AD8610/AD8620

The slew rate of the AD8610/AD8620 is double that of the

Input Overvoltage Protection

OPA627 when configured in a unity gain of +1 (see Figure 53

and Figure 54).

strate through the negative supply (V–) or the positive supply

(V+), respectively, to the input pins and can destroy the device.

G= +1

If the input source can deliver larger currents than the maximum

forward current of the diode (>5 mA), a series resistor can be

added to protect the inputs. With its very low input bias and

offset current, a large series resistor can be placed in front of

the AD8610/AD8620 inputs to limit current to below damaging

SR = 85V/µs

levels. Series resistance of 10 kΩ generates less than 25 μV of offset.

This 10 kΩ allows input voltages more than 5 V beyond either

power supply. Thermal noise generated by the resistor adds

7.5 nV/√Hz to the noise of the AD8610/AD8620. For the AD8610/

AD8620, differential voltages equal to the supply voltage do not

cause any problem (see Figure 55). In this context, please note that

TIME (400ns/DIV)

the high breakdown voltage of the input FETs eliminates the need

Figure 53. +Slew Rate of AD8610/AD8620 in Unity Gain of +1

to include clamp diodes between the inputs of the amplifier, a prac-

tice that is mandatory on many precision op amps. Unfortunately,

G= +1

clamp diodes greatly interfere with many application circuits

such as precision rectifiers and comparators. The AD8610/

AD8620 are free from these limitations.

+13V

3

7

6

2

–13V

4

AD8610

V1

14V

SR = 23V/µs

0

Figure 56. Unity Gain Follower

No Phase Reversal

Many amplifiers misbehave when one or both of the inputs are

TIME (400ns/DIV)

Figure 54. +Slew Rate of OPA627 in Unity Gain of +1

forced beyond the input common-mode voltage range. Phase

reversal is typified by the transfer function of the amplifier, effect-

The slew rate of an amplifier determines the maximum frequency

tively reversing its transfer polarity. In some cases, this can cause

at which it can respond to a large signal input. This frequency

lockup and even equipment damage in servo systems, and can

(known as full-power bandwidth or FPBW) can be calculated

cause permanent damage or no recoverable parameter shifts to

for a given distortion (for example, 1%) from the equation:

the amplifier itself. Many amplifiers feature compensation cir-

SR

cuitry to combat these effects, but some are only effective for

FPBW =

the inverting input. The AD8610/AD8620 are designed to prevent

phase reversal when one or both inputs are forced beyond their

input common-mode voltage range.

0V

0V

TIME (400ns/DIV)

Figure 55. AD8610 FPBW

TIME (400µs/DIV)

Figure 57. No Phase Reversal

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