_______________Detailed Description
The MAX5156/MAX5157 dual, 12-bit, voltage-output
DACs are easily configured with a 3-wire serial inter-
face. These devices include a 16-bit data-in/data-out
shift register, and each DAC has a double-buffered
input comprised of an input register and a DAC register
(see
Functional Diagram
). Both DACs use an inverted
R-2R ladder network that produces a weighted voltage
proportional to the input voltage value. Each DAC has
its own reference input to facilitate independent full-
scale values. Figure 1 depicts a simplified circuit dia-
gram of one of the two DACs.
Reference Inputs
The reference inputs accept both AC and DC values
with a voltage range extending from 0V to (V
DD
- 1.4V).
Determine the output voltage using the following equa-
tion:
V
OUT
= V
REF
x NB / 4096
where NB is the numeric value of the DAC’s binary input
code (0 to 4095) and V
REF
is the reference voltage.
The reference input impedance ranges from 14kΩ (1554
hex) to several giga ohms (with an input code of 0000
hex). This reference input capacitance is code depen-
dent and typically ranges from 15pF with an input code
of all zeros to 50pF with a full-scale input code.
Output Amplifier
The output amplifier’s inverting input is available to the
user, allowing force and sense capability for remote
sensing and specific gain configurations. The inverting
input can be connected to the output to provide a unity-
gain buffered output. The output amplifiers have a typi-
cal slew rate of 0.75V/µs and settle to 1/2LSB within
15µs, with a load of 10kΩ in parallel to 100pF. Loads
less than 2kΩ degrade performance.
MAX5156/MAX5157
Low-Power, Dual, 12-Bit Voltage-Output DACs
with Configurable Outputs
_______________________________________________________________________________________ 9
______________________________________________________________Pin Description
PIN
Analog GroundAGND1
FUNCTIONNAME
DAC A Output VoltageOUTA2
Reference for DAC AREFA4
DAC A Output Amplifier Feedback Input. Inverting input of the output amplifier.FBA3
Chip-Select Input
CS
6
Serial Clock Input SCLK8
Serial Data InputDIN7
Active-Low Clear Input. Resets all registers to zero. DAC outputs go to 0V.
CL
5
Serial Data OutputDOUT10
Power-Down Lockout. The device cannot be powered down when PDL is low.PDL
12
User-Programmable OutputUPO11
DAC B Output Amplifier Feedback Input. Inverting input of the output amplifier.FBB14
Positive Power SupplyV
DD
16
DAC B Output VoltageOUTB15
Reference Input for DAC BREFB13
Digital GroundDGND9
