Datasheet

TLC7225C, TLC7225I
QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS
SLAS109B – OCTOBER 1996 – REVISED FEBRUARY 2001
11
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
ground management and layout
The TLC7225 contains four reference inputs that can be driven from ac sources (see multiplying DAC using ac
input to the REF terminals section) so careful layout and grounding is important to minimize analog crosstalk
between the four channels. The dynamic performance of the four DACs depends upon the optimum choice of
board layout. Figure 6 shows the relationship between input frequency and channel-to-channel isolation.
Figure 7 shows a printed circuit board layout that minimizes crosstalk and feedthrough. The four input signals
are screened by AGND. V
ref
was limited between 2 V and 3.24 V to avoid slew-rate limiting effects from the
output amplifier during measurements.
–80
–70
–60
–50
–40
–30
20 k 50 k 100 k 200 k 500 k 1 M
f
I
– Input Frequency – Hz
Isolation – dB
T
A
= 25°C
V
DD
= 15 V
V
SS
= –5 V
V
ref
= 1.24 V
PP
–20
10 k
Figure 6. Channel-to-Channel Isolation
MSB LSB
Terminal 1
System GND
OUTB
OUTA
V
SS
REFB
REFA
AGND
DGND
OUTC
OUTD
V
DD
REFC
REFD
Figure 7. Suggested PCB Layout (Top View)