Data Sheet
LTC2688
16-Channel, 16-Bit Voltage Output SoftSpan DAC
FEATURES
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FUNCTIONAL BLOCK DIAGRAM
16 independent SoftSpan DACs
Independently programmable output ranges: 0 V to 5 V, 0 V to
10 V, ±5 V, ±10 V, ±15 V
Full 16-bit resolution at all ranges
Flexible single- or dual-supply operation
Maximum INL error: ±3 LSB
Precision 4.096 V reference, ±5 ppm/°C maximum
A/B toggle or sinusoidal dither using up to 3 toggle pins
Multiplexer for output voltage and load current sense
Outputs drive ±20 mA guaranteed
6 mm × 6 mm, 40-lead LFCSP
APPLICATIONS
Optical networking
Instrumentation
► Data acquisition
► Automatic test equipment
► Process control and industrial automation
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Figure 1.
GENERAL DESCRIPTION
The LTC2688 is a 16-channel,16-bit, ±15 V digital-to-analog converter (DAC) with an integrated precision reference. The LTC2688
is guaranteed monotonic and has built in rail-to-rail output buffers
that can source or sink up to 20 mA. This SoftSpan™ DAC offers
five output ranges up to ±15 V. The range of each channel is
independently programmable.
The internal 4.096 V precision reference sets the accuracy of the
output voltage. An external reference can be used for additional
range options. Three toggle pins support Input Register A and Input
Register B toggle or sinusoidal dither at multiple frequencies. An
analog multiplexer simplifies measurement of pin voltages, load
currents, and junction temperature.
Programmable offset and gain registers improve the accuracy of
the DAC outputs.
The serial peripheral interface (SPI) and MICROWIRE™-compatible, 3-wire serial interface operates on logic levels as low as 1.71 V
and clock rates up to 50 MHz.
Rev. 0
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Data Sheet
LTC2688
TABLE OF CONTENTS
Features................................................................ 1
Applications........................................................... 1
Functional Block Diagram......................................1
General Description...............................................1
Specifications........................................................ 3
Timing Characteristics........................................6
Absolute Maximum Ratings...................................7
Thermal Resistance........................................... 7
ESD Caution.......................................................7
Pin Configuration and Function Descriptions........ 8
Typical Performance Characteristics................... 10
Terminology......................................................... 17
Theory of Operation.............................................18
Power-On Reset...............................................18
Power Supply Sequencing............................... 18
Serial Interface................................................. 19
Writing Codes to DACs.................................... 21
Span Selection and Channel Settings..............22
Read Commands............................................. 22
Offset and Gain Adjustment............................. 23
Analog Mux...................................................... 25
Toggle and Dither Operation............................ 26
Daisy-Chain Mode............................................33
Power-Down Mode...........................................33
Asynchronous DAC Update Using LDAC.........35
Fault Detection................................................. 35
Configuration Register......................................36
Reference Modes............................................. 36
Voltage Outputs................................................36
Thermal Overload Protection........................... 37
Applications Information...................................... 38
Printed Circuit Board Layout............................ 38
Command Addresses.......................................... 39
Outline Dimensions............................................. 41
Ordering Guide.................................................41
Evaluation Boards............................................ 42
REVISION HISTORY
6/2021—Revision 0: Initial Version
analog.com
Rev. 0 | 2 of 42
Data Sheet
LTC2688
SPECIFICATIONS
All specifications apply over the full operating temperature range, unless otherwise noted. Typical values are at TA = 25°C. VCC = 5 V, IOVCC =
5 V, V1+ = V2+ = 15 V, V− = −15 V, VREF = 4.096 V, VOUT unloaded, unless otherwise specified. For ±15 V range, V1+ = V2+ = 18 V, V− = −18 V.
Table 1.
Parameter
DC PERFORMANCE
Resolution
Monotonicity
Differential Nonlinearity
Integral Nonlinearity
Unipolar Offset Error
VOS Temperature Coefficient
Single-Supply Zero-Scale Error
Bipolar Zero Error
BZE Temperature Coefficient
Gain Error
Gain Temperature Coefficient
Output Voltage Swing
Power Supply Rejection
Symbol
DNL
INL
VOS
ZSE
BZE
GE
VOUT
PSR
Load Regulation
DC Crosstalk3, 0 V to 5 V Range
Vx+/V− Short-Circuit Output Current4, ±15 V
Output Range
ISC
Test Conditions/Comments
All ranges1
All ranges1
All ranges1
0 V to 5 V range
0 V to 10 V range
All unipolar ranges
All unipolar ranges, V− = GND
All bipolar ranges
All bipolar ranges
All ranges, external reference
To V− (unloaded)
To Vx+ (unloaded)
To V− (−20 mA ≤ output current (IOUT) ≤
+20 mA), ±15 V range
To Vx+ (−20 mA ≤ IOUT ≤ +20 mA), ±15 V
range
VCC = 5 V ± 5%
Vx+/V− = 15 V ± 5%
−20 mA ≤ IOUT ≤ +20 mA, Vx+ = +17.2 V, V− =
−17.2 V, ±15 V range
Due to full-scale output change
Due to load current change
Due to powering down (per channel)
Negative full scale, forcing output to GND
Min
Typ
TA = TMIN to TMAX
Reference Temperature Coefficient6
Line Regulation
Short-Circuit Current
REFCOMP Pin Short-Circuit Current
Load Regulation
Output Voltage Noise Density
REFERENCE INPUT
Range
Current
Capacitance
POWER SUPPLY
Analog Supply Voltage
Analog Positive Supply
±0.5
±1
1
2
analog.com
4
±0.04
±0.08
2
V− + 0.004
Vx+ − 0.004
V− + 2.2
Vx+ − 2.2
−80
−80
70
dB
dB
μV/mA
150
±2
±1
±4
μV
μV/mA
μV
mA
−41
4.094
4.092
4.096
4.096
±2
−80
0.1
10
320
32
2.0
4.75
VCC – 0.3
Bits
Bits
LSB
LSB
mV
mV
ppm/°C
mV
% FSR2
ppm/°C
% FSR2
ppm/°C
V
V
V
V
10
8
VCC
V1+
±1
±3
±2
±4
2
VCC ± 5%
Forcing output to GND
Forcing output to GND
IOUT = 1 μA
REFCOMP, capacitor (CREFCOMP) = REF
capacitor (CREF) = 0.1 μF, at f = 10 kHz
External reference mode7
Unit
16
16
Positive full scale, forcing output to GND
REFERENCE
Reference Output Voltage5
Max
41
mA
4.098
4.100
±5
V
V
ppm/°C
dB
mA
μA
mV/mA
nV/√Hz
VCC – 0.6
15
V
μA
pF
5.25
V– + 42
V
V
Rev. 0 | 3 of 42
Data Sheet
LTC2688
SPECIFICATIONS
Table 1.
Parameter
Analog Negative Supply
Digital Input/Output (I/O) Supply Voltage
Supply Current
VCC8
Vx+/V−9
IOVCC
Shutdown Supply Current
VCC
V+
V−
ANALOG MUX
MUX DC Output Impedance
MUX Leakage Current
MUX Output Voltage Range
MUX Continuous Current10
Junction Temperature Sense Slope
Junction Temperature Accuracy
AC PERFORMANCE
Settling Time
0 V to 5 V Range, ±5 V Step
0 V to 10 V Range or ±5 V Range, ±10 V
Step
±10 V Range, ±20 V Step
±15 V Range, ±30 V Step
Voltage Output Slew Rate
Capacitive Load Driving
Glitch Impulse11
DAC to DAC Crosstalk12
Output Noise Spectral Density
DIGITAL INPUT/OUTPUT (I/O)
Digital Output High Voltage
Digital Output Low Voltage
Digital High-Z Output Leakage
analog.com
Symbol
Test Conditions/Comments
V2+
V−
IOVCC
IVCC
IS
IIOVCC
Min
Typ
VCC – 0.3
–21
1.71
VCC = 5 V; 0 V to 5 V range
VCC = 5 V; 0 V to 10 V range
VCC = 5 V; ±5 V range
VCC = 5 V; ±10 V range
VCC = 5 V; ±15 V range
Vx+/V− = ±15 V; 0 V to 5 V range
Vx+/V− = ±15 V; 0 V to 10 V range
Vx+/V− = ±15 V; ±5 V range
Vx+/V− = ±15 V; ±10 V range
Vx+/V− = ±15 V; ±15 V range
IOVCC = 5 V, digital inputs at IOVCC or GND
21.9
22.3
25.6
29.6
33.6
6.4
6.4
8.3
10.8
13
0.05
VCC = 5 V
V+/V− = ±15 V
V+/V− = ±15 V
20
30
−30
Max
Unit
V1+ + 0.3
0
VCC + 0.3
V
V
V
mA
mA
mA
mA
mA
mA
mA
mA
mA
mA
μA
37.0
15
1
μA
μA
μA
3.5
7.95
±5
kΩ
μA
V
mA
mV/°C
°C
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