TLC7226C_15 Datasheet, PDF (7/24 Pages) Texas Instruments – QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS

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TLC7226C, TLC7226I, TLC7226M
QUADRUPLE 8ĆBIT DIGITALĆTOĆANALOG CONVERTERS
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SLAS060F − JANUARY 1995 − REVISED APRIL 2009
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^‡
VDD
18
_
AGND
DAC A
+
5
OUT
2
Output range
(5 V to − 5 V)
3
VSS
6
DGND
−5 V
‡ _{Digital inputs omitted for clarity.}
Figure 4. AGND Bias for Direct Bipolar Operation
Table 1. Bipolar (Offset Binary) Code
DAC LATCH CONTENTS
MSB LSB
1111 1111
1000 0001
1000 0000
0111 1111
0000 0001
0000 0000
ANALOG OUTPUT
ǒ Ǔ ) Vref
127
128
ǒ Ǔ ) Vref
1
128
0V
ǒ Ǔ * Vref
1
128
ǒ Ǔ * Vref
127
128
ǒ Ǔ –Vref
128
128
+ * Vref
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:
VO + VBIAS ) DA ^ǒVI^Ǔ
(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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