LTC1290BCSW datasheet(25/32 Pages) LINER

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LTC1290

1290fe

APPLICATI

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 VCC and REF+ are

not tied together, then VCC should be turned on first, then

REF+. If this sequence cannot be met, connecting a diode

from REF+ to VCC is recommended (see Figure 21).

For dual supplies (bipolar mode) placing two Schottky

diodes from VCC 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 VCC will pull

a diode drop below ground which could cause the device

not to power up properly. Likewise, if the input is pulled

above VCC 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 VCC.

Because a unique input protection structure is used on the

digital input pins, the signal levels on these pins can

exceed the device VCC without damaging the device.

1290 F21

REF+

VCC

LTC1290

µF

1N4148

VREF

1290 F22

DGND

V –

AGND

VCC

LTC1290

–5V

0.1

µF

1N5817

Figure 21

Figure 22. Power Supply Reversal

Figure 20. Overvoltage Protection for MUX

1290 F20

DGND

V–

AGND

VCC

LTC1290

CH0

VIN

–5V

0.1

µF

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