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).
02730-053
VOLTAGE (5V/DIV)
TIME (400ns/DIV)
V
S
= ±13V
R
L
= 2kΩ
G= +1
SR = 85V/µs
Figure 53. +Slew Rate of AD8610/AD8620 in Unity Gain of +1
02730-054
VOLTAGE (5V/DIV)
TIME (400ns/DIV)
V
S
= ±13V
R
L
= 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
V
SR
FPBW
×π
=
2
02730-055
VOLTAGE (10V/DIV)
TIME (400ns/DIV)
CH
1
= 20.8V p-p
CH
2
= 19.4V p-p
0V
0V
Figure 55. AD8610 FPBW
Input Overvoltage Protection
When the input of an amplifier is driven below V
EE
or above V
CC
by more than one V
BE
, 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 k generates less than 25 V of offset.
This 10 k 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.
V1
–13V
3
2
7
4
+13
14V
0
6
AD8610
02730-056
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.
02730-057
VOLTAGE (5V/DIV)
TIME (400µs/DIV)
V
OUT
V
IN
Figure 57. No Phase Reversal
