Data Sheet

AD8628/AD8629/AD8630

FUNCTIONAL DESCRIPTION

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Rev. M | 16 of 21

voltage exceeds the supply voltage, these ESD diodes can become

forward-biased. Without current limiting, excessive amounts of cur-

rent could flow through these diodes, causing permanent damage

to the device. If inputs are subject to overvoltage, appropriate series

resistors should be inserted to limit the diode current to less than 5

mA maximum.

OUTPUT PHASE REVERSAL

Output phase reversal occurs in some amplifiers when the input

common-mode voltage range is exceeded. As common-mode volt-

age is moved outside the common-mode range, the outputs of

these amplifiers can suddenly jump in the opposite direction to the

supply rail. This is the result of the differential input pair shutting

down, causing a radical shifting of internal voltages that results in

the erratic output behavior.

The AD8628/AD8629/AD8630 amplifiers have been carefully de-

signed to prevent any output phase reversal, provided that both

inputs are maintained within the supply voltages. If one or both

inputs could exceed either supply voltage, a resistor should be

placed in series with the input to limit the current to less than 5 mA.

This ensures that the output does not reverse its phase.

OVERLOAD RECOVERY TIME

Many auto-zero amplifiers are plagued by a long overload recovery

time, often in ms, due to the complicated settling behavior of the

internal nulling loops after saturation of the outputs. The AD8628/

AD8629/AD8630 have been designed so that internal settling oc-

curs within two clock cycles after output saturation occurs. This

results in a much shorter recovery time, less than 10 µs, when

compared to other auto-zero amplifiers. The wide bandwidth of the

AD8628/AD8629/AD8630 enhances performance when the parts

are used to drive loads that inject transients into the outputs. This is

a common situation when an amplifier is used to drive the input of

switched capacitor ADCs.

Figure 56. Positive Input Overload Recovery for the AD8628

Figure 57. Positive Input Overload Recovery for Competitor A

Figure 58. Positive Input Overload Recovery for Competitor B

Figure 59. Negative Input Overload Recovery for the AD8628