TLC7225C Datasheet, PDF (16/21 Pages) Texas Instruments – QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS

TLC7225C, TLC7225I
QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS
SLAS109B – OCTOBER 1996 – REVISED FEBRUARY 2001
APPLICATION INFORMATION
digital word multiplication
Since each DAC of the TLC7225 has a separate reference input, the output of one DAC can be used as the
reference input for another. Therefore, multiplication of digital words can be performed (with the result given in
analog form). For example, when the output from DAC A is applied to REFB then the output from DAC B, V_OUTB,
can be expressed as given in equation 2:
V_OUTB = (D_A) (D_B) (V_REFA)
(2)
where D_A and D_B are the fractional representations of the digital words in DAC latches A and B respectively.
If D_A = D_B = D then the result is D² (V_REFA)
In this manner, the four DACs can be used on their own or in conjunction with an external summing amplifier
to generate complex waveforms. Figure 13 shows one such application with the output waveform, Y, which is
represented by equation 3:
Y = –(x⁴ + 2x³ + 3x² + 2x + 4) V_I
(3)
where x is the digital code that is applied to all four DAC latches.
15 V
25 kΩ
100 kΩ
VI
REFA
VDD
OUTA
TLC7225^†
50 kΩ
_
33 kΩ
+
Y
REFB
OUTB
REFC
OUTC
50 kΩ
REFD
OUTD
100 kΩ
AGND DGND VSS
† _{Digital inputs omitted for clarity}
Figure 13. Complex-Waveform Generation
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