Datasheet

AD8610/AD8620
Rev. F | Page 15 of 24
Slew Rate (Unity Gain Inverting vs. Noninverting)
Amplifiers generally have a faster slew rate in an inverting unity
gain configuration due to the absence of the differential input
capacitance. Figure 49 through Figure 52 show the performance
of the AD8610/AD8620 configured in a unity gain of –1 compared
to the OPA627. The AD8610/AD8620 slew rate is more symme-
trical, and both the positive and negative transitions are much
cleaner than in the OPA627.
02730-049
VOLTAGE (5V/DIV)
TIME (400ns/DIV)
V
S
= ±13V
R
L
= 2kΩ
G= –1
SR = 54V/µs
Figure 49. +Slew Rate of AD8610/AD8620 in Unity Gain of –1
02730-050
VOLTAGE (5V/DIV)
TIME (400ns/DIV)
V
S
= ±13V
R
L
= 2kΩ
G= –1
SR = 42.1V/µs
Figure 50. +Slew Rate of OPA627 in Unity Gain of –1
02730-051
VOLTAGE (5V/DIV)
TIME (400ns/DIV)
V
S
= ±13V
R
L
= 2kΩ
G= –1
SR = 54V/µs
Figure 51. –Slew Rate of AD8610/AD8620 in Unity Gain of –1
02730-052
VOLTAGE (5V/DIV)
TIME (400ns/DIV)
V
S
= ±13V
R
L
= 2kΩ
G= –1
SR = 56V/µs
Figure 52. –Slew Rate of OPA627 in Unity Gain of –1
The AD8610/AD8620 have a very fast slew rate of 60 V/s even
when configured in a noninverting gain of +1. This is the toughest
condition to impose on any amplifier because the input common-
mode capacitance of the amplifier generally makes its SR appear
worse. The slew rate of an amplifier varies according to the voltage
difference between its two inputs. To observe the maximum SR,
a voltage difference of about 2 V between the inputs must be
ensured. This is required for virtually any JFET op amp so that
one side of the op amp input circuit is completely off, thus maxi-
mizing the current available to charge and discharge the internal
compensation capacitance. Lower differential drive voltages
produce lower slew rate readings. A JFET input op amp with a
slew rate of 60 V/s at unity gain with V
IN
= 10 V may slew at
20 V/s if it is operated at a gain of +100 with V
IN
= 100 mV.