Datasheet

25
LTC1290
1290fe
U
S
A
O
PP
L
IC
AT
I
WU
U
I FOR ATIO
How the various power supplies to the LTC1290 are
applied can also lead to overvoltage conditions. For single
supply operation (i.e., unipolar mode), if V
CC
and REF
+
are
not tied together, then V
CC
should be turned on first, then
REF
+
. If this sequence cannot be met, connecting a diode
from REF
+
to V
CC
is recommended (see Figure 21).
For dual supplies (bipolar mode) placing two Schottky
diodes from V
CC
and V
–
to ground (Figure 23) will prevent
power supply reversal from occurring when an input
source is applied to the analog MUX before power is
applied to the device. Power supply reversal occurs, for
example, if the input is pulled below V
–
then V
CC
will pull
a diode drop below ground which could cause the device
not to power up properly. Likewise, if the input is pulled
above V
CC
then V
–
will be pulled a diode drop above
ground. If no inputs are present on the MUX, the Schottky
diodes are not required if V
–
is applied first, then V
CC
.
Because a unique input protection structure is used on the
digital input pins, the signal levels on these pins can
exceed the device V
CC
without damaging the device.
5V
1290 F21
REF
+
V
CC
LTC1290
22µF
1N4148
V
REF
14
20
5V
1290 F22
DGND
V
–
AGND
V
CC
LTC1290
–5V
0.1µF
22µF
1N5817
1N5817
Figure 21 Figure 22. Power Supply Reversal
Figure 20. Overvoltage Protection for MUX
5V
1290 F20
DGND
V
–
AGND
V
CC
1k
LTC1290
CH0
V
IN
–5V
0.1µF
22µF