max5235 Maxim Integrated Products, Inc., max5235 Datasheet - Page 13

• Manufacturer Part Number: max5235
• Description: Single-supply 3v/5v, Voltage-output, Dual, Precision 12-bit Dacs
• Manufacturer: Maxim Integrated Products, Inc.

Table 2. Serial Interface Programming Commands
X = Don’t care.
* = S0 must be zero for proper operation.
2.0475V output with a 1.25V reference. Table 4 lists the
unipolar output codes.
The MAX5234/MAX5235 can be configured for a bipo-
lar output, as shown in Figure 8. The output voltage is
given by the equation:
where NB represents the numeric value of the DAC’s
binary input code. Table 5 shows digital codes and the
corresponding output voltage for Figure 8’s circuit.
In applications where the reference has an AC signal
component, the MAX5234/MAX5235 have multiplying
capabilities within the reference input voltage range
specifications. Figure 9 shows a technique for applying
a sinusoidal input to REF_, where the AC signal is offset
before being applied to the reference input.
C2
0
0
0
1
1
1
1
0
0
0
0
0
V
C1
OUT
0
1
1
0
0
1
1
0
0
0
0
0
Single-Supply 3V/5V, Voltage-Output, Dual,
= V
C0
1
0
1
0
1
0
1
0
0
0
0
0
REF
16-BIT SERIAL WORD
______________________________________________________________________________________
[((1.6348 x NB) / 4096) - 1]
P1A P1B X X X X X X X X X X
0 1 1 P1A P1B X X X X X X X
1 1 0 P1A X X X X X X X X
1 1 1 P1B X X X X X X X X
X X X X X X X X X X X X
0 0 1 X X X X X X X X X
1 0 1 X X X X X X X X X
Using an AC Reference
12-bit DAC data
12-bit DAC data
12-bit DAC data
12-bit DAC data
12-bit DAC data
D11..............D0
Bipolar Output
S0*
0
0
0
0
0
0
0
0
0
0
0
0
Load input register A; DAC registers are unchanged.
Load input register A; all DAC registers are updated.
Load all DAC registers from the shift register (start up both DACs
with new data, and load the input registers).
Update both DAC registers from their respective input registers
(start up both DACs with data previously stored in the input
registers).
Load input register B; DAC registers are unchanged.
Load input register B; all DAC registers are updated.
Power down both DACs respectively according to bits P1A and
P1B (see Table 3). Internal bias remains active.
Update DAC register A from input register A (start up DAC A with
data previously stored in input register A).
Full power-down. Power down the main bias generator and
power down both DACs respectively according to bits P1A and
P1B (see Table 3).
Update DAC register B from input register B (start up DAC B with
data previously stored in input register B).
Power down DAC A according to bit P1A (see Table 3).
Power down DAC B according to bit P1B (see Table 3).
Figure 10 shows the MAX5234/MAX5235 in a digital
calibration application. With a bright light value applied
to the photodiode (on), the DAC is digitally ramped until
it trips the comparator. The microprocessor (µP) stores
this “high” calibration value. Repeat the process with a
dim light (off) to obtain the dark current calibration. The
µP then programs the DAC to set an output voltage at
the midpoint of the two calibrated values. Applications
include tachometers, motion sensing, automatic read-
ers, and liquid clarity analysis.
Table 3. P1 Shutdown Modes
P1(A/B)
Precision 12-Bit DACs
0
1
Shut down with internal 200kΩ load to GND
Shut down with internal 1kΩ load to GND
FUNCTION
SHUTDOWN MODE
Digital Calibration and
Threshold Selection
13