Rainbow Electronics MAX5511 - Manual (Page 16)

MAX5510/MAX5511
+1.8V to +5.5V, Ultra-Low-Power, 8-Bit,
Voltage-Output DACs
16 ______________________________________________________________________________________
Unipolar Output
Figure 7 shows the MAX5510 in a unipolar output con-
figuration with unity gain. Table 4 lists the unipolar out-
put codes.
Bipolar Output
The MAX5510 output can be configured for bipolar
operation, as shown in Figure 8. The output voltage is
given by the following equation:
V OUT = V REF x [(N A - 128) / 128]
where NA represents the numeric value of the DAC’s
binary input code. Table 5 shows digital codes (offset
binary) and the corresponding output voltage for the
circuit in Figure 4.
Configurable Output Gain
The MAX5510/MAX5511 have a force-sense output,
which provides a connection directly to the inverting ter-
minal of the output op amp, yielding the most flexibility.
The advantage of the force-sense output is that specific
gains can be set externally for a given application. The
gain error for the MAX5510/MAX5511 is specified in a
unity-gain configuration (op-amp output and inverting ter-
minals connected), and additional gain error results from
external resistor tolerances. Another advantage of the
force-sense DAC is that it allows many useful circuits to
be created with only a few simple external components.
Figure 8. Bipolar Output Circuit
DAC CONTENTS
MSB LSB
ANALOG OUTPUT
1111 1111 0000 +V REF (127/128)
1000 0001 0000 +V REF (1/128)
1000 0000 0000 0V
0111 1111 0000 -V REF (1/128)
0000 0001 0000 -V REF (127/128)
0000 0000 0000 -V REF (128/128) = -V REF
Table 5. Bipolar Code Table (Gain = +1)
REFIN
MAX5510
OUT
V OUT
FB
V+
10kΩ 10kΩ
V-
DAC
DAC
BAND
GAP
TO ADC
OUT
REFOUT
MAX5511
TO ADC
TO ADC
FB
WE
SENSOR
CE
I
F R F
C
L
REF
Figure 6. Self-Biased Two-Electrode Potentiostat Application
N A IS THE DAC INPUT CODE
(0 TO 255 DECIMAL).
REFIN
MAX5510
OUT
FB
V
OUT
=
V REFIN × N A
256
DAC
Figure 7. Unipolar Output Circuit
DAC CONTENTS
MSB LSB
ANALOG OUTPUT
1111 1111 0000 +V REF (255/256)
1000 0001 0000 +V REF (129/256)
1000 0000 0000 +V REF (128/256) = +V REF /2
0111 1111 0000 +V REF (127/256)
0000 0001 0000 +V REF (1/256)
0000 0000 0000 0V
Table 4. Unipolar Code Table (Gain = +1)