37. Slave Parallel Data Timing for Reading (Read During Convert)
Rev. 0 | Page 24 of 32
06265-037
DATA BUS
PREVIOUS CONVERSION
AD7612
8-Bit Interface (Master or Slave)
The BYTESWAP pin allows a glueless interface to an 8-bit bus. As shown in Figure 38, when BYTESWAP is low, the LSB byte is output on D[7:0] and the MSB is output on D[15:8]. When BYTESWAP is high, the LSB and MSB bytes are swapped; the LSB is output on D[15:8] and the MSB is output on D[7:0]. By connecting BYTESWAP to an address line, the 16-bit data can be read in two bytes on either D[15:8] or D[7:0]. This interface can be used in both master and slave parallel reading modes.
MASTER SERIAL INTERFACE
The pins multiplexed on D[10:2] and used for master serial interface are DIVSCLK[0], DIVSCLK[1], EXT/INT, INVSYNC, INVSCLK, RDC, SDOUT, SDCLK and SYNC.
Internal Clock (SER/PAR = high, EXT/INT = Low)
The AD7612 is configured to generate and provide the serial data clock, SDCLK, when the EXT/INT pin is held low. The AD7612 also generates a SYNC signal to indicate to the host when the serial data is valid. The SDCLK, and the SYNC signals can be inverted, if desired using the INVSCLK and INVSYNC inputs, respectively. Depending on the input, RDC, the data can be read during the following conversion or after each conversion. Figure 39 and Figure 40 show detailed timing diagrams of these two modes.
CS
RD
BYTESWAP
Read During Convert (RDC = High)
PINS D[15:8] HI-Z HIGH BYTE LOW BYTE HI-Z
PINS D[7:0]
HI-Z
LOW BYTE
HIGH BYTE
HI-Z
Figure 38. 8-Bit and 16-Bit Parallel Interface
SERIAL INTERFACE
The AD7612 has a serial interface (SPI-compatible) multiplexed on the data pins D[15:2]. The AD7612 is configured to use the serial interface when SER/PAR is held high.
06265-038
t12
t12
t13
Setting RDC = high allows the master read (previous conversion result) during conversion mode. Usually, because the AD7612 is used with a fast throughput, this mode is the most recommended serial mode. In this mode, the serial clock and data toggle at appropriate instances, minimizing potential feed through between digital activity and critical conversion decisions. In this mode, the SDCLK period changes since the LSBs require more time to settle and the SDCLK is derived from the SAR conversion cycle. In this mode, the AD7612 generates a discontinuous SDCLK of two different periods and the host should use an SPI interface.
Data Interface
The AD7612 outputs 16 bits of data, MSB first, on the SDOUT pin. This data is synchronized with the 16 clock pulses provided on the SDCLK pin. The output data is valid on both the rising and falling edge of the data clock. Serial Configuration Interface The AD7612 can be configured through the serial configuration register only in serial mode as the serial configuration pins are also multiplexed on the data pins D[15:12]. Refer to the Hardware Configuration section and Software Configuration section for more information.
Read During Convert (RDC = Low, DIVSCLK[1:0] = [0 to 3])
Setting RDC = low allows the read after conversion mode. Unlike the other serial modes, the BUSY signal returns low after the 16 data bits are pulsed out and not at the end of the conversion phase, resulting in a longer BUSY width (refer to Table 4 for BUSY timing specifications). The DIVSCLK[1:0] inputs control the SDCLK period and SDOUT data rate. As a result, the maximum throughput cannot be achieved in this mode. In this mode, the AD7612 also generates a discontinuous SDCLK however, a fixed period and hosts supporting both SPI and serial ports can also be used.
Rev. 0 | Page 25 of 32
AD7612
EXT/INT = 0 CS, RD RDC/SDIN = 0 INVSCLK = INVSYNC = 0
t3
CNVST
BUSY
t28 t29 t30 t25 t18 t19
SYNC
t14 t20
SDCLK 1
t21
2 3 14 15
t24
16
t26 t27
t15
SDOUT X D15 D14 D2 D1 D0
t16
t22
t23
Figure 39. Master Serial Data Timing for Reading (Read After Convert)
EXT/INT = 0 CS, RD
RDC/SDIN = 1
INVSCLK = INVSYNC = 0
t1
CNVST
t3
BUSY
t17
SYNC
t25 t19 t20 t21
2 3 14 15 16
t14
t24
SDCLK
t15 t18
t26 t27
1
SDOUT
X
D15
D14
D2
D1
D0
06265-040
t16
t22
t23
Figure 40. Master Serial Data Timing for Reading (Read Previous Conversion During Convert)
Rev. 0 | Page 26 of 32
06265-039
AD7612
SLAVE SERIAL INTERFACE
The pins multiplexed on D[11:4] used for slave serial interface are: EXT/INT, INVSCLK, SDIN, SDOUT, SDCLK and RDERROR. edge of SDCLK used to shift out the data on SDOUT (SDCLK falling edge when INVSCLK = low). Therefore, the MSB of the upstream converter follows the LSB of the downstream converter on the next SDCLK cycle. In this mode, the 40 MHz SDCLK rate cannot be used since the SDIN to SDCLK setup time, t33, is less than the minimum time specified. (SDCLK to SDOUT delay, t32, is the same for all converters when simultaneously sampled). For proper operation, the SDCLK edge for latching SDIN (or 1/2 period of SDCLK) needs to be:
t 1 / 2 SDCLK = t 32 + t 33
External Clock (SER/PAR = High, EXT/INT = High)
Setting the EXT/INT = high allows the AD7612 to accept an externally supplied serial data clock on the SDCLK pin. In this mode, several methods can be used to read the data. The external serial clock is gated by CS. When CS and RD are both low, the data can be read after each conversion or during the following conversion. A clock can be either normally high or normally low when inactive. For detailed timing diagrams, see Figure 42 and Figure 43. While the AD7612 is performing a bit decision, it is important that voltage transients be avoided on digital input/output pins, or degradation of the conversion result may occur. This is particularly important during the last 475 ns of the conversion phase because the AD7612 provides error correction circuitry that can correct for an improper bit decision made during the first part of the conversion phase. For this reason, it is recommended that any external clock provided, is a discontinuous clock that transitions only when BUSY is low, or, more importantly, that it does not transition during the last 475 ns of BUSY high.
Or the max SDCLK frequency needs to be: 1 f SDCLK = 2(t 32 + t 33 )
If not using the daisy-chain feature, the SDIN input should be tied either high or low.
BUSY OUT BUSY BUSY
AD7612
#2 (UPSTREAM) RDC/SDIN SDOUT CNVST CS SCLK SCLK IN CS IN CNVST IN
AD7612
#1 (DOWNSTREAM) RDC/SDIN SDOUT CNVST CS SCLK DATA OUT
External Discontinuous Clock Data Read After Conversion
Though the maximum throughput cannot be achieved using this mode, it is the most recommended of the serial slave modes. Figure 42 shows the detailed timing diagrams for this method. After a conversion is complete, indicated by BUSY returning low, the conversion result can be read while both CS and RD are low. Data is shifted out MSB first with 16 clock pulses and, depending on the SDCLK frequency, can be valid on the falling and rising edges of the clock. One advantage of this method is that conversion performance is not degraded because there are no voltage transients on the digital interface during the conversion process. Another advantage is the ability to read the data at any speed up to 40 MHz, which accommodates both the slow digital host interface and the fastest serial reading.
Figure 41. Two AD7612 Devices in a Daisy-Chain Configuration
External Clock Data Read During Previous Conversion
Figure 43 shows the detailed timing diagrams for this method. During a conversion, while both CS and RD are low, the result of the previous conversion can be read. Data is shifted out MSB first with 16 clock pulses and, depending on the SDCLK frequency, can be valid on the falling and rising edges of the clock. The 16 bits have to be read before the current conversion is complete; otherwise, RDERROR is pulsed high and can be used to interrupt the host interface to prevent incomplete data reading. To reduce performance degradation due to digital activity, a fast discontinuous clock of at least 40 MHz is recommended to ensure that all the bits are read during the first half of the SAR conversion phase. The daisy-chain feature should not be used in this mode since digital activity occurs during the second half of the SAR conversion phase likely resulting in performance degradation.
Daisy-Chain Feature
Also in the read after convert mode, the AD7612 provides a daisychain feature for cascading multiple converters together using the serial data input, SDIN, pin. This feature is useful for reduceing component count and wiring connections when desired, for instance, in isolated multiconverter applications. See Figure 42 for the timing details. An example of the concatenation of two devices is shown in Figure 41. Simultaneous sampling is possible by using a common CNVST signal. Note that the SDIN input is latched on the opposite
Rev. 0 | Page 27 of 32
06265-041
AD7612
External Clock Data Read After/During Conversion
It is also possible to begin to read data after conversion and continue to read the last bits after a new conversion has been initiated. This method allows the full throughput and the use of a slower SDCLK frequency. Again, it is recommended to use a discontinuous SDCLK whenever possible to minimize potential incorrect bit decisions. For the different modes, the use of a slower SDCLK such as 20 MHz in warp mode, 15 MHz in normal mode and 13 MHz in impulse mode can be used.
SER/PAR = 1
EXT/INT = 1
INVSCLK = 0
RD = 0
CS
BUSY
t31
SDCLK X* 1
t31
2 3
t35
t36
4 14 15 16 17 18 19
t32
SDOUT D15 D14
t37
D13 D2 D1 D0 X15 X14
t16
SDIN X15 X14 X13 X2 X1 X0 Y15 Y14
06265-042
t33
*A DISCONTINUOUS SDCLK IS RECOMMENDED.
t34
Figure 42. Slave Serial Data Timing for Reading (Read After Convert)
SER/PAR = 1 CS
EXT/INT = 1
INVSCLK = 0
RD = 0
CNVST
BUSY
t31
SDCLK X* 1
t31
2 3 15
t35
t36
16 X* X* X* X* X*
t32
SDOUT D15 D14
t37
D1 D0 DATA = SDIN
*A DISCONTINUOUS SDCLK IS RECOMMENDED.
Figure 43. Slave Serial Data Timing for Reading (Read Previous Conversion During Convert)
Rev. 0 | Page 28 of 32
06265-043
t16
t27
AD7612
HARDWARE CONFIGURATION
The AD7612 can be configured at any time with the dedicated hardware pins WARP, IMPULSE, BIPOLAR, TEN, OB/2C, and PD for parallel mode (SER/PAR = low) or serial hardware mode (SER/ PAR = high, HW/SW = high). Programming the AD7612 for mode selection and input range configuration can be done before or during conversion. Like the RESET input, the ADC requires at least one acquisition time to settle as indicated in Figure 44. See Table 6 for pin descriptions. Note that these inputs are high impedance when using the software configuration mode. recommended to write to the SCP during the last 475 ns of conversion (BUSY = high) or performance degradation can result. In addition, the SCP can be accessed in both serial master and serial slave read during and read after convert modes. Note that at power up, the configuration register is undefined. The RESET input clears the configuration register (sets all bits to 0), thus placing the configuration to 0 V to 5 V input, normal mode, and twos complemented output.
Table 9. Configuration Register Description
Bit 8 Name START Description START bit. With the SCP enabled (SCCS = low), when START is high, the first rising edge of SCCLK (INVSCLK = low) begins to load the register with the new configuration. Input Range Select. Used in conjunction with Bit 6, TEN, per the following: Input Range BIPOLAR TEN 0 V to 5 V Low Low 0 V to 10 V Low High 5 V High Low 10 V Low High Input Range Select. See Bit 7, BIPOLAR. Power Down. PD = Low, normal operation. PD = High, power down the ADC. The SCP is accessible while in power down. To power up the ADC, write PD = low on the next configuration setting. Mode Select. Used in conjunction with Bit 3, WARP per the following: Mode WARP IMPULSE Normal Low Low Impulse Low High Warp High Low Normal High High Mode Select. See Bit 4, IMPULSE. Output Coding OB/2C = Low, use twos complement output. OB/2C = High, use straight binary output. Reserved. Reserved.
SOFTWARE CONFIGURATION
The pins multiplexed on D[15:12] used for software configuration are: HW/SW, SCIN, SCCLK, and SCCS. The AD7612 is programmed using the dedicated write-only serial configurable port (SCP) for conversion mode, input range selection, output coding, and power-down using the serial configuration register. See Table 9 for details of each bit in the configuration register. The SCP can only be used in serial software mode selected with SER/PAR = high and HW/SW = low since the port is multiplexed on the parallel interface. The SCP is accessed by asserting the port's chip select, SCCS, and then writing SCIN synchronized with SCCLK, which (like SDCLK) is edge sensitive depending on the state of INVSCLK. See Figure 45 for timing details. SCIN is clocked into the configuration register MSB first. The configuration register is an internal shift register that begins with Bit 8, the start bit. The 9th SPPCLK edge updates the register and allows the new settings to be used. As indicated in the timing diagram, at least one acquisition time is required from the 9th SCCLK edge. Bits [1:0] are reserved bits and are not written to while the SCP is being updated. The SCP can be written to at any time, up to 40 MHz, and it is recommended to write to while the AD7612 is not busy converting, as detailed in Figure 45. In this mode, the full 750 kSPS is not attainable because the time required for SCP access is (t31 + 8 x 1/ SCCLK +t8) minimum. If the full throughput is required, the SCP can be written to during conversion, however it is not
HW/SW = 0
7
BIPOLAR
6 5
TEN PD
4
IMPULSE
3 2
WARP OB/2C
1 0
RSV RSV
PD = 0
SER/PAR = 0, 1
t8
t8
CNVST
BUSY
BIPOLAR, TEN
Figure 44. Hardware Configuration Timing
Rev. 0 | Page 29 of 32
06265-044
WARP, IMPULSE
AD7612
WARP = 0 OR 1 IMPULSE = 0 OR 1 BIP = 0 OR 1 TEN = 0 OR 1 SER/PAR = 1 HW/SW = 0 INVSCLK = 0 PD = 0
t8
CNVST
BUSY
t31
SCCS
t31
SCCLK 1 2 3 4
t35
t36
5 6 7 8 9
t37 t34
SCIN X START
BIPOLAR
TEN
PD
IMPULSE
WARP
OB/2C
X
06265-045
t33
Figure 45. Serial Configuration Port Timing
MICROPROCESSOR INTERFACING
The AD7612 is ideally suited for traditional dc measurement applications supporting a microprocessor, and ac signal processing applications interfacing to a digital signal processor. The AD7612 is designed to interface with a parallel 8-bit or 16-bit wide interface, or with a general-purpose serial port or I/O ports on a microcontroller. A variety of external buffers can be used with the AD7612 to prevent digital noise from coupling into the ADC.
the DSP. The serial peripheral interface (SPI) on the ADSP-219x is configured for master mode (MSTR) = 1, clock polarity bit (CPOL) = 0, clock phase bit (CPHA) = 1, and SPI interrupt enable (TIMOD) = 0 by writing to the SPI control register (SPICLTx). It should be noted that to meet all timing requirements, the SPI clock should be limited to 17 Mbps allowing it to read an ADC result in less than 1 s. When a higher sampling rate is desired, use one of the parallel interface modes.
DVDD
SPI Interface
The AD7612 is compatible with SPI and QSPI digital hosts and DSPs such as Blackfin(R) ADSP-BF53x and ADSP-218x/ADSP-219x. Figure 46 shows an interface diagram between the AD7612 and the SPI-equipped ADSP-219x. To accommodate the slower speed of the DSP, the AD7612 acts as a slave device, and data must be read after conversion. This mode also allows the daisy-chain feature. The convert command could be initiated in response to an internal timer interrupt. The reading process can be initiated in response to the end-ofconversion signal (BUSY going low) using an interrupt line of
AD76121
SER/PAR BUSY EXT/INT CS SDOUT RD SCLK INVSCLK CNVST
ADSP-219x1
PFx SPIxSEL (PFx) MISOx SCKx PFx OR TFSx
06265-046
1ADDITIONAL
PINS OMITTED FOR CLARITY.
Figure 46. Interfacing the AD7612 to SPI Interface
Rev. 0 | Page 30 of 32
AD7612 APPLICATION INFORMATION
LAYOUT GUIDELINES
While the AD7612 has very good immunity to noise on the power supplies, exercise care with the grounding layout. To facilitate the use of ground planes that can be easily separated, design the printed circuit board that houses the AD7612 so that the analog and digital sections are separated and confined to certain areas of the board. Digital and analog ground planes should be joined in only one place, preferably underneath the AD7612, or as close as possible to the AD7612. If the AD7612 is in a system where multiple devices require analog-to-digital ground connections, the connections should still be made at one point only, a star ground point, established as close as possible to the AD7612. To prevent coupling noise onto the die, avoid radiating noise, and to reduce feedthrough: * Do not run digital lines under the device. * Do run the analog ground plane under the AD7612. * Do shield fast switching signals, like CNVST or clocks, with digital ground to avoid radiating noise to other sections of the board, and never run them near analog signal paths. * Avoid crossover of digital and analog signals. * Run traces on different but close layers of the board, at right angles to each other, to reduce the effect of feedthrough through the board. The power supply lines to the AD7612 should use as large a trace as possible to provide low impedance paths and reduce the effect of glitches on the power supply lines. Good decoupling is also important to lower the impedance of the supplies presented to the AD7612, and to reduce the magnitude of the supply spikes. Decoupled ceramic capacitors, typically 100 nF, should be placed on each of the power supplies pins, AVDD, DVDD, and OVDD, VCC, and VEE. The capacitors should be placed close to, and ideally right up against, these pins and their corresponding ground pins. Additionally, low ESR 10 F capacitors should be located in the vicinity of the ADC to further reduce low frequency ripple. * The DVDD supply of the AD7612 can be either a separate supply or come from the analog supply, AVDD, or from the digital interface supply, OVDD. When the system digital supply is noisy, or fast switching digital signals are present, and no separate supply is available, it is recommended to connect the DVDD digital supply to the analog supply AVDD through an RC filter, and to connect the system supply to the interface digital supply OVDD and the remaining digital circuitry. See Figure 27 for an example of this configuration. When DVDD is powered from the system supply, it is useful to insert a bead to further reduce high frequency spikes. The AD7612 has four different ground pins: REFGND, AGND, DGND, and OGND. * REFGND senses the reference voltage and, because it carries pulsed currents, should be a low impedance return to the reference. AGND is the ground to which most internal ADC analog signals are referenced; it must be connected with the least resistance to the analog ground plane. DGND must be tied to the analog or digital ground plane depending on the configuration. OGND is connected to the digital system ground.
* *
The layout of the decoupling of the reference voltage is important. To minimize parasitic inductances, place the decoupling capacitor close to the ADC and connect it with short, thick traces.
EVALUATING PERFORMANCE
A recommended layout for the AD7612 is outlined in the EVALAD7612CB evaluation board documentation. The evaluation board package includes a fully assembled and tested evaluation board, documentation, and software for controlling the board from a PC via the EVAL-CONTROL BRD3.
Rev. 0 | Page 31 of 32
AD7612 OUTLINE DIMENSIONS
0.75 0.60 0.45 1.60 MAX
48 1
PIN 1
9.20 9.00 SQ 8.80
37 36
1.45 1.40 1.35
TOP VIEW
0.20 0.09 7 3.5 0 0.08 COPLANARITY
(PINS DOWN)
7.20 7.00 SQ 6.80
0.15 0.05
12 13 24
25
SEATING PLANE
VIEW A
0.50 BSC LEAD PITCH
ROTATED 90 CCW
COMPLIANT TO JEDEC STANDARDS MS-026-BBC
Figure 47. 48-Lead Low Profile Quad Flat Package [LQFP] (ST-48) Dimensions shown in millimeters
7.00 BSC SQ 0.60 MAX 0.60 MAX
37 36
0.30 0.23 0.18
48 1
PIN 1 INDICATOR
PIN 1 INDICATOR
TOP VIEW
6.75 BSC SQ
EXPOSED PAD
(BOTTOM VIEW)
5.25 5.10 SQ 4.95
0.50 0.40 0.30
25 24
13
12
0.25 MIN 5.50 REF PADDLE CONNECTED TO VEE. THIS CONNECTION IS NOT REQUIRED TO MEET THE ELECTRICAL PERFORMANCES.
1.00 0.85 0.80
12 MAX
0.80 MAX 0.65 TYP 0.05 MAX 0.02 NOM 0.50 BSC
SEATING PLANE
0.20 REF
COPLANARITY 0.08
COMPLIANT TO JEDEC STANDARDS MO-220-VKKD-2
Figure 48. 48-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 7 mm x 7 mm Body, Very Thin Quad (CP-48-1) Dimensions shown in millimeters
ORDERING GUIDE
Model AD7612BCPZ1 AD7612BCPZ-RL1 AD7612BSTZ1 AD7612BSTZ-RL1 EVAL-AD7612CB2 EVAL-CONTROL BRD33
1 2
Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Package Description 48-Lead Lead Frame Chip Scale Package (LFCSP_VQ) 48-Lead Lead Frame Chip Scale Package (LFCSP_VQ) 48-Lead Low Profile Quad Flat Package (LQFP) 48-Lead Low Profile Quad Flat Package (LQFP) Evaluation Board Controller Board
051706-A
VIEW A
0.27 0.22 0.17
Package Option CP-48-1 CP-48-1 ST-48 ST-48
Z = Pb-free part. This board can be used as a standalone evaluation board or in conjunction with the EVAL-CONTROL BRD3 for evaluation/demonstration purposes. 3 This board allows a PC to control and communicate with all Analog Devices. evaluation boards ending with the CB designators.
(c)2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06265-0-10/06(0)
Rev. 0 | Page 32 of 32

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