AD813 datasheet(15/19 Pages) AD

15 / 19 page

AD813

REV. B

–15–

Overload Recovery

There are three important overload conditions to consider.

They are due to: input common-mode voltage overdrive, out-

put voltage overdrive, and input current overdrive. When the

amplifier is configured for low closed-loop gains, and the input

common-mode voltage range is exceeded, the recovery time will

be very fast, typically under 30 ns. When configured for a

higher gain, and overloaded at the output, the recovery time will

also be short. For example, in a gain of +10, with 6 dB of

input overdrive, the recovery time of the AD813 is about 25 ns

(see Figure 45).

50ns

100

Figure 45. 6 dB Overload Recovery, G = +10,

(RL = 500 Ω, RF = 357 Ω, VS = ±5 V)

In the case of high gains with very high levels of input overdrive,

a longer recovery time will occur. For example, if the input

common-mode voltage range is exceeded in the gain of +10, the

recovery time will be on the order of 100 ns. This is primarily

due to current overloading of the input stage.

As noted in the warning under Maximum Power Dissipation, a

high level of input overdrive in a high noninverting gain circuit

can result in a large current flow in the input stage. Though this

current is internally limited to about 40 mA, its effect on the

total power dissipation may be significant.

1000

100

FREQUENCY – MHz

–3

RS = 50

RS = 30

RS = 0

VS = 5V

G = +2

RF = 750

RL = 1k

CL = 10pF

Figure 42. Response to a Small Load Capacitor at

VS = ±5 V

1000

100

FREQUENCY – MHz

–3

CL = 150pF, RS = 30

VS = 15V

G = +2

RF = 750

RL = 1k

CL = 510pF, RS = 15

Figure 43. Response to a Large Load Capacitor at

VS = ±15 V

100n s

100

Figure 44. Circuit of Figure 38 Driving a 510 pF Load

Capacitor, VS = ±15 V (RL = 1 kΩ, RF = RG = 750 Ω,

RS =15

Ω)

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