LTC1292 LINER [Linear Technology], LTC1292 Datasheet - Page 13

• Manufacturer Part Number: LTC1292
• Description: Single Chip 12-Bit Data Acquisition Systems
• Manufacturer: LINER [Linear Technology]

A
use a PC board. The ground pin (Pin 4) should be tied
directly to the ground plane with minimum lead length (a
low profile socket is fine). Figure 7 shows an example of
an ideal LTC1292/LTC1297 ground plane design for a two-
sided board. Of course this much ground plane will not
always be possible, but users should strive to get as close
to this ideal as possible.
Bypassing
For good performance, V
ripple. Any changes in the V
ground during a conversion cycle can induce errors or
noise in the output code. V
below 0.5mV by bypassing the V
analog ground plane with a minimum of 22 F tantalum
capacitor and with leads as short as possible. The lead
from the device to the V
Figure 6. Several LTC1292/LTC1297s Sharing One 2-Wire Serial Interface
PPLICATI
OUTPUT PORT
2
SERIAL DATA
MPU
1
0
Figure 8. Poor V
Ripple Can Cause A/D Errors
O
2
2
2 CHANNELS
LTC1292
LTC1297
U
HORIZONTAL: 10 s/DIV
S
CC
CS
CC
I FOR ATIO
supply also should be kept to a
CC
CC
U
Bypassing. Noise and
noise and ripple can be kept
must be free of noise and
2
CC
2 CHANNELS
LTC1292
LTC1297
voltage with respect to
CC
CS
W
pin directly to the
2
2 CHANNELS
LTC1292
LTC1297
CS
U
2-WIRE SERIAL
INTERFACE TO OTHER
PERIPHERALS OR
LTC1292/LTC1297s
minimum and the V
impedance such as obtained from a voltage regulator
(e.g., LT323A). For high frequency bypassing a 0.1 F
ceramic disk placed in parallel with the 22 F is
recommended. Again the leads should be kept to a
minimum. Figures 8 and 9 show the effects of good and
poor V
Analog Inputs
Because of the capacitive redistribution A/D conversion
techniques used, the analog inputs of the LTC1292/
LTC1297 have capacitive switching input current spikes.
These current spikes settle quickly and do not cause a
problem. If large source resistances are used or if slow
settling op amps drive the inputs, take care to insure that
the transients caused by the current spikes settle completely
before the conversion begins.
LTC1292/7 F06
CC
bypassing.
Figure 9. Good V
Noise and Ripple on V
Figure 7. Example Ground Plane
for the LTC1292/LTC1297
HORIZONTAL: 10 s/DIV
CC
TANTALUM
1
2
3
4
supply should have a low output
LTC1292
LTC1297
LTC1292/LTC1297
CC
22µF
Bypassing Keeps
CC
8
7
6
5
V
Below 1mV
CC
0.1µF
LTC1292/7 F07
CS
V
CC
13