Datasheet

TLC7225C, TLC7225I
QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS
SLAS109B – OCTOBER 1996 – REVISED FEBRUARY 2001
16
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
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 D
2
(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 = –(x
4
+ 2x
3
+ 3x
2
+ 2x + 4) V
I
(3)
where x is the digital code that is applied to all four DAC latches.
_
+
REFA
REFB
REFC
REFD
OUTA
OUTB
OUTC
OUTD
AGND DGND V
SS
15 V
Y
TLC7225
†
V
I
†
Digital inputs omitted for clarity
100 kΩ
50 kΩ
33 kΩ
50 kΩ
25 kΩ 100 kΩ
V
DD
Figure 13. Complex-Waveform Generation