22
LTC1292/LTC1297
12927fb
U
S
A
O
PP
L
IC
AT
I
WU
U
I FOR ATIO
LSB
(B0)
LSB-FIRST DATA
(B1)
MSB
(B11)
NULL
BIT
VERTICAL: 5V/DIV
HORIZONTAL: 2µs/DIV
CLK
CS
D
OUT
A “Quick Look” Circuit for the LTC1297
A circuit similar to the one used for the LTC1292 can be
used for the LTC1297(Figure 28). A one shot has been
generated with NAND gates, a resistor and capacitor to
satisfy the setup time t
suCS
. This can be eliminated if a
slower clock is used. When CS goes low the one shot is
triggered. This turns off the clock to the LTC1297 for a
fixed time to meet t
suCS
. Once the clock starts D
OUT
is
shifted out one bit at a time. CS is driven at 1/64 the
clock rate by the 74HC393. The output data from the
D
OUT
pin can be viewed on an oscilloscope that is set to
trigger on the falling edge of CS. See Figure 29.
CS
CLK
D
OUT
NULL
BIT
MSB
(B11)
LSB-FIRST DATA
(B1)
LSB
(B0)
VERTICAL: 5V/DIV
HORIZONTAL: 5µs/DIV
Figure 29. Scope Trace of the LTC1297 “Quick Look”
Circuit Showing A/D Output 101010101010 (AAA
HEX
)
Figure 27. Scope Trace of the LTC1292 “Quick Look”
Circuit Showing A/D Output 101010101010 (AAA
HEX
)
Figure 28. “Quick Look” Circuit for the LTC1297
TO OSCILLOSCOPE
LTC1292/7 F28
0.1µF
V
IN
f/64
5V
340Ω
22µF
TANTALUM
V
CC
CLK
D
OUT
V
REF
CS
+IN
–IN
GND
LTC1297
74HC393
A1
CLR1
1QA
1QB
1QC
1QD
GND
V
CC
A2
CLR2
2QA
2QB
2QC
2QD
+
f
0.02µF
CLOCK IN 1MHz
A “Quick Look” Circuit for the LTC1292
Users can get a quick look at the function and timing of
the LTC1292 by using the “Quick Look” circuit in Figure
26. V
REF
is tied to V
CC
. V
IN
is applied to the +IN input
and the –IN input is tied to the ground plane. CS is driven
at 1/32 the clock rate by the CD4520 and D
OUT
outputs
the data. The output data from the D
OUT
pin can be
viewed on an oscilloscope that is set up to trigger on the
falling edge of CS (Figure 27). Note the LSB data is
partially clocked out before CS goes high.
