Rainbow Electronics MAX5233 - Manual (Page 15)

Digital Feedthrough
Digital feedthrough is noise generated on the DAC’s
output when any digital input transitions. Proper board
layout and grounding significantly reduce this noise,
but there is always some feedthrough caused by the
DAC itself.
Unipolar Output
Figure 7 shows the MAX5232/MAX5233 configured for
unipolar, rail-to-rail operation. The MAX5233 produces
a 0 to 4.092V output, while the MAX5232 produces 0 to
2.046V output. Table 4 lists the unipolar output codes.
Digital Calibration and
Threshold Selection
Figure 8 shows the MAX5232/MAX5233 in a digital cali-
bration 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.
Sharing a Common DIN Line
Several MAX5232/MAX5233s may share one common
DIN signal line (Figure 9). In this configuration, the data
bus is common to all devices; data is not shifted through
a daisy-chain. The SCLK and DIN lines are shared by all
devices, but each IC needs its own dedicated CS line.
Daisy-Chaining Devices
Any number of MAX5232/MAX5233s can be daisy-
chained by connecting the serial data output (DOUT) of
one device to the digital input (DIN) of the following
device in the chain (Figure 10).
MAX5232/MAX5233
3V/5V, 10-Bit, Serial Voltage-Output Dual DACs
with Internal Reference
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Table 4. Unipolar Code Table
DAC CONTENTS ANALOG OUTPUT (V)
MSB LSB MAX5232 MAX5233
1111 1111 11 (000) 2.046 4.092
1000 0000 01 (000) 1.025 2.050
1000 0000 00 (000) 1.023 2.046
0111 1111 11 (000) 1.021 2.042
0000 0000 01 (000) 0.002 0.004
0000 0000 00 (000) 0 0
DAC_
MAX5232
MAX5233
REF
REF
V DD
AGND DGND
5V/3V
OUT_
OS_
121k Ω
77.25k Ω
1k Ω
Figure 7. Unipolar Output Circuit (Rail-to-Rail)
DAC_
MAX5232
MAX5233
REF
REF
V DD
V OUT
AGND DGND
5V/3V
OUT_
PHOTODIODE
OS_
V+
V+
V-
121k Ω
77.25k Ω
1k Ω
R PULLDOWN
Figure 8. Digital Calibration