Datasheet

LTC1272
18
1272fc
For more information www.linear.com/1272
APPLICATIONS INFORMATION
Compatibility with the AD7572
Figure 21 shows the simple, single 5V configuration
recommended for new designs with the LTC1272. If an
AD7572 replacement or upgrade is desired, the LTC1272
can be plugged into an AD7572 socket with minor modi-
fications. It can be used as a replacement or to upgrade
with sample-and-hold, single supply operation and reduced
power consumption.
The LTC1272, while consuming less power overall than the
AD7572, draws more current from the 5V supply (it draws
no power from the –15V supply). Also, a 1µs minimum
time between conversions must be provided to allow the
sample-and-hold to reacquire the analog input. Figure 22
shows that if the clock is synchronous with CS and RD,
it is only necessary to short out the 10Ω series resistor
and reverse the polarity of the 10µF bypass capacitor on
the V
REF
pin. The –15V supply is not required and can be
removed, or, because there is no internal connection to
pin 23, it can remain unmodified. The clock can be con-
sidered synchronous with CS and RD in cases where the
LTC1272 CLK IN signal is derived from the same clock as
the microprocessor reading the LTC1272.
Figure 21. Single 5V Supply, 3µs, 12-Bit Sampling ADC
10µF
IN
REF
D11 (MSB)
D10
D9
D8
D7
CLK IN
CLK OUT
HBEN
RD
CS
BUSY
NC
V
LTC1272
D6
D5
D4
DGND
D3/11
D2/10
D1/9
D0/8
A
V
AGND
DD
µP
CONTROL
LINES
0.1µF*
5V
8 OR 12-BIT
PARALLEL
BUS
ANALOG INPUT
(0V TO 5V)
10µF
0.1µF
*
FOR GROUNDING AND BYPASSING HINTS
SEE FIGURE 11 AND APPLICATION HINTS
SECTION
*
LTC1272 • 21
+
+
2.42V
V
OUTPUT
REF