AD8610 datasheet(16/24 Pages) AD

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AD8610/AD8620

Rev. F | Page 16 of 24

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

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

and Figure 54).

TIME (400ns/DIV)

VS = ±13V

RL = 2kΩ

G= +1

SR = 85V/µs

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

TIME (400ns/DIV)

VS = ±13V

RL = 2kΩ

G= +1

SR = 23V/µs

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

The slew rate of an amplifier determines the maximum frequency

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

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

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

()

PEAK

FPBW

TIME (400ns/DIV)

CH1 = 20.8V p-p

CH2 = 19.4V p-p

Figure 55. AD8610 FPBW

Input Overvoltage Protection

When the input of an amplifier is driven below VEE or above VCC

by more than one VBE, large currents flow from the substrate

through the negative supply (V–) or the positive supply (V+),

respectively, to the input pins and can destroy the device. 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

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 problems (see Figure 55). In this context, note that the

high breakdown voltage of the input FETs eliminates the need to

include clamp diodes between the inputs of the amplifier, a practice

that is mandatory on many precision op amps. Unfortunately,

clamp diodes greatly interfere with many application circuits,

such as precision rectifiers and comparators. The AD8610/

AD8620 are free from these limitations.

–13V

+13V

14V

AD8610

Figure 56. Unity Gain Follower

No Phase Reversal

Many amplifiers misbehave when one or both of the inputs are

forced beyond the input common-mode voltage range. Phase

reversal is typified by the transfer function of the amplifier,

effectively reversing its transfer polarity. In some cases, this can

cause lockup and even equipment damage in servo systems and

can cause permanent damage or no recoverable parameter shifts

to the amplifier itself. Many amplifiers feature compensation

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

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.

TIME (400µs/DIV)

VOUT

VIN

Figure 57. No Phase Reversal

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