TLC7226C, TLC7226I, TLC7226M
QUADRUPLE 8 BIT DIGITAL TO ANALOG CONVERTERS
SLAS060E – JANUARY 1995 – REVISED JANUARY 2003
PRINCIPLES OF OPERATION
AGND bias for direct bipolar output operation
The TLC7226 can be used in bipolar operation without adding more external operational amplifiers as shown
in Figure 4 by biasing AGND to V
SS
. This configuration provides an excellent method for providing a direct
bipolar output with no additional components. The transfer values are shown in Table 1.
REF (Vref = 5 V)
4
TLC7226
‡
_
2
AGND
5
3
VSS
–5 V
‡ Digital inputs omitted for clarity.
6
DGND
DAC A
+
OUT
Output range
(5 V to –5 V)
18
VDD
Figure 4. AGND Bias for Direct Bipolar Operation
Table 1. Bipolar (Offset Binary) Code
DAC LATCH CONTENTS
MSB
LSB
1111
1000
1000
0111
0000
0000
1111
0001
0000
1111
0001
0000
*
V
*
V
–V
ANALOG OUTPUT
)
V
)
V
127
ref 128
1
ref 128
0V
1
ref 128
127
ref 128
128
+ *
V
ref
ref 128
AGND bias for positive output offset
The TLC7226 AGND terminal can be biased above or below the system ground terminal, DGND, to provide an
offset analog output voltage level. Figure 5 shows a circuit configuration to achieve this for channel A of the
TLC7226. The output voltage, V
O
, at OUTA can be expressed as:
V
O
+
V
BIAS
)
D
A
V
I
(1)
where D
A
is a fractional representation of the digital input word (0
≤
D
≤
255/256).
Increasing AGND above system GND reduces the output range. V
DD
– V
ref
must be at least 4 V to ensure
specified operation. Since the AGND terminal is common to all four DACs, this method biases up the output
voltages of all the DACs in the TLC7226. Supply voltages V
DD
and V
SS
for the TLC7226 should be referenced
to DGND.
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