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19-1686; Rev 0; 5/00
400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference
General Description
The MAX1084/MAX1085 10-bit analog-to-digital converters (ADCs) combine a high-bandwidth track/hold, a serial interface with high conversion speed, an internal +2.5V reference, and low power consumption. The MAX1084 operates from a single +4.5V to +5.5V supply; the MAX1085 operates from a single +2.7V to +3.6V supply. The 3-wire serial interface connects directly to SPITM/QSPITM/MICROWIRETM devices without external logic. The devices use an external serial-interface clock to perform successive-approximation analog-to-digital conversions. Low power combined with ease of use and small package size make these converters ideal for remote-sensor and data-acquisition applications, or for other circuits with demanding power consumption and space requirements. The MAX1084/MAX1085 are available in 8-pin SO packages. These devices are pin-compatible, higher-speed versions of the MAX1242/MAX1243; for more information, refer to the respective data sheets. o Single-Supply Operation +4.5V to +5.5V (MAX1084) +2.7V to +3.6V (MAX1085) o 10-Bit Resolution o 400ksps Sampling Rate (MAX1084) o Internal Track/Hold o Internal +2.5V Reference o Low Power: 2.5mA (400ksps) o SPI/QSPI/MICROWIRE 3-Wire Serial Interface o Pin-Compatible, High-Speed Upgrade to MAX1242/MAX1243 o 8-Pin SO Package
Features
MAX1084/MAX1085
Ordering Information
PART MAX1084ACSA MAX1084BCSA MAX1084AESA MAX1084BESA MAX1085ACSA MAX1085BCSA MAX1085AESA MAX1085BESA TEMP. RANGE 0C to +70C 0C to +70C -40C to +85C -40C to +85C 0C to +70C 0C to +70C -40C to +85C -40C to +85C PINPACKAGE 8 SO 8 SO 8 SO 8 SO 8 SO 8 SO 8 SO 8 SO INL (LSB) 1/2 1 1/2 1 1/2 1 1/2 1
Applications
Portable Data Logging Data Acquisition Medical Instruments Battery-Powered Instruments Pen Digitizers Process Control
Pin Configuration
TOP VIEW
CS SCLK 7 8 3 CONTROL LOGIC
Functional Diagram
VDD 1
VDD AIN
1 2
8 7
SCLK CS DOUT GND
SHDN
INT CLOCK
SHDN 3 REF 4
MAX1084 MAX1085
6 5
OUTPUT SHIFT REGISTER
6
DOUT
AIN
2
T/H 2.5V REFERENCE
10-BIT SAR
SO
REF 4
MAX1084 MAX1085
5 GND
SPI and QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor Corp.
________________________________________________________________ Maxim Integrated Products
1
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400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference MAX1084/MAX1085
ABSOLUTE MAXIMUM RATINGS
VDD to GND .............................................................-0.3V to +6V AIN to GND................................................-0.3V to (VDD + 0.3V) REF to GND ...............................................-0.3V to (VDD + 0.3V) Digital Inputs to GND...............................................-0.3V to +6V DOUT to GND............................................-0.3V to (VDD + 0.3V) DOUT Current ..................................................................25mA Continuous Power Dissipation (TA = +70C) 8-Pin SO (derate 5.88mW/C above +70C) ..............471mW Operating Temperature Ranges MAX1084_CSA/MAX1085_CSA.........................0C to +70C MAX1084_ESA/MAX1085_ESA ......................-40C to +85C Storage Temperature Range............................-60C to +150C Lead Temperature (soldering, 10s) ................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS--MAX1084
(VDD = +4.5V to +5.5V, fSCLK = 6.4MHz, 50% duty cycle, 16 clocks/conversion cycle (400ksps), 4.7F capacitor at REF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER DC ACCURACY (Note 1) Resolution Relative Accuracy (Note 2) Differential Nonlinearity Offset Error Gain Error (Note 3) Gain-Error Temperature Coefficient DYNAMIC SPECIFICATIONS (100kHz sine wave, 2.5Vp-p, clock = 6.4MHz) Signal-to-Noise Plus Distortion Ratio Total Harmonic Distortion Spurious-Free Dynamic Range Intermodulation Distortion Full-Power Bandwidth Full-Linear Bandwidth CONVERSION RATE Conversion Time (Note 4) Track/Hold Acquisition Time Aperture Delay Aperture Jitter Serial Clock Frequency Duty Cycle ANALOG INPUT (AIN) Input Voltage Range Input Capacitance VAIN 0 18 2.5 V pF fSCLK 0.5 40 tCONV tACQ 10 <50 6.4 60 2.5 468 s ns ns ps MHz % SINAD THD SFDR IMD fIN1 = 99kHz, fIN2 =102kHz -3dB point SINAD > 58dB Up to the 5th harmonic 60 -70 70 76 6 350 dB dB dB dB MHz kHz 0.8 INL DNL MAX1084A MAX1084B No missing codes over temperature 10 0.5 1.0 1.0 4.0 3.0 Bits LSB LSB LSB LSB ppm/C SYMBOL CONDITIONS MIN TYP MAX UNITS
2
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400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference
ELECTRICAL CHARACTERISTICS--MAX1084 (continued)
(VDD = +4.5V to +5.5V, fSCLK = 6.4MHz, 50% duty cycle, 16 clocks/conversion cycle (400ksps), 4.7F capacitor at REF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER INTERNAL REFERENCE REF Output Voltage REF Short-Circuit Current REF Output Tempco Load Regulation (Note 5) Capacitive Bypass at REF DIGITAL INPUTS (SCLK, CS, SHDN) Input High Voltage Input Low Voltage Input Hysteresis Input Leakage Input Capacitance DIGITAL OUTPUT (DOUT) Output Voltage Low Output Voltage High Three-State Leakage Current Three-State Output Capacitance POWER SUPPLY Positive Supply Voltage (Note 6) Positive Supply Current (Note 7) Shutdown Supply Current Power-Supply Rejection VDD IDD ISHDN PSR VDD = 5.5V SCLK = VDD, SHDN = GND VDD = 5V 10%, midscale input 4.5 2.5 2 0.5 5.5 4.0 10 2.0 V mA A mV VOL VOH IL COUT ISINK = 5mA ISOURCE = 1mA CS = 5V CS = 5V 15 4 10 0.4 V V A pF VINH VINL VHYST IIN CIN VIN = 0 or VDD 15 0.2 1 3.0 0.8 V V V A pF TC VREF 0 to 1.0mA output load 4.7 VREF TA = +25C 2.48 2.50 30 15 0.1 2.0 10 2.52 V mA ppm/C mV/mA F SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX1084/MAX1085
ELECTRICAL CHARACTERISTICS--MAX1085
(VDD = +2.7V to +3.6V, fSCLK = 4.8MHz, 50% duty cycle, 16 clocks/conversion cycle (300ksps), 4.7F capacitor at REF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER DC ACCURACY (Note 1) Resolution Relative Accuracy (Note 2) Differential Nonlinearity Offset Error Gain Error (Note 3) Gain-Error Temperature Coefficient 1.6 INL DNL MAX1085A MAX1085B No missing codes over temperature 10 0.5 1.0 1.0 3.0 3.0 Bits LSB LSB LSB LSB ppm/C 3 SYMBOL CONDITIONS MIN TYP MAX UNITS
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400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference MAX1084/MAX1085
ELECTRICAL CHARACTERISTICS--MAX1085 (continued)
(VDD = +2.7V to +3.6V, fSCLK = 4.8MHz, 50% duty cycle, 16 clocks/conversion cycle (300ksps), 4.7F capacitor at REF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Signal-to-Noise Plus Distortion Ratio Total Harmonic Distortion Spurious-Free Dynamic Range Intermodulation Distortion Full-Power Bandwidth Full-Linear Bandwidth CONVERSION RATE Conversion Time (Note 4) Track/Hold Acquisition Time Aperture Delay Aperture Jitter Serial Clock Frequency Duty Cycle ANALOG INPUT Input Voltage Range Input Capacitance INTERNAL REFERENCE REF Output Voltage REF Short Circuit Current REF Output Tempco Load Regulation (Note 5) Capacitive Bypass at REF DIGITAL INPUTS (SCLK,CS, SHDN) Input High Voltage Input Low Voltage Input Hysteresis Input Leakage Input Capacitance DIGITAL OUTPUTS (DOUT) Output Voltage Low Output Voltage High Three-State Leakage Current Three-State Output Capacitance POWER SUPPLY Positive Supply Voltage (Note 6) Positive Supply Current (Note 7) Shutdown Supply Current Power-Supply Rejection 4 VOL VOH IL COUT VDD IDD ISHDN PSR VDD = 3.6V SCLK = VDD, SHDN = GND VDD = 2.7V to 3.6V, midscale input ISINK = 5mA ISOURCE = 0.5mA CS = 3V CS = 3V 2.7 2.5 2 0.5 15 3.6 3.5 10 2.0 VDD - 0.5V 10 0.4 V V A pF V mA A mV VINH VINL VHYST IIN CIN VIN = 0 or VDD 15 0.2 1 2.0 0.8 V V V A pF TC VREF 0 to 0.75mA output load 4.7 VREF TA = +25C 2.48 2.50 15 15 0.1 2.0 10 2.52 V mA ppm/C mV/mA F VAIN CIN 0 18 2.5 V pF fSCLK 0.5 40 tCONV tACQ 10 <50 4.8 60 3.3 625 s ns ns ps MHz % SYMBOL CONDITIONS MIN TYP MAX UNITS DYNAMIC SPECIFICATIONS (75kHz sinewave, 2.5Vp-p, fSAMPLE = 300ksps, fSCLK = 4.8MHz) SINAD THD SFDR IMD fIN1 = 99kHz, fIN2 =102kHz -3dB point SINAD > 58dB Up to the 5th harmonic 60 -70 70 76 3 250 dB dB dB dB MHz kHz
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400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference MAX1084/MAX1085
TIMING CHARACTERISTICS--MAX1084
(Figures 1, 2, 8, 9; VDD = +4.5V to +5.5V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SCLK Period SCLK Pulse Width High SCLK Pulse Width Low CS Fall to SCLK Rise Setup SCLK Rise to CS Rise Hold SCLK Rise to CS Fall Ignore CS Rise to SCLK Rise Ignore SCLK Rise to DOUT Hold SCLK Rise to DOUT Valid CS Rise to DOUT Disable CS Fall to DOUT Enable CS Pulse Width High SYMBOL tCP tCH tCL tCSS tCSH tCSO tCS1 tDOH tDOV tDOD tDOE tCSW CLOAD = 20pF CLOAD = 20pF CLOAD = 20pF CLOAD = 20pF 100 10 CONDITIONS MIN 156 62 62 35 0 35 35 10 80 65 65 TYP MAX UNITS ns ns ns ns ns ns ns ns ns ns ns ns
TIMING CHARACTERISTICS--MAX1085
(Figures 1, 2, 8, 9; VDD = +2.7V to +3.6V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SCLK Period SCLK Pulse Width High SCLK Pulse Width Low CS Fall to SCLK Rise Setup SCLK Rise to CS Rise Hold SCLK Rise to CS Fall Ignore CS Rise to SCLK Rise Ignore SCLK Rise to DOUT Hold SCLK Rise to DOUT Valid CS Rise to DOUT Disable CS Fall to DOUT Enable CS Pulse Width High SYMBOL tCP tCH tCL tCSS tCSH tCSO tCS1 tDOH tDOV tDOD tDOE tCSW CLOAD = 20pF CLOAD = 20pF CLOAD = 20pF CLOAD = 20pF CLOAD = 20pF 100 13 CONDITIONS MIN 208 83 83 45 0 45 45 13 100 85 85 TYP MAX UNITS ns ns ns ns ns ns ns ns ns ns ns ns
Note 1: Tested at VDD = VDD,MIN. Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after the full-scale range has been calibrated. Note 3: Internal reference, offset, and reference errors nulled. Note 4: Conversion time is defined as the number of clock cycles multiplied by the clock period; clock has 50% duty cycle. Note 5: External load should not change during conversion for specified accuracy. Guaranteed specification limit of 2mV/mA due to production test limitation. Note 6: Electrical characteristics are guaranteed from VDD,MIN to VDD,MAX. For operations beyond this range, see Typical Operating Characteristics. Note 7: MAX1084 tested with 20pF on DOUT and fSCLK = 6.4MHz, 0 to 5V. MAX1085 tested with same loads, fSCLK = 4.8MHz, 0 to 3V. DOUT = full scale.
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400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference MAX1084/MAX1085
Typical Operating Characteristics
(MAX1084: VDD = +5.0V, fSCLK = 6.4MHz; MAX1055: VDD = +3.0V, fSCLK = 4.8MHz; CLOAD = 20pF, 4.7F capacitor at REF, TA = +25C, unless otherwise noted.)
INTEGRAL NONLINEARLITY vs. DIGITAL OUTPUT CODE
MAX1084/5toc01
DIFFERENTIAL NONLINEARITY vs. DIGITAL OUTPUT CODE
MAX1084/5toc02
OFFSET ERROR vs. SUPPLY VOLTAGE
MAX1084/5 toc03
0.10 0.08 0.06 0.04
0.15 0.10 0.05 DNL (LSB) 0
0.50
OFFSET ERROR (LSB)
0.25
INL (LSB)
0.02 0 -0.02 -0.04 -0.06 -0.08 -0.10 0 200 400 600 800 1000 1200 DIGITAL OUTPUT CODE
-0.05 -0.10 -0.15 0 200 400 600 800 1000 1200 DIGITAL OUTPUT CODE
0
-0.25 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 VDD (V)
OFFSET ERROR vs. TEMPERATURE
MAX104/5 toc04
GAIN ERROR vs. SUPPLY VOLTAGE
0.20 0.15 GAIN ERROR (LSB) 0.10 0.05 0 -0.05 -0.10 -0.15 -0.20 -0.25 -0.50
MAX1084/5 toc05
GAIN ERROR vs. TEMPERATURE
MAX1084/5 toc06
0.45 0.40 0.35 OFFSET ERROR (LSB) 0.30 0.25 0.20 0.15 0.10 0.05 0 -40 -20 0 20 40 60 80
0.25
0.25
GAIN ERROR (LSB)
0
-0.25
100
2.5
3.0
3.5
4.0 VDD (V)
4.5
5.0
5.5
-40
-20
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
6
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400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference
Typical Operating Characteristics (continued)
(MAX1084: VDD = +5.0V, fSCLK = 6.4MHz; MAX1085: VDD = +3.0V, fSCLK = 4.8MHz; CLOAD = 20pF, 4.7F capacitor at REF, TA = +25C, unless otherwise noted.)
INTERNAL REFERENCE VOLTAGE vs. SUPPLY VOLTAGE
MAX1084/5 toc07
MAX1084/MAX1085
INTERNAL REFERENCE VOLTAGE vs. TEMPERATURE
2.508 2.506 2.504 VREF (V) 2.502 2.500 2.498 2.496 2.494 2.492 2.490
MAX1084/5 toc08
2.510 2.508 2.506 2.504 VREF (V) 2.502 2.500 2.498 2.496 2.494 2.492 2.490 2.5 3.0 3.5 4.0 4.5 5.0
2.510
5.5
-40
-20
0
20
40
60
80
100
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
CODE = 1111 1111 1111 RL = CL = 10pF CONVERTING, SCLK = 6.4MHz
MAX1084/5 toc09
SUPPLY CURRENT vs. TEMPERATURE
VDD = 5V, CONVERTING 2.7 SUPPLY CURRENT (mA)
MAX1084/5 toc10
3.00 2.75 SUPPLY CURRENT (mA) 2.50 2.25 2.00 1.75 1.50
3.0
2.4
VDD = 3V, CONVERTING
CONVERTING, SCLK = 4.8MHz
2.1
STATIC
1.8
VDD = 5V, STATIC
VDD = 3V, STATIC
1.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -40 -20 0 20 40 60 80 100 SUPPLY VOLTAGE (V) TEMPERATURE (C)
Pin Description
PIN 1 2 3 4 5 6 7 8 NAME VDD AIN SHDN REF GND DOUT CS SCLK Positive Supply Voltage Sampling Analog Input, 0 to VREF Range Active-Low Shutdown Input. Pulling SHDN low shuts down the device and reduces the supply current to 2A (typ). Reference Voltage for Analog-to-Digital Conversion. Internal 2.5V reference output. Bypass with a 4.7F capacitor. Analog and Digital Ground Serial Data Output. DOUT changes state at SCLK's rising edge. High impedance when CS is high. Active-Low Chip Select. Initiates conversions on the falling edge. When CS is high, DOUT is high impedance. Serial Clock Input. SCLK drives the conversion process and clocks data out at rates up to 6.4MHz (MAX1084) or 4.8MHz (MAX1085). 7 FUNCTION
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400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference MAX1084/MAX1085
VDD
6k DOUT 6k DGND a) HIGH-Z TO VOH AND VOL TO VOH b) HIGH-Z TO VOL AND VOH TO VOL CLOAD = 20pF DOUT CLOAD = 20pF DGND
Figure 1. Load Circuits for DOUT Enable Time
VDD
6k DOUT 6k DGND a) VOH TO HIGH-Z b) VOLTO HIGH-Z CLOAD = 20pF DOUT CLOAD = 20pF DGND
Figure 2. Load Circuits for DOUT Disable Time
_______________Detailed Description
Converter Operation
The MAX1084/MAX1085 use an input track/hold (T/H) and successive-approximation register (SAR) circuitry to convert an analog input signal to a digital 10-bit output. Figure 3 shows the MAX1084/MAX1085 in their simplest configuration. The internal reference is trimmed to 2.5V. The serial interface requires only three digital lines (SCLK, CS, and DOUT) and provides an easy interface to microprocessors (Ps). The MAX1084/MAX1085 have two modes: normal and shutdown. Pulling SHDN low shuts the device down and reduces supply current to 2A (typ); pulling SHDN high puts the device into operational mode. Pulling CS low initiates a conversion that is driven by SCLK. The conversion result is available at DOUT in unipolar serial format. The serial data stream consists of three zeros, followed by the data bits (MSB first). All transitions on DOUT occur 20ns after the rising edge of SCLK. Figures 8 and 9 show the interface timing information.
8
Analog Input
Figure 4 shows the sampling architecture of the ADC's comparator. The full-scale input voltage is set by the internal reference (VREF = +2.5V). Track/Hold In track mode, the analog signal is acquired and stored in the internal hold capacitor. In hold mode, the T/H switch opens and maintains a constant input to the ADC's SAR section. During acquisition, the analog input AIN charges capacitor CHOLD. Bringing CS low ends the acquisition interval. At this instant, the T/H switches the input side of CHOLD to GND. The retained charge on CHOLD represents a sample of the input, unbalancing node ZERO at the comparator's input. In hold mode, the capacitive digital-to-analog converter (DAC) adjusts during the remainder of the conversion cycle to restore node ZERO to 0 within the limits of 10bit resolution. This action is equivalent to transferring a charge from CHOLD to the binary-weighted capacitive
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400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference
DAC, which in turn forms a digital representation of the analog input signal. At the conversion's end, the input side of C HOLD switches back to AIN, and C HOLD charges to the input signal again. The time required for the T/H to acquire an input signal is a function of how quickly its input capacitance is charged. If the input signal's source impedance is high, the acquisition time lengthens, and more time must be allowed between conversions. The acquisition time, tACQ, is the maximum time the device takes to acquire the signal and the minimum time needed for the signal to be acquired. Acquisition time is calculated by: tACQ = 7(RS + RIN) 12pF where R IN = 800, R S = the input signal's source impedance, and t ACQ is never less than 468ns (MAX1284) or 625ns (MAX1085). Source impedance below 4k does not significantly affect the ADC's AC performance. Higher source impedances can be used if a 0.01F capacitor is connected to the analog input. Note that the input capacitor forms an RC filter with the input source impedance, limiting the ADC's input signal bandwidth. Input Bandwidth The ADC's input tracking circuitry has a 6MHz (MAX1084) or 3MHz (MAX1085) small-signal bandwidth, so it is possible to digitize high-speed transient events and measure periodic signals with bandwidths exceeding the ADC's sampling rate by using undersampling techniques. To avoid aliasing of unwanted high-frequency signals into the frequency band of interest, anti-alias filtering is recommended. Analog Input Protection Internal protection diodes, which clamp the analog input to VDD and GND, allow the input to swing from GND - 0.3V to VDD + 0.3V without damage. If the analog input exceeds 50mV beyond the supplies, limit the input current to 2mA. Internal Reference The MAX1084/MAX1085 have an on-chip voltage reference trimmed to 2.5V. The internal reference output is connected to REF and also drives the internal capacitive DAC. The output can be used as a reference voltage source for other components and can source up to 800A. Bypass REF with a 4.7F capacitor. Larger capacitors increase wake-up time when exiting shutdown (see Using SHDN to Reduce Supply Current). The internal reference is disabled in shutdown (SHDN = 0).
MAX1084/MAX1085
+3V to +5V
10F
0.1F 1 VDD AIN SCLK CS 8 7
ANALOG INPUT 0 TO VREF
2
SERIAL INTERFACE
SHUTDOWN INPUT
3 4 4.7F
MAX1084 MAX1085 SHDN DOUT
6 5
REF
GND
Figure 3. Typical Operating Circuit
GND CAPACITIVE DAC REF AIN CHOLD 12pF
ZERO RIN 800
COMPARATOR
CSWITCH* 6pF HOLD
TRACK
AUTOZERO RAIL *INCLUDES ALL INPUT PARASITICS
Figure 4. Equivalent Input Circuit
Serial Interface
Initialization After Power-Up and Starting a Conversion
When power is first applied, and if SHDN is not pulled low, it takes the fully discharged 4.7F reference bypass capacitor up to 1.4ms to acquire adequate charge for specified accuracy. No conversions should be performed during this time.
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400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference MAX1084/MAX1085
To start a conversion, pull CS low. At CS's falling edge, the T/H enters its hold mode and a conversion is initiated. Data can then be shifted out serially with the external clock. needed to shift out these bits. Extra clock pulses occurring after the conversion result has been clocked out, and prior to a rising edge of CS, produce trailing zeros at DOUT and have no effect on converter operation. Pull CS high after reading the conversion's LSB. For maximum throughput, CS can be pulled low again to initiate the next conversion immediately after the specified minimum time (tCS).
Using SHDN to Reduce Supply Current
Power consumption can be reduced significantly by shutting down the MAX1084/MAX1085 between conversions. Figure 6 shows a plot of average supply current vs. conversion rate. The wake-up time, tWAKE, is the time from SHDN deasserted to the time when a conversion may be initiated (Figure 5).This time depends on the time in shutdown (Figure 7) because the external 4.7F reference bypass capacitor loses charge slowly during shutdown and can be as long as 1.4ms.
Output Coding and Transfer Function
The data output from the MAX1084/MAX1085 is binary. Figure 10 depicts the nominal transfer function. Code transitions occur halfway between successive-integer LSB values; VREF = 2.5V, and 1LSB = 2.44mV or 2.5V / 1024.
Timing and Control
Conversion-start and data-read operations are controlled by the CS and SCLK digital inputs. The timing diagrams of Figures 8 and 9 outline serial-interface operation. A CS falling edge initiates a conversion sequence: the T/H stage holds the input voltage, the ADC begins to convert, and DOUT changes from high impedance to logic low. SCLK is used to drive the conversion process, and it shifts data out as each bit of conversion is determined. SCLK begins shifting out the data after the rising edge of the third SCLK pulse. DOUT transitions 20ns after each SCLK rising edge. The third rising clock edge produces the MSB of the conversion at DOUT, followed by the remaining bits. Since there are 12 data bits and 3 leading zeros, at least 15 rising clock edges are
Applications Information
Connection to Standard Interfaces
The MAX1084/MAX1085 serial interface is fully compatible with SPI, QSPI, and MICROWIRE (Figure 11). If a serial interface is available, set the CPU's serial interface in master mode so the CPU generates the serial clock. Choose a clock frequency up to 6.4MHz (MAX1084) or 4.8MHz (MAX1085). 1) Use a general-purpose I/O line on the CPU to pull CS low. Keep SCLK low. 2) Activate SCLK for a minimum of 13 clock cycles. The first two clocks produce zeros at DOUT. DOUT output data transitions 20ns after SCLK rising edge and is available in MSB-first format. Observe the SCLK-toDOUT valid timing characteristic. Data can be clocked into the P on SCLK's falling or rising edge.
COMPLETE CONVERSION SEQUENCE CS tWAKE SHDN
DOUT CONVERSION 0 POWERED UP POWERED DOWN CONVERSION 1 POWERED UP
Figure 5. Shutdown Sequence 10 ______________________________________________________________________________________
400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference MAX1084/MAX1085
SUPPLY CURRENT vs. CONVERSION RATE
10,000 REFERENCE POWER-UP DELAY (ms) VDD = 3.0V 1000 SUPPLY CURRENT (A) DOUT = FS RL = CL = 10pF 1.50 1.25 1.00 0.75 0.50 0.25 0 0.0001 CREF = 4.7F
100
10
1
0.1 0.1 1 10 100 1k 10k 100k CONVERSION RATE (SAMPLES)
0.001
0.01
0.1
1
10
TIME IN SHUTDOWN (s)
Figure 6. Supply Current vs. Conversion Rate
Figure 7. Reference Power-Up vs. Time in Shutdown
CS 1 SCLK DOUT HIGH-Z D9 ACQ A/D STATE HOLD/CONVERT ACQUISITION D8 D7 D6 D5 D4 D3 D23 D1 D0 S1 S0 HIGH-Z 3 4 8 12 15
Figure 8. Interface Timing Sequence
CS
tCSW ttCSO CSO tCSS tCL tCH tCSH tCSI
SCLK tCP tDOH tDOE DOUT tDOV tDOD
Figure 9. Detailed Serial-Interface Timing
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11
400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference MAX1084/MAX1085
OUTPUT CODE 11...111 11...110 11...101 FULL-SCALE TRANSITION
I/O SCK MISO +3V OR +5V
CS SCLK DOUT
MAX1084 MAX1085
FS = VREF - 1LSB 1LSB = VREF 1024 00...011 00...010 00...001 00...000 0 1 2 3 INPUT VOLTAGE (LSB) FS FS - 3/2LSB
SS a) SPI
CS SCK MISO +3V OR +5V
CS SCLK DOUT
SS b) QSPI
MAX1084 MAX1085
Figure 10. Unipolar Transfer Function, Full Scale (FS) = VREF 1LSB, Zero Scale (ZS) = GND
I/O
CS SCLK DOUT
3) Pull CS high at or after the 13th rising clock edge. If CS remains low, the two sub-bits and trailing zeros are clocked out after the LSB. 4) With CS = high, wait the minimum specified time, tCS, before initiating a new conversion by pulling CS low. If a conversion is aborted by pulling CS high before the conversion completes, wait the minimum acquisition time, tACQ, before starting a new conversion. CS must be held low until all data bits are clocked out. Data can be output in 2 bytes or continuously, as shown in Figure 8. The bytes contain the result of the conversion padded with three leading zeros, 2 sub-bits, and trailing zeros if SCLK is still active with CS kept low.
SK SI
MAX1084 MAX1085
c) MICROWIRE
Figure 11. Common Serial-Interface Connections to the MAX1084/MAX1085
SPI and Microwire
When using SPI or QSPI, set CPOL = 0 and CPHA = 0. Conversion begins with a CS falling edge. DOUT goes low, indicating a conversion is in progress. Two consecutive 1-byte reads are required to get the full 10+2 bits from the ADC. DOUT output data transitions on SCLK's rising edge and is clocked into the P on the following rising edge. The first byte contains 3 leading zeros, and 5 bits of conversion result. The second byte contains the remaining 5 bits, 2 sub-bits, and 1 trailing zero. See Figure 11 for connections and Figure 12 for timing.
the 10 bits of data from the ADC, QSPI allows the minimum number of clock cycles necessary to clock in the data. The MAX1084/MAX1085 require 13 clock cycles from the P to clock out the 10 bits of data. Additional clock cycles clock out the 2 sub-bits followed by trailing zeros. Figure 13 shows a transfer using CPOL = 0 and CPHA = 1. The result of conversion contains two zeros followed by the 10 bits of data in MSB-first format.
Layout and Grounding
For best performance, use PC boards. Wire-wrap boards are not recommended. Board layout should ensure that digital and analog signal lines are separated from each other. Do not run analog and digital (especially clock) lines parallel to one another, or digital lines underneath the ADC package. Figure 14 shows the recommended system ground connections. Establish a single-point analog ground ("star"
QSPI
Unlike SPI, which requires two 1-byte reads to acquire
12
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400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference
ground point) at GND, separate from the logic ground. Connect all other analog grounds and GND to this star ground point for further noise reduction. No other digital system ground should be connected to this single-point analog ground. The ground return to the power supply for this ground should be low impedance and as short as possible for noise-free operation. High-frequency noise in the VDD power supply may affect the ADC's high-speed comparator. Bypass this supply to the single-point analog ground with 0.1F and 10F bypass capacitors. Minimize capacitor lead lengths for best supply-noise rejection. To reduce the effect of supply noise, a 10 resistor can be connected as a lowpass filter to attenuate supply noise (Figure 14). static linearity parameters for the MAX1084/MAX1085 are measured using the endpoints method. Differential Nonlinearity Differential nonlinearity (DNL) is the difference between an actual step width and the ideal value of 1LSB. A DNL error specification of 1LSB or less guarantees no missing codes and a monotonic transfer function.
MAX1084/MAX1085
Aperture Jitter
Aperture jitter (tAJ) is the sample-to-sample variation in the time between the samples.
Aperture Delay
Aperture delay (tAD) is the time defined between the falling edge of CS and the instant when an actual sample is taken.
Definitions
Integral Nonlinearity Integral nonlinearity (INL) is the deviation of the values on an actual transfer function from a straight line. This straight line can be either a best-straight-line fit or a line drawn between the endpoints of the transfer function, once offset and gain errors have been nullified. The
Signal-to-Noise Ratio
For a waveform perfectly reconstructed from digital samples, signal-to-noise ratio (SNR) is the ratio of fullscale analog input (RMS value) to the RMS quantization error (residual error). The theoretical minimum analogto-digital noise is caused by quantization error and results directly from the ADC's resolution, (N bits):
CS
SCLK DOUT HIGH-Z
1
8
9
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
S1
S0
HIGH-Z
FIRST BYTE READ
SECOND BYTE READ
Figure 12. SPI/MICROWIRE Serial Interface Timing (CPOL = CPHA = 0)
CS
SCLK DOUT
1
12
14
HIGH-Z
HIGH-Z D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 S1 S0
Figure 13. QSPI Serial Interface Timing (CPOL = 0, CPHA = 1) ______________________________________________________________________________________ 13
400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference MAX1084/MAX1085
Effective Number of Bits
Effective number of bits (ENOB) indicates the global accuracy of an ADC at a specific input frequency and sampling rate. An ideal ADC's error consists of quantization noise only. With an input range equal to the fullscale range of the ADC, calculate the effective number of bits as follows: ENOB = (SINAD - 1.76) / 6.02
R* = 10 4.7F
SUPPLIES VDD VDD GND
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the RMS sum of the first five harmonics of the input signal to the fundamental itself. This is expressed as:
VDD DGND
0.1F VDD GND
MAX1084 MAX1085
*OPTIONAL
DIGITAL CIRCUITRY
THD = 20 x LOG
V2 + V3 + V4 + V5 V1
2
2
2
2
where V1 is the fundamental amplitude, and V2 through V5 are the amplitudes of the 2nd- through 5th-order harmonics, respectively.
Figure 14. Power-Supply Grounding Condition
Spurious-Free Dynamic Range
Spurious-free dynamic range (SFDR) is the ratio of RMS amplitude of the fundamental (maximum signal component) to the RMS value of the next-largest distortion component.
SNR = (6.02 N + 1.76)dB In reality, there are other noise sources besides quantization noise, including thermal noise, reference noise, clock jitter, etc. Therefore, SNR is computed by taking the ratio of the RMS signal to the RMS noise, which includes all spectral components minus the fundamental, the first five harmonics, and the DC offset.
___________________Chip Information
TRANSISTOR COUNT: 4286 PROCESS: BiCMOS
Signal-to-Noise Plus Distortion
Signal-to-noise plus distortion (SINAD) is the ratio of the fundamental input frequency's RMS amplitude to RMS equivalent of all other ADC output signals. SINAD (dB) = 20 log (SignalRMS / NoiseRMS)
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400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference
________________________________________________________________Package Information
SOICN.EPS
MAX1084/MAX1085
______________________________________________________________________________________
15
400ksps/300ksps, Single-Supply, Low-Power, Serial 10-Bit ADCs with Internal Reference MAX1084/MAX1085
NOTES
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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