LTC1292_15 Datasheet, PDF (22/24 Pages) Linear Technology – Single Chip 12-Bit Data Acquisition Systems

LTC1292/LTC1297
APPLICATI S I FOR ATIO
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.
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.
CLK
CS
CLK
D_OUT
NULL
BIT
MSB
LSB
(B11)
(B0)
VERTICAL: 5V/DIV
HORIZONTAL: 2µs/DIV
LSB-FIRST DATA
(B1)
Figure 27. Scope Trace of the LTC1292 “Quick Look”
Circuit Showing A/D Output 101010101010 (AAA_HEX)
22µF
TANTALUM
f/64
f
CS
V_CC
V_IN
+IN
CLK
LTC1297
–IN
D_OUT
GND
V_REF
CS
D_OUT
NULL MSB LSB LSB-FIRST DATA
BIT (B11) (B0)
(B1)
VERTICAL: 5V/DIV
HORIZONTAL: 5µs/DIV
Figure 29. Scope Trace of the LTC1297 “Quick Look”
Circuit Showing A/D Output 101010101010 (AAA_HEX)
A1
V_CC
CLR1
A2
1QA
CLR2
1QB 74HC393 2QA
1QC
2QB
1QD
2QC
GND
2QD
5V
0.1µF
22
TO OSCILLOSCOPE
340Ω
0.02µF
CLOCK IN 1MHz
Figure 28. “Quick Look” Circuit for the LTC1297
LTC1292/7 F28
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