Datasheet

MAX5150/MAX5151
Bipolar Output
The MAX5150/MAX5151 can be configured for a bipo-
lar output, as shown in Figure 11. The output voltage is
given by the equation (OS_ = AGND):
V
OUT
= V
REF
[((2 x NB) / 8192) - 1]
where NB represents the numeric value of the DAC’s
binary input code. Table 3 shows digital codes and the
corresponding output voltage for Figure 11’s circuit.
Using an AC Reference
In applications where the reference has an AC signal
component, the MAX5150/MAX5151 have multiplying
capabilities within the reference input voltage range
specifications. Figure 12 shows a technique for apply-
ing a sinusoidal input to REF_, where the AC signal is
offset before being applied to REF.
Harmonic Distortion and Noise
The total harmonic distortion plus noise (THD+N) is typ-
ically less than -78dB at full scale with a 1Vp-p input
swing at 5kHz. The typical -3dB frequency is 300kHz
for both devices, as shown in the Typical Operating
Characteristics.
Digital Calibration and
Threshold Selection
Figure 13 shows the MAX5150/MAX5151 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 stores this
“high” calibration value. Repeat the process with a
dim light (off) to obtain the dark current calibration.
Low-Power, Dual, 13-Bit Voltage-Output DACs
with Serial Interface
14 ______________________________________________________________________________________
Table 3. Bipolar Code Table
ANALOG OUTPUT
11111 1111 1111
10000 0000 0001
DAC CONTENTS
MSB LSB
10000 0000 0000 0V
01111 1111 1111
00000 0000 0000
00000 0000 0001
+V
4095
4096
REF






+V
1
4096
REF






-V
1
4096
REF






-V
4095
4096
REF






-V
4096
4096
- V
REF REF






=
AGNDDGND
R
R
TOLERANCES: 10kΩ ± 0.1%
MAX5150
MAX5151
DAC _
REF_
OS_
OUT_
10k 10k
10k
10k
V-
V+
V
DD
V
OUT
+5V/+3V
Figure 11. Bipolar Output Circuit
DAC_
OUT
MAX5150
MAX5151
10k
26k
OS_
REF
R
R
V
DD
GNDAGND
+5V/
+3V
AC
REFERENCE
INPUT
500mVp-p
MAX495
+5V/+3V
Figure 12. AC Reference Input Circuit
AGND
DIN
µP
DGND
MAX5150
MAX5151
DAC _
REF_
OS_
OUT_
R
R
V-
V+
PHOTODIODE
V+
V
DD
V
OUT
R
PULLDOWN
+5V/+3V
Figure 13. Digital Calibration