Datasheet

Data Sheet ADA4522-1/ADA4522-2/ADA4522-4
Rev. F | Page 23 of 33
SINGLE-SUPPLY AND RAIL-TO-RAIL OUTPUT
The ADA4522-1/ADA4522-2/ADA4522-4 are single-supply
amplifiers, where their input voltage range includes the lower
supply rail. This feature is ideal for applications where the input
common-mode voltage is at the lower supply rail, for example,
ground sensing. Conversely, the amplifier output is rail to rail.
Figure 73 shows the input and output waveforms of the
ADA4522-1/ADA4522-2/ADA4522-4 configured as a unity-
gain buffer with a supply voltage of ±15 V. With an input
voltage of ±15 V, the low output voltage tracks the input voltage,
whereas the high output swing clamps/distorts when the input
goes out of the input voltage range (−15 V ≤ IVR ≤ +13.5 V).
However, the device does not exhibit phase reversal.
20
0
–20
10
–10
20
0
–20
10
–10
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
TIME (400s/DIV)
V
SY
= ±15V
A
V
= 1
V
IN
V
OUT
13168-070
Figure 73. Input and Output Waveforms, No Phase Reversal
LARGE SIGNAL TRANSIENT RESPONSE
When the ADA4522-1/ADA4522-2/ADA4522-4 are configured
in a closed-loop configuration with a large input transient (for
example, a step input voltage), the internal back to back diodes may
turn on. Consider a case where the amplifier is in unity-gain
configuration with a step input waveform. This case is shown in
Figure 74.
The noninverting input is driven by an input signal source and
the inverting input is driven by the output of the amplifier. The
maximum amplifier output current depends on the input step
function and the external source resistance at the input
terminals of the amplifier.
Case 1
If the external source resistance is low (for example, 100 Ω in
Figure 75) or if the input step function is large, the maximum
amplifier output current is limited to the output short-circuit
current as specified in the Specifications section. The maximum
differential voltage between the input signal and the amplifier
output is then limited by the maximum amplifier output current
multiplied by the total input resistance (internal and external)
and the turn-on voltage of the back to back diode (see Figure 72
for the input EMI filter and clamp circuit architecture).
When the noninverting input voltage changes with a step signal,
the inverting input voltage (and, therefore, the output voltage)
follows the change quickly until it reaches the maximum differen-
tial voltage between the input signal and amplifier output possible.
The inverting input voltage then starts slewing with the slew
rate specified in the Specifications section until it reaches its
desired output. Therefore, as seen in Figure 74, there are two
distinctive sections of the rising and falling edge of the output
waveform. With this test condition, the amount and duration of
the input/output current is limited and, therefore, does not
damage the amplifier.
30
–30
–20
–10
0
10
20
VOLTAGE (V)
TIME (10µs/DIV)
V
SY
= ±27.5V
13168-071
Figure 74. Large Signal Transient Response Example
R
S_IN–
100
R
S_IN+
100
V
SY
+
V
SY
–
ADA4522-1/
ADA4522-2/
ADA4522-4
100pF 10k
V
OUT
V
IN
= 50V p-p
13168-100
Figure 75. Circuit Diagram for Large Signal Transient Response
Case 2
If the external source resistance is high or if the input step function
is small, the maximum output current is limited to the instantane-
ous difference between the input signal and amplifier output
voltage (which is the change in the step function) divided by the
source resistance. This maximum output current is less than the
amplifier output short-circuit current. The maximum differential
voltage between the input signal and the amplifier output is
then equal to the step function. The output voltage slews until it
reaches its desired output.
Therefore, if desired, reduce the input current by adding a larger
external resistor between the signal source and the noninverting
input. Similarly, to reduce output current, add an external resistor
to the feedback loop between the inverting input and output. This
large signal transient response issue is typically not a problem
when the amplifier is configured in closed-loop gain, where the
input signal source is usually much smaller and the gain and
feedback resistors limit the current.
Back to back diodes are also implemented in many other
amplifiers; these amplifiers show similar slewing behavior.
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