OPA2991IDDFR datasheet(32/77 Pages) TI

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7.3.8 Overload Recovery

Overload recovery is defined as the time required for the op amp output to recover from a saturated state to a

linear state. The output devices of the op amp enter a saturation region when the output voltage exceeds the

rated operating voltage, either due to the high input voltage or the high gain. After the device enters the

saturation region, the charge carriers in the output devices require time to return back to the linear state. After

the charge carriers return back to the linear state, the device begins to slew at the specified slew rate. Thus, the

propagation delay in case of an overload condition is the sum of the overload recovery time and the slew time.

The overload recovery time for the OPAx991 is approximately 500 ns.

7.3.9 Typical Specifications and Distributions

Designers often have questions about a typical specification of an amplifier in order to design a more robust

circuit. Due to natural variation in process technology and manufacturing procedures, every specification of an

amplifier will exhibit some amount of deviation from the ideal value, like an amplifier's input offset voltage. These

deviations often follow Gaussian ("bell curve"), or normal distributions, and circuit designers can leverage this

information to guardband their system, even when there is not a minimum or maximum specification in the

Section 6.7 table.

0.00002%

-1

-21

-31

-41

-51

-61

+21

+31

+41

+51

+61

34.13% 13.59%

34.13%

13.59%

2.145%

2.145% 0.13185%

0.13185%

0.00312%

Figure 7-11. Ideal Gaussian Distribution

Figure 7-11 shows an example distribution, where µ, or mu, is the mean of the distribution, and where σ, or

sigma, is the standard deviation of a system. For a specification that exhibits this kind of distribution,

approximately two-thirds (68.26%) of all units can be expected to have a value within one standard deviation, or

one sigma, of the mean (from µ–σ to µ+σ).

Depending on the specification, values listed in the typical column of the Section 6.7 table are represented in

different ways. As a general rule of thumb, if a specification naturally has a nonzero mean (for example, like gain

bandwidth), then the typical value is equal to the mean (µ). However, if a specification naturally has a mean near

zero (like input offset voltage), then the typical value is equal to the mean plus one standard deviation (µ + σ) in

order to most accurately represent the typical value.

You can use this chart to calculate approximate probability of a specification in a unit; for example, for OPAx991,

the typical input voltage offset is 125 µV, so 68.2% of all OPAx991 devices are expected to have an offset from –

OPA991, OPA2991, OPA4991

SBOS969D – OCTOBER 2019 – REVISED JULY 2020

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