Rainbow Electronics MAX5151 - Manual (Page 14)

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
1 1 1 1 1 1 1 1 1 1 1 1 1
1 0 0 0 0 0 0 0 0 0 0 0 1
DAC CONTENTS
MSB LSB
1 0 0 0 0 0 0 0 0 0 0 0 0 0V
0 1 1 1 1 1 1 1 1 1 1 1 1
0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 1
+V
4095
4096
REF

 

+V
1
4096
REF

 

-V
1
4096
REF

 

-V
4095
4096
REF

 

-V
4096
4096
- V
REF REF

 

=
AGND DGND
R
R
TOLERANCES: 10k Ω ± 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
GND AGND
+5V/
+3V
AC
REFERENCE
INPUT
500mVp-p
MAX495
+5V/+3V
Figure 12. AC Reference Input Circuit
AGND
DIN
µ P
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