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LTC2601/LTC2611/LTC2621 16-/14-/12-Bit Rail-to-Rail DACs in 10-Lead DFN
FEATURES
s
DESCRIPTIO
s s s s s s s s
Smallest Pin-Compatible Single DACs: LTC2601: 16 Bits LTC2611: 14 Bits LTC2621: 12 Bits Guaranteed Monotonic Over Temperature Wide 2.5V to 5.5V Supply Range Low Power Operation: 300A at 3V Power Down to 1A, Max High Rail-to-Rail Output Drive (15mA, Min) Double-Buffered Data Latches Asynchronous DAC Update Pin Tiny (3mm x 3mm) 10-Lead DFN Package
The LTC(R)2601/LTC2611/LTC2621 are single 16-, 14and 12-bit, 2.5V-to-5.5V rail-to-rail voltage output DACs in a 10-lead DFN package. They have built-in high performance output buffers and are guaranteed monotonic. These parts establish new board-density benchmarks for 16- and 14-bit DACs and advance performance standards for output drive, and load regulation in single-supply, voltage-output multiples. The parts use a simple SPI/MICROWIRETM compatible 3-wire serial interface which can be operated at clock rates up to 50MHz. Daisy-chain capability, hardware CLR and asynchronous DAC update (LDAC) pins are included. The LTC2601/LTC2611/LTC2621 incorporate a power-on reset circuit. During power-up, the voltage outputs rise less than 10mV above zero scale; and after power-up, they stay at zero scale until a valid write and update take place.
, LTC and LT are registered trademarks of Linear Technology Corporation. MICROWIRE is a trademark of National Semiconductor Corporation. U.S. patent number 5396245.
APPLICATIO S
s s s s
Mobile Communications Process Control and Industrial Automation Instrumentation Automatic Test Equipment
BLOCK DIAGRA
2 SDI
6 REF
9 VCC
3
SCK
INPUT REGISTER
DAC REGISTER
12-/14-/16-BIT DAC
7
DNL (LSB)
32-BIT SHIFT REGISTER
VOUT
5
CS/LD CONTROL DECODE LOGIC SDO LDAC 10 CLR 4 GND 8
1
2601 BD
U
Differential Nonlinearity (LTC2601)
1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 0 16384 32768 CODE 49152 65535
2600 G02
W
U
VCC = 5V VREF = 4.096V
2601f
1
LTC2601/LTC2611/LTC2621 ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART NUMBER
TOP VIEW SDO SDI SCK CLR CS/LD 1 2 3 4 5 11 10 LDAC 9 VCC 8 GND 7 VOUT 6 REF
Any Pin to GND ........................................... - 0.3V to 6V Any Pin to VCC .............................................- 6V to 0.3V Maximum Junction Temperature ......................... 125C Operating Temperature Range LTC2601C/LTC2611C/LTC2621C .......... 0C to 70C LTC2601I/LTC2611I/LTC2621I .......... - 40C to 85C Storage Temperature Range ................ - 65C to 125C Lead Temperature (Soldering, 10 sec)................ 300C
LTC2601CDD LTC2601IDD LTC2611CDD LTC2611IDD LTC2621CDD LTC2621IDD DD PART MARKING LAGT LBFQ LBFS
DD PACKAGE 10-LEAD (3mm x 3mm) PLASTIC DFN
TJMAX = 125C, JA = 43C/W EXPOSED PAD (PIN 11) IS GND MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. REF = 4.096V (VCC = 5V), REF = 2.048V (VCC = 2.5V), VOUT unloaded, unless otherwise noted.
SYMBOL PARAMETER Resolution Monotonicity DNL INL Integral Nonlinearity Load Regulation (Note 2) (Note 2) VREF = VCC = 5V, Midscale IOUT = 0mA to 15mA Sourcing IOUT = 0mA to 15mA Sinking VREF = VCC = 2.5V, Midscale IOUT = 0mA to 7.5mA Sourcing IOUT = 0mA to 7.5mA Sinking ZSE VOS Zero-Scale Error Offset Error VOS Temperature Coefficient GE Gain Error Gain Temperature Coefficient
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
q q q q q q q q q q
LTC2621 TYP MAX
MIN 14 14
LTC2611 TYP MAX
MIN 16 16
LTC2601 TYP MAX
UNITS Bits Bits
DC Performance 12 12 0.5 0.8 4 3 0.10 0.15 0.2 0.3 1 1.5 5 0.1 2 0.7
Differential Nonlinearity (Note 2)
1 16 0.5 0.5 1 1 9 9 13 0.45 0.60 0.9 1.2 1 1.5 5
1 64 2 2 4 4 9 9
0.03 0.125 0.04 0.125 0.06 0.08 1 1.5 5 0.03 0.7 2 0.25 0.25 9 9
LSB/mA LSB/mA LSB/mA LSB/mA mV mV V/C %FSR ppm/C
Code = 0 (Note 5)
0.05 0.7 2
2
U
LSB LSB
2601f
W
U
U
WW
W
LTC2601/LTC2611/LTC2621
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. REF = 4.096V (VCC = 5V), REF = 2.048V (VCC = 2.5V), VOUT unloaded, unless otherwise noted.
SYMBOL PSR ROUT ISC PARAMETER Power Supply Rejection DC Output Impedance Short-Circuit Output Current CONDITIONS VCC = 5V 10% VCC = 3V 10%
q
ELECTRICAL CHARACTERISTICS
LTC2601/LTC2611/LTC2621 MIN TYP MAX -80 -80 0.04 0.05 15 15 7.5 7.5 0 88 124 15
q
UNITS dB dB
VREF = VCC = 5V, Midscale; -15mA IOUT 15mA q VREF = VCC = 2.5V, Midscale; -7.5mA IOUT 7.5mA q VCC = 5.5V, VREF = 5.5V Code: Zero Scale; Forcing Output to VCC Code: Full Scale; Forcing Output to GND VCC = 2.5V, VREF = 2.5V Code: Zero Scale; Forcing Output to VCC Code: Full Scale; Forcing Output to GND
q q q q
0.15 0.15 60 60 50 50 VCC 160 1 5.5
mA mA mA mA V k pF A V mA mA A A V V
35 39 20 27
Reference Input Input Voltage Range Resistance Capacitance IREF VCC ICC Reference Current, Power Down Mode DAC Powered Down Positive Supply Voltage Supply Current For Specified Performance VCC = 5V (Note 3) VCC = 3V (Note 3) DAC Powered Down (Note 3) VCC = 5V DAC Powered Down (Note 3) VCC = 3V VCC = 2.5V to 5.5V VCC = 2.5V to 3.6V VCC = 4.5V to 5.5V VCC = 2.5V to 5.5V Load Current = -100A Load Current = +100A VIN = GND to VCC (Note 4) Power Supply
q q q q q q
Normal Mode
q
0.001 2.5 0.375 0.30 0.40 0.10 2.4 2.0
0.55 0.45 1 1
Digital I/O VIH VIL VOH VOL ILK CIN Digital Input High Voltage Digital Input Low Voltage Digital Output High Voltage Digital Output Low Voltage Digital Input Leakage Digital Input Capacitance
q q q q q q q q
0.8 0.6 VCC - 0.4 0.4 1 8
V V V V A pF
2601f
3
LTC2601/LTC2611/LTC2621
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. REF = 4.096V (VCC = 5V), REF = 2.048V (VCC = 2.5V), VOUT unloaded, unless otherwise noted.
SYMBOL PARAMETER AC Performance tS Settling Time (Note 6) 0.024% (1LSB at 12 Bits) 0.006% (1LSB at 14 Bits) 0.0015% (1LSB at 16 Bits) 0.024% (1LSB at 12 Bits) 0.006% (1LSB at 14 Bits) 0.0015% (1LSB at 16 Bits) 7 7 9 2.7 4.8 0.80 1000 12 180 120 100 15 7 9 10 2.7 4.8 5.2 0.80 1000 12 180 120 100 15 s s s s s s V/s pF nV * s kHz nV/Hz nV/Hz VP-P CONDITIONS MIN LTC2621 TYP MAX MIN LTC2611 TYP MAX MIN LTC2601 TYP MAX UNITS
ELECTRICAL CHARACTERISTICS
Settling Time for 1LSB Step (Note 7) Voltage Output Slew Rate Capacitive Load Driving Glitch Impulse Multiplying Bandwidth en Output Voltage Noise Density Output Voltage Noise
2.7
0.80 1000 At Midscale Transition At f = 1kHz At f = 10kHz 0.1Hz to 10Hz 12 180 120 100 15
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (See Figure 1) (Note 4)
SYMBOL PARAMETER VCC = 2.5V to 5.5V t1 SDI Valid to SCK Setup t2 SDI Valid to SCK Hold t3 SCK High Time t4 SCK Low Time t5 CS/LD Pulse Width t6 LSB SCK High to CS/LD High t7 CS/LD Low to SCK High t8 SDO Propagation Delay from SCK Falling Edge CONDITIONS
q q q q q q q
TI I G CHARACTERISTICS
t9 t10 t12 t13
Note 1: Absolute maximum ratings are those values beyond which the life of a device may be impaired. Note 2: Linearity and monotonicity are defined from code kL to code 2N - 1, where N is the resolution and kL is given by kL = 0.016(2N/VREF), rounded to the nearest whole code. For VREF = 4.096V and N = 16, kL = 256 and linearity is defined from code 256 to code 65,535. Note 3: Digital inputs at 0V or VCC. Note 4: Guaranteed by design and not production tested.
4
UW
LTC2601/LTC2611/LTC2621 MIN TYP MAX 4 4 9 9 10 7 7 20 45 20 7 15 200 50
UNITS ns ns ns ns ns ns ns ns ns ns ns ns ns MHz
CLOAD = 10pF VCC = 4.5V to 5.5V VCC = 2.5V to 5.5V
q q q q q q
CLR Pulse Width CS/LD High to SCK Positive Edge LDAC Pulse Width CS/LD High to LDAC High or Low Transition SCK Frequency
50% Duty Cycle
q
Note 5: Inferred from measurement at code KL = 0.016(2N/VREF) and at full scale. Note 6: VCC = 5V, VREF = 4.096V. DAC is stepped 1/4 scale to 3/4 scale and 3/4 scale to 1/4 scale. Load is 2k in parallel with 200pF to GND. Note 7: VCC = 5V, VREF = 4.096V. DAC is stepped 1LSB between half scale and half scale - 1. Load is 2k in parallel with 200pF to GND.
2601f
LTC2601/LTC2611/LTC2621 TYPICAL PERFOR A CE CHARACTERISTICS
LTC2601
Integral Nonlinearity (INL)
32 24 16 DNL (LSB) INL (LSB) 8 0 -8 -16 -24 -32 0 16384 32768 CODE 49152 65535
2601 G01
VCC = 5V VREF = 4.096V
0 -0.2 -0.4 -0.6 -0.8 -1.0 0 16384 32768 CODE 49152 65535
2600 G02
INL (LSB)
DNL vs Temperature
1.0 0.8 0.6 16 0.4 DNL (POS) 8 0 -8 -16 -0.6 -0.8 -1.0 -50 -30 -10 10 30 50 TEMPERATURE (C) 70 90 -24 -32 VCC = 5V VREF = 4.096V 32 24
DNL (LSB)
0 -0.2 -0.4 DNL (NEG)
DNL (LSB)
INL (LSB)
0.2
Settling to 1LSB
VOUT 100V/DIV 9.7s CS/LD 2V/DIV
VCC = 5V, VREF = 4.096V 1/4-SCALE TO 3/4-SCALE STEP RL = 2k, CL = 200pF AVERAGE OF 2048 EVENTS
UW
2601 G04
Differential Nonlinearity (DNL)
1.0 0.8 0.6 0.4 0.2 16 8 0 -8 -16 -24 VCC = 5V VREF = 4.096V 32 24
INL vs Temperature
VCC = 5V VREF = 4.096V
INL (POS)
INL (NEG)
-32 -50
-30
-10 10 30 50 TEMPERATURE (C)
70
90
2601 G03
INL vs VREF
VCC = 5.5V 1.5 1.0 INL (POS) 0.5
DNL vs VREF
VCC = 5.5V
DNL (POS) 0 DNL (NEG) -0.5 -1.0 -1.5
INL (NEG)
0
1
2 3 VREF (V)
4
5
2601 G05
0
1
2 3 VREF (V)
4
5
2601 G06
Settling of Full-Scale Step
VOUT 100V/DIV
12.3s
CS/LD 2V/DIV
2s/DIV
2601 G07
5s/DIV SETTLING TO 1LSB VCC = 5V, VREF = 4.096V CODE 512 TO 65535 STEP AVERAGE OF 2048 EVENTS
2601 G08
2601f
5
LTC2601/LTC2611/LTC2621 TYPICAL PERFOR A CE CHARACTERISTICS
LTC2611
Integral Nonlinearity (INL)
8 6 4 0.4 DNL (LSB) INL (LSB) 2 0 -2 -4 -0.6 -6 -8 0 4096 8192 CODE 12288 16383
2601 G09
VCC = 5V VREF = 4.096V
LTC2621
Integral Nonlinearity (INL)
2.0 1.5 1.0 0.4 DNL (LSB) INL (LSB) 0.5 0 -0.5 -1.0 -0.6 -1.5 -2.0 0 1024 2048 CODE 3072 4095
2601 G12
VCC = 5V VREF = 4.096V
LTC2601/LTC2611/LTC2621
Current Limiting
0.10 0.08 0.06 0.04
VOUT (V)
CODE = MIDSCALE VREF = VCC = 5V VREF = VCC = 3V
OFFSET ERROR (mV)
VOUT (mV)
0.02 0 -0.02 -0.04 -0.06 -0.08 -0.10 10 -40 -30 -20 -10 0 IOUT (mA) 20 30 40 VREF = VCC = 3V VREF = VCC = 5V
6
UW
Differential Nonlinearity (DNL)
1.0 0.8 0.6
VOUT 100V/DIV
Settling to 1LSB
VCC = 5V VREF = 4.096V
0.2 0 -0.2 -0.4
CS/LD 2V/DIV
8.9s 2s/DIV VCC = 5V, VREF = 4.096V 1/4-SCALE TO 3/4-SCALE STEP RL = 2k, CL = 200pF AVERAGE OF 2048 EVENTS
2601 G11
-0.8 -1.0 0 4096 8192 CODE 12288 16383
2601 G10
Differential Nonlinearity (DNL)
1.0 0.8 0.6 VCC = 5V VREF = 4.096V
Settling to 1LSB
6.8s VOUT 1mV/DIV
0.2 0 -0.2 -0.4
CS/LD 2V/DIV
2s/DIV VCC = 5V, VREF = 4.096V 1/4-SCALE TO 3/4-SCALE STEP RL = 2k, CL = 200pF AVERAGE OF 2048 EVENTS
2601 G14
-0.8 -1.0 0 1024 2048 CODE 3072 4095
2601 G13
Load Regulation
1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -35 -25 -15 -5 5 IOUT (mA) 15 25 35 VREF = VCC = 3V VREF = VCC = 5V 2 1 0 -1 -2 CODE = MIDSCALE 3
Offset Error vs Temperature
-3 -50
-30
-10 10 30 50 TEMPERATURE (C)
70
90
2601 G17
2601 G18
2601 G19
2601f
LTC2601/LTC2611/LTC2621 TYPICAL PERFOR A CE CHARACTERISTICS
LTC2601/LTC2611/LTC2621
Zero-Scale Error vs Temperature
3 2.5 ZERO-SCALE ERROR (mV) GAIN ERROR (%FSR) 2.0 1.5 1.0 0.5 0 -50 0.4 0.3 OFFSET ERROR (mV) -30 -10 10 30 50 TEMPERATURE (C) 70 90 0.2 0.1 0 -0.1 -0.2 -0.3 -30 -10 10 30 50 TEMPERATURE (C) 70 90 -0.4 -50 -2 -3
Gain Error vs VCC
0.4 0.3 0.2
450 400 350 300 ICC (nA) 250 200 150
GAIN ERROR (%FSR)
0.1 0 -0.1 -0.2
-0.3 -0.4 2.5 3 3.5 4 VCC (V) 4.5 5 5.5
2601 G23
Midscale Glitch Impulse
VOUT 10mV/DIV 12nV-s TYP
VOUT (V)
CS/LD 5V/DIV
2601 G26
2.5s/DIV
UW
2601 G20
Gain Error vs Temperature
3 2 1 0 -1
Offset Error vs VCC
2.5
3
3.5
4 VCC (V)
4.5
5
5.5
2601 G22
2601 G21
ICC Shutdown vs VCC
Large-Signal Response
VOUT 0.5V/DIV
VREF = VCC = 5V 1/4-SCALE TO 3/4-SCALE 2.5s/DIV
2601 G25
100 50 0 2.5 3 3.5 4 VCC (V) 4.5 5 5.5
2601 G24
Power-On Reset Glitch
5.0 4.5 4.0
VCC 1V/DIV
Headroom at Rails vs Output Current
5V SOURCING
3.5 3.0 2.5 2.0 1.5 1.0
250s/DIV
2601 G27
3V SOURCING
4mV PEAK VOUT 10mV/DIV
5V SINKING 3V SINKING
0.5 0 0 1 2 3
456 IOUT (mA)
7
8
9
10
2601 G28
2601f
7
LTC2601/LTC2611/LTC2621 TYPICAL PERFOR A CE CHARACTERISTICS
LTC2601/LTC2611/LTC2621
Supply Current vs Logic Voltage
2.4 2.3 2.2 2.1 ICC (mA) 2.0 1.9 1.8 1.7 1.6 1.5 0 0.5 1 1.5 2 2.5 3 3.5 LOGIC VOLTAGE (V) 4 4.5 5 VCC = 5V SWEEP SCK, SDI AND CS/LD 0V TO VCC
Multiplying Bandwidth
0 -3 -6 -9 -12 -15
dB
-18 -21 -24 -27 -30 -33 -36 VCC = 5V VREF (DC) = 2V VREF (AC) = 0.2VP-P CODE = FULL SCALE 1k 10k 100k FREQUENCY (Hz) 1M
2601 G32
Short-Circuit Output Current vs VOUT (Sinking)
0mA
10mA/DIV
0mA
VCC = 5.5V VREF = 5.6V CODE = 0 VOUT SWEPT 0V TO VCC 1V/DIV
2601 G18
10mA/DIV
8
UW
Hardware CLR
VOUT 1V/DIV
CLR 5V/DIV 1s/DIV
2601 G31
2601 G29
Output Voltage Noise, 0.1Hz to 10Hz
VOUT 10V/DIV
0
1
2
3
456 SECONDS
7
8
9
10
2601 G33
Short-Circuit Output Current vs VOUT (Sourcing)
VCC = 5.5V VREF = 5.6V CODE = FULL SCALE VOUT SWEPT VCC TO 0V 1V/DIV
2600 G19
2601f
LTC2601/LTC2611/LTC2621
PIN FUNCTIONS
SDO (Pin 1): Serial Interface Data Output. The serial output of the shift register appears at the SDO pin. The data transferred to the device via the SDI pin is delayed 32 SCK rising edges before being output at the next falling edge. This pin is used for daisy-chain operation. SDI (Pin 2): Serial Interface Data Input. Data is applied to SDI for transfer to the device at the rising edge of SCK (Pin 3). The LTC2601 accepts input word lengths of either 24 or 32 bits. SCK (Pin 3): Serial Interface Clock Input. CMOS and TTL compatible. CLR (Pin 4): Asynchronous Clear Input. A logic low at this level-triggered input clears all registers and causes the DAC voltage outputs to drop to 0V. CMOS and TTL compatible. CS/LD (Pin 5): Serial Interface Chip Select/Load Input. When CS/LD is low, SCK is enabled for shifting data on SDI into the register. When CS/LD is taken high, SCK is disabled and the specified command (see Table 1) is executed. REF (Pin 6): Reference Voltage Input. 0V VREF VCC. VOUT (Pin 7): DAC Analog Voltage Output. The output range is 0V to VREF. GND (Pin 8): Analog Ground. VCC (Pin 9): Supply Voltage Input. 2.5V VCC 5.5V. LDAC (Pin 10): Asynchronous DAC Update Pin. If CS/LD is high, a falling edge on LDAC immediately updates the DAC register with the contents of the input register (similar to a software update). If CS/LD is low when LDAC goes low, the DAC register is updated after CS/LD returns high. A low on the LDAC pin powers up the DAC. A software power down command is ignored if LDAC is low. Exposed Pad (Pin 11): Ground. Must be soldered to PCB ground.
U
U
U
2601f
9
LTC2601/LTC2611/LTC2621
BLOCK DIAGRA
2 SDI
3
SCK
5
CS/LD CONTROL DECODE LOGIC SDO LDAC 10 CLR 4 GND 8
1
TI I G DIAGRA S
t1 t2 SCK 1 t3 2 t4 3 23 t6 24 t10 SDI t5 CS/LD t8 SDO t13 LDAC
2601 F01a
10
W
W
6 REF 9 VCC 32-BIT SHIFT REGISTER INPUT REGISTER DAC REGISTER 12-/14-/16-BIT DAC VOUT 7
2601 BD
UW
t7
t12
Figure 1a
CS/LD t13 LDAC
2601 F01b
Figure 1b
2601f
LTC2601/LTC2611/LTC2621
OPERATIO
Power-On Reset
The LTC2601/LTC2611/LTC2621 clear the outputs to zero scale when power is first applied, making system initialization consistent and repeatable. For some applications, downstream circuits are active during DAC power-up, and may be sensitive to nonzero outputs from the DAC during this time. The LTC2601/ LTC2611/LTC2621 contain circuitry to reduce the poweron glitch; furthermore, the glitch amplitude can be made arbitrarily small by reducing the ramp rate of the power supply. For example, if the power supply is ramped to 5V in 1ms, the analog outputs rise less than 10mV above ground (typ) during power-on. See Power-On Reset Glitch in the Typical Performance Characteristics section. Power Supply Sequencing The voltage at REF (Pin 6) should be kept within the range - 0.3V VREF VCC + 0.3V (see Absolute Maximum Ratings). Particular care should be taken to observe these limits during power supply turn-on and turn-off sequences, when the voltage at VCC (Pin 16) is in transition. Transfer Function The digital-to-analog transfer function is: k VOUT(IDEAL) = N VREF 2 where k is the decimal equivalent of the binary DAC input code, N is the resolution and VREF is the voltage at REF (Pin 6). Serial Interface The CS/LD input is level triggered. When this input is taken low, it acts as a chip-select signal, powering-on the SDI and SCK buffers and enabling the input shift register. Data (SDI input) is transferred at the next 24 rising SCK edges. The 4-bit command, C3-C0, is loaded first; then 4 don't care bits; and finally the 16-bit data word. The data word comprises the 16-, 14- or 12-bit input code, ordered MSBto-LSB, followed by 0, 2 or 4 don't care bits (LTC2601, LTC2611 and LTC2621 respectively). Data can only be transferred to the device when the CS/LD signal is low.The rising edge of CS/LD ends the data transfer and causes the
U
device to execute the command specified in the 24-bit input word. The complete sequence is shown in Figure 2a. The command (C3-C0) assignments are shown in Table 1. The first four commands in the table consist of write and update operations. A write operation loads a 16-bit data word from the 32-bit shift register into the input register of the DAC. In an update operation, the data word is copied from the input register to the DAC register and converted to an analog voltage at the DAC output. The update operation also powers up the DAC if it had been in powerdown mode. The data path and registers are shown in the Block Diagram. While the minimum input word is 24 bits, it may optionally be extended to 32 bits. To use the 32-bit word width, 8 don't-care bits are transferred to the device first, followed by the 24-bit word as just described. Figure 2b shows the 32-bit sequence. The 32-bit word is required for daisy-chain operation, and is also available to accommodate microprocessors which have a minimum word width of 16 bits (2 bytes). Daisy-Chain Operation The serial output of the shift register appears at the SDO pin. Data transferred to the device from the SDI input is delayed 32 SCK rising edges before being output at the next SCK falling edge. The SDO output can be used to facilitate control of multiple serial devices from a single 3-wire serial port (i.e., SCK, SDI and CS/LD). Such a "daisy chain" series is configured by connecting SDO of each upstream device to SDI of the next device in the chain. The shift registers of the devices are thus connected in series, effectively forming a single input shift register which extends through the entire chain.
Table 1.
COMMAND* C3 C2 C1 C0 0 0 0 0 1 0 0 0 1 1 0 0 1 0 1 0 1 1 0 1 Write to Input Register Update (Power Up) DAC Register Write to and Update (Power Up) Power Down No Operation
2601f
*Command codes not shown are reserved and should not be used.
11
LTC2601/LTC2611/LTC2621
OPERATIO
INPUT WORD (LTC2601)
COMMAND C3 C2 C1 C0 DON'T CARE BITS X X X X DATA (16 BITS) D15 D14 D13 D12 D11 D10 D9 MSB D8 D7 D6 D5 D4 D3 D2 D1 D0 LSB
2601 TBL01
INPUT WORD (LTC2611)
COMMAND C3 C2 C1 C0 DON'T CARE BITS X X X X DATA (14 BITS + 2 DON'T CARE BITS) D13 D12 D11 D10 D9 MSB D8 D7 D6 D5 D4 D3 D2 D1 D0 LSB
2601 TBL02
INPUT WORD (LTC2621)
COMMAND C3 C2 C1 C0 DON'T CARE BITS X X X X D11 D10 D9 MSB DATA (12 BITS + 4 DON'T CARE BITS) D8 D7 D6 D5 D4 D3 D2 D1 D0 LSB
2601 TBL03
Because of this, the devices can be addressed and controlled individually by simply concatenating their input words; the first instruction addresses the last device in the chain and so forth. The SCK and CS/LD signals are common to all devices in the series. In use, CS/LD is first taken low. Then the concatenated input data is transferred to the chain, using SDI of the first device as the data input. When the data transfer is complete, CS/LD is taken high, which executes the commands specified for each of the devices simultaneously. A single device can be controlled by using the no-operation command (1111) for the other devices in the chain. Power-Down Mode For power-constrained applications, power-down mode can be used to reduce the supply current whenever the DAC output is not needed. When in power-down, the buffer amplifier, bias circuit and reference input is disabled and draws essentially zero current. The DAC output is put into a high impedance state, and the output pin is passively pulled to ground through 90k resistors. Inputand DAC-register contents are not disturbed during powerdown. The DAC can be put into power-down mode by using command 0100b. The 16-bit data word is ignored. The supply and reference currents are reduced to almost zero when the DAC is powered down; the effective resistance at
12
U
X X
X
X
X
X
REF rises accordingly becoming a high impedance input (typically > 1G). Normal operation can be resumed by executing any command which includes a DAC update, as shown in Table 1 or performing an asynchronous update (LDAC) as described in the next section. The DAC is powered up as its voltage output is updated. When the DAC in powereddown state is powered up and updated, normal settling is delayed. The main bias generation circuit block has been automatically shut down in addition to the DAC amplifier and reference input and so the power up delay time is 12s (for VCC = 5V) or 30s (for VCC = 3V). Asynchronous DAC Update Using LDAC In addition to the update commands shown in Table 1, the LDAC pin asynchronously updates the DAC register with the contents of the input register. If CS/LD is high, a low on the LDAC pin causes the DAC register to be updated with the contents of the input register. If CS/LD is low, a low going pulse on the LDAC pin before the rising edge of CS/LD powers up the DAC but does not cause the output to be updated. If LDAC remains low after the rising edge of CS/LD, then LDAC is recognized, the command specified in the 24-bit word just transferred is executed and the DAC output is updated.
2601f
LTC2601/LTC2611/LTC2621
OPERATIO
The DAC is powered up when LDAC is taken low, independent of the state of CS/LD. If LDAC is low at the time CS/LD goes high, it inhibits any software power-down command that was specified in the input word. Voltage Outputs The rail-to-rail amplifier contained in these parts has guaranteed load regulation when sourcing or sinking up to 15mA at 5V (7.5mA at 3V). Load regulation is a measure of the amplifier's ability to maintain the rated voltage accuracy over a wide range of load conditions. The measured change in output voltage per milliampere of forced load current change is expressed in LSB/mA. DC output impedance is equivalent to load regulation, and may be derived from it by simply calculating a change in units from LSB/mA to Ohms. The amplifier's DC output impedance is 0.05 when driving a load well away from the rails. When drawing a load current from either rail, the output voltage headroom with respect to that rail is limited by the 25 typical channel resistance of the output devices; e.g., when sinking 1mA, the minimum output voltage = 25 * 1mA = 25mV. See the graph Headroom at Rails vs Output Current in the Typical Performance Characteristics section. The amplifier is stable driving capacitive loads of up to 1000pF. Board Layout The excellent load regulation of these devices is achieved in part by keeping "signal" and "power" grounds separated internally and by reducing shared internal resistance. The GND pin functions both as the node to which the reference and output voltages are referred and as a return path for power currents in the device. Because of this,
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careful thought should be given to the grounding scheme and board layout in order to ensure rated performance. The PC board should have separate areas for the analog and digital sections of the circuit. This keeps digital signals away from sensitive analog signals and facilitates the use of separate digital and analog ground planes which have minimal capacitive and resistive interaction with each other. Digital and analog ground planes should be joined at only one point, establishing a system star ground as close to the device's ground pin as possible. Ideally, the analog ground plane should be located on the component side of the board, and should be allowed to run under the part to shield it from noise. Analog ground should be a continuous and uninterrupted plane, except for necessary lead pads and vias, with signal traces on another layer. The GND pin of the part should be connected to analog ground. Resistance from the GND pin to system star ground should be as low as possible. Resistance here will add directly to the effective DC output impedance of the device (typically 0.05). Note that the LTC2601/LTC2611/ LTC2621 are no more susceptible to these effects than other parts of their type; on the contrary, they allow layout-based performance improvements to shine rather than limiting attainable performance with excessive internal resistance. Rail-to-Rail Output Considerations In any rail-to-rail voltage output device, the output is limited to voltages within the supply range. Since the analog output of the device cannot go below ground, it may limit for the lowest codes as shown in Figure 3b. Similarly, limiting can occur near full scale when the REF pin is tied to VCC. If VREF = VCC and the DAC full-scale error (FSE) is positive, the output for the highest codes limits at VCC as shown in Figure 3c. No full-scale limiting can occur if VREF is less than VCC - FSE. Offset and linearity are defined and tested over the region of the DAC transfer function where no output limiting can occur.
2601f
13
OPERATIO
COMMAND WORD
4 DON'T CARE BITS
DATA WORD
24-BIT INPUT WORD
LTC2601/LTC2611/LTC2621
Figure 2a. LTC2601 24-Bit Load Sequence (Minimum Input Word). LTC2611 SDI Data Word: 14-Bit Input Code + 2 Don't-Care Bits; LTC2621 SDI Data Word: 12-Bit Input Code + 4 Don't-Care Bits
CS/LD 6 7 13 14 17 D15 D14 D13 D12 D11 D10 X X X X 4 DON'T CARE BITS C0 X X X X D15 D14 D13 D12 D11 D10 D9 X COMMAND WORD X X X C3 C2 C1 X C3 C2 C1 C0 8 9 10 21 11 12 18 16 20 15 19 X 22 23 D9 24 D8 25 D7 DATA WORD D8 D7 D6 D5 D4 D3 D2 D1 D0 26 D6 27 D5 28 D4 29 D3 30 D2 31 D1 32 D0
SCK
1
2
3
4
5
SDI
X
X
X
X
X
DON'T CARE
SDO
X
X
X
X
X
PREVIOUS 32-BIT INPUT WORD t1 t2 SCK 17 t3 SDI SDO D15 t8 PREVIOUS D15 PREVIOUS D14 t4 D14 18
CURRENT 32-BIT INPUT WORD
2601 F02b
Figure 2b. LTC2601 32-Bit Load Sequence (Required for Daisy-Chain Operation). LTC2611 SDI/SDO Data Word: 14-Bit Input Code + 2 Don't-Care Bits; LTC2621 SDI/SDO Data Word: 12-Bit Input Code + 4 Don't-Care Bits
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14
1 2 7 13 14 17 D7
2601 F02a
CS/LD 3 4 10 21 D3 D2 D1 D0 23 D14 D13 D12 D11 D10 D9 D8 D6 D5 D4 11 12 18 24 22 16 20 C0 X X X X D15 5 6 8 9 15 19 C1
SCK C2
SDI
C3
2601f
LTC2601/LTC2611/LTC2621
OPERATIO U
VREF = VCC POSITIVE FSE VREF = VCC OUTPUT VOLTAGE OUTPUT VOLTAGE INPUT CODE (c)
2601 F03
OUTPUT VOLTAGE 0 32, 768 INPUT CODE (a) 65, 535
0V NEGATIVE OFFSET INPUT CODE (b)
Figure 3. Effects of Rail-to-Rail Operation On the DAC Transfer Curve. (a) Overall Transfer Function (b) Effect of Negative Offset for Codes Near Zero Scale (c) Effect of Positive Full-Scale Error for Codes Near Full Scale
PACKAGE DESCRIPTIO
3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.38 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE PIN 1 TOP MARK (SEE NOTE 6)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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DD Package 10-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115 TYP 6 0.675 0.05 0.38 0.10 10 3.00 0.10 (4 SIDES) 1.65 0.10 (2 SIDES)
(DD10) DFN 1103
5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES)
1
0.25 0.05 0.50 BSC
0.00 - 0.05
BOTTOM VIEW--EXPOSED PAD
2601f
15
LTC2601/LTC2611/LTC2621
TYPICAL APPLICATIO
Demo Circuit DC777 Schematic. Onboard 20-Bit ADC Measures Key Performance Parameters
5V 0.1F 9 6 LDAC VCC VREF CLR SDI LTC2601 VOUT SCK CS/LD SDO GND 8 VREF 1V TO 5V 2 FSSET 7 100 7.5k 100pF DAC OUTPUT ZSSET GND 5 6 3 VIN 1 VCC 5V 0.1F
10 4 2 3 5 1 SPI BUS
RELATED PARTS
PART NUMBER LTC1458/LTC1458L LTC1654 LTC1655/LTC1655L LTC1657/LTC1657L LTC1660/LTC1665 LTC1661 LTC1662 LTC1663 LTC1664 LTC1669 LTC1821 LTC2600/LTC2610 LTC2620 LTC2602/LTC2612 LTC2622 LTC2604/LTC2614 LTC2624 DESCRIPTION Quad 12-Bit Rail-to-Rail Output DACs with Added Functionality Dual 14-Bit Rail-to-Rail VOUT DAC Single 16-Bit VOUT DACs with Serial Interface in SO-8 Parrallel 5V/3V 16-Bit VOUT DACs Octal 10/8-Bit VOUT DACs in 16-Pin Narrow SSOP Dual 10-Bit VOUT DAC 8-Lead MSOP Dual 10-Bit VOUT DAC 8-Lead MSOP Single 10-Bit VOUT DAC in SOT-23 Quad 10-Bit VOUT DAC 16-Lead SSOP Single 10-Bit VOUT DAC 5-Lead SOT-23 Parallel 16-Bit Voltage Output DAC Octal 16-/14-/12-Bit VOUT DACs in 16-Lead SSOP Dual 16-/14-/12-Bit VOUT DACs in 8-Lead MSOP Quad 16-/14-/12-Bit VOUT DACs in 16-Lead SSOP COMMENTS LTC1458: VCC = 4.5V to 5.5V, VOUT = 0V to 4.096V LTC1458L: VCC = 2.7V to 5.5V, VOUT = 0V to 2.5V Programmable Speed/Power, 3.5s/750A, 8s/450A VCC = 5V(3V), Low Power, Deglitched Low Power, Deglitched, Rail-to-Rail VOUT VCC = 2.7V to 5.5V, Micropower, Rail-to-Rail Output Micropower Rail-to-Rail Output, 3-Wire Interface Ultralow Power, Rail-to-Rail Output SMBus Interface, Pin-for-Pin Compatible with LTC1669 Micropower Rail-to-Rail Output, 3-Wire Interface Pin-for-Pin Compatible with LTC1663 Precision 16-Bit Settling in 2s for 10V Step 250A per DAC, 2.5V to 5.5V Supply Range, Rail-to-Rail Output 300A per DAC, 2.5V to 5.5V Supply Range, Rail-to-Rail Output 250A per DAC, 2.5V to 5.5V Supply Range, Rail-to-Rail Output
16 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
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LTC2421 9 SCK 8 SDO 7 CS 10 FO
2601 TA01
2601f LT/TP 0404 1K * PRINTED IN THE USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2004

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