MAX5352/MAX5353
Low-Power, 12-Bit Voltage-Output DACs
with Serial Interface
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_______________Detailed Description
The MAX5352/MAX5353 contain a voltage-output digi-
tal-to-analog converter (DAC) that is easily addressed
using a simple 3-wire serial interface. Each IC includes
a 16-bit shift register, and has a double-buffered input
composed of an input register and a DAC register (see
Functional Diagram
). In addition to the voltage output,
the amplifier’s negative input is available to the user.
The DAC is an inverted R-2R ladder network that con-
verts a digital input (12 data bits plus one sub-bit) into
an equivalent analog output voltage in proportion to the
applied reference voltage. Figure 1 shows a simplified
circuit diagram of the DAC.
Reference Inputs
The reference input accepts positive DC and AC sig-
nals. The voltage at the reference input sets the full-
scale output voltage for the DAC. The reference input
voltage range is 0V to (V
DD
- 1.4V). The output voltage
(V
OUT
) is represented by a digitally programmable volt-
age source, as expressed in the following equation:
V
OUT
= (V
REF
x NB / 4096) x Gain
where NB is the numeric value of the DAC’s binary
input code (0 to 4095), V
REF
is the reference voltage,
and Gain is the externally set voltage gain.
The impedance at the reference input is code depen-
dent, ranging from a low value of 14kΩ when the DAC
has an input code of 1554 hex, to a high value exceed-
ing several giga ohms (leakage currents) with an input
code of 0000 hex. Because the input impedance at the
reference pin is code dependent, load regulation of the
reference source is important.
In shutdown mode, the MAX5352/MAX5353’s REF input
enters a high-impedance state with a typical input leak-
age current of 0.001µA.
The reference input capacitance is also code depen-
dent and typically ranges from 15pF (with an input
code of all 0s) to 50pF (at full scale).
The MAX873 +2.5V reference is recommended for the
MAX5352.
Output Amplifier
The MAX5352/MAX5353’s DAC output is internally
buffered by a precision amplifier with a typical slew rate
of 0.6V/µs. Access to the output amplifier’s inverting
input provides the user greater flexibility in output gain
setting/signal conditioning (see the
Applications
Information
section).
With a full-scale transition at the MAX5352/MAX5353
output, the typical settling time to ±1/2LSB is 14µs
when loaded with 5kΩ in parallel with 100pF (loads less
than 2kΩ degrade performance).
The amplifier’s output dynamic responses and settling
performances are shown in the
Typical Operating
Characteristics
.
Shutdown Mode
The MAX5352/MAX5353 feature a software-program-
mable shutdown that reduces supply current to a typical
value of 4µA. Writing 111X XXXX XXXX XXXX as the input-
control word puts the device in shutdown mode (Table 1).
In shutdown mode, the amplifier’s output and the refer-
ence input enter a high-impedance state. The serial
interface remains active. Data in the input registers is
retained in shutdown, allowing the MAX5352/MAX5353
