AD8682 datasheet(21/25 Pages) AD

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Data Sheet

ADA4096-2/ADA4096-4

Rev. G | Page 21 of 25

INPUT OVERVOLTAGE PROTECTION

The ADA4096-2 family inputs are protected from input voltage

excursions up to 32 V outside each rail. This feature is of

particular importance in applications with power supply

sequencing issues that could cause the signal source to be active

before the power supplies.

Figure 55 shows the input current limiting capability of the

ADA4096-2 (green curves) compared to using a 5 kΩ series

resistor (red curves).

–48 –40 –32 –24 –16

–8

–7

–6

–5

–4

–3

–2

–1

VIN (V)

LOW RDSON SERIES FET

5kΩ SERIES RESISTOR

Figure 55. Input Current Limiting Capability

Figure 55 was generated with the ADA4096-2 in a buffer

configuration with the supplies connected to GND (or ±15 V)

and the positive input swept until it exceeds the supplies by

32 V. In general, input current is limited to 1 mA during

positive overvoltage conditions and 200 µA during negative

undervoltage conditions. For example, at an overvoltage of 20 V,

the ADA4096-2 input current is limited to 1 mA, providing a

current-limit equivalent to a series 20 kΩ resistor. Figure 55 also

shows that the current limiting circuitry is active whether the

amplifier is powered or not.

Note that Figure 55 represents input protection under abnormal

conditions only. The correct amplifier operation input voltage

range (IVR) is specified in Table 2 to Table 4.

COMPARATOR OPERATION

Although op amps are quite different from comparators,

occasionally an unused section of a dual or a quad op amp may

be pressed into service as a comparator; however, this is not

recommended for any rail-to-rail output op amps. For rail-to-

rail output op amps, the output stage is generally a ratioed

current mirror with bipolar or metal-oxide semiconductor

field-effect (MOSFET) transistors. With the device operating in

open loop, the second stage increases the current drive to the

ratioed mirror to close the loop, but it cannot, which results in

an increase in supply current. With the op amp configured as a

comparator, the supply current can be significantly higher (see

Figure 56).

500

400

300

200

100

SUPPLY VOLTAGE (V)

VOUT = HIGH

VOUT = LOW

BUFFER

Figure 56. Comparator Supply Current

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