ADA4522-4ARZ-R7 datasheet(23/32 Pages) AD

23 / 32 page

Data Sheet

ADA4522-1/ADA4522-2/ADA4522-4

Rev. E | Page 23 of 32

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

–10

–20

–10

TIME (400s/DIV)

VSY = ±15V

AV = 1

VIN

VOUT

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

–20

–10

TIME (10µs/DIV)

VSY = ±27.5V

Figure 74. Large Signal Transient Response Example

RS_IN–

100Ω

RS_IN+

100Ω

VSY+

VSY–

ADA4522-1/

ADA4522-2/

ADA4522-4

100pF

10kΩ

VOUT

VIN = 50V p-p

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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