Datasheet

TLC7225C, TLC7225I
QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS
SLAS109B – OCTOBER 1996 – REVISED FEBRUARY 2001
14
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
AGND bias for positive output offset
The TLC7225 AGND terminal can be biased above or below the system ground terminal, DGND, to provide an
offset-zero analog-output voltage level. Figure 10 shows a circuit configuration to achieve this for channel A of
the TLC7225. The output voltage, V
O
at OUTA, can be expressed as:
V
O
V
bias
D
A
V
I
where D
A
is a fractional representation of the digital input word (0 ≤ D ≤ 255/256).
_
+
DAC A
AGND
DGND
TLC7225
†
V
ref
V
O(OUTA)
5 22
2
73
V
DD
6
V
SS
V
I
V
bias
†
Digital inputs omitted for clarity.
Figure 10. AGND Bias Circuit
Increasing AGND above system ground 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 TLC7225. Supply voltages V
DD
and V
SS
for the TLC7225 should be referenced
to DGND.