LTC1860/LTC1861
13
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For more information www.linear.com/LTC1860
applicaTions inForMaTion
Reference Input
The reference input of the LTC1861 SO-8 package is
internally tied to V
CC
. The span of the A/D converter is
therefore equal to V
CC
. The voltage on the reference input
of the LTC1861 MSOP package defines the span of the
A/D converter. The LTC1861 MSOP package can operate
with reference voltages from 1V to V
CC
.
GENERAL ANALOG CONSIDERATIONS
Grounding
The LTC1860/LTC1861 should be used with an analog
ground plane and single point grounding techniques. Do not
use wire wrapping techniques to breadboard and evaluate
the device. To achieve the optimum performance, use a
printed circuit board. The ground pins (AGND and DGND
for the LTC1861 MSOP package and GND for the LTC1860
and LTC1861 SO-8 package) should be tied directly to the
analog ground plane with minimum lead length.
Bypassing
For good performance, the V
CC
and V
REF
pins must be free
of noise and ripple. Any changes in the V
CC
/V
REF
voltage
with respect to ground during the conversion cycle can
induce errors or noise in the output code. Bypass the V
CC
and V
REF
pins directly to the analog ground plane with a
minimum of 1µF tantalum. Keep the bypass capacitor
leads as short as possible.
Analog Inputs
Because of the capacitive redistribution A/D conversion
techniques used, the analog inputs of the LTC1860/
LTC1861 have capacitive switching input current spikes.
These current spikes settle quickly and do not cause a
problem if source resistances are less than 200Ω or high
speed op amps are used (e.g., the LT
®
1211, LT1469,
LT1807, LT1810, LT1630, LT1226 or LT1215). But if
large source resistances are used, or if slow settling op
amps drive the inputs, take care to ensure the transients
caused by the current spikes settle completely before the
conversion begins.
