Data Sheet

ADA4522-1/ADA4522-

2/ADA4522-4

analog.com

Rev I 36 of 48

Figure 79.EMIRR vs. Frequency

Capacitive Load Stability

The ADA4522-1/ADA4522-2/ADA4522-4 can safely drive capacitive loads of up to 250 pF in any configuration. As with

most amplifiers, driving larger capacitive loads than specified may cause excessive overshoot and ringing, or even

oscillation. A heavy capacitive load reduces the phase margin and causes the amplifier frequency response to peak.

Peaking corresponds to overshooting or ringing in the time domain. Therefore, it is recommended that external

compensation be used if the ADA4522-1/ADA4522-2/ADA4522-4 must drive a load exceeding 250 pF. This

compensation is particularly important in the unity-gain configuration, which is the worst case for stability.

A quick and easy way to stabilize the op amp for capacitive load drive is by adding a series resistor, RISO, between the

amplifier output terminal and the load capacitance, as shown in Figure 80. RISO isolates the amplifier output and

feedback network from the capacitive load. However, with this compensation scheme, the output impedance as

seen by the load increases, and this reduces gain accuracy.

Figure 80.Stability Compensation with Isolating Resistor, RISO

Figure 81

shows the effect on overshoot with different values of RISO.

100

50

90

40

80

30

70

20

60

10

0

10M

100M

1G

10G

FREQUENCY (Hz)

55V

30V

5V

VIN = 100mV p-p

–VSY

VIN

+VSY

VOUT

CL

ADA4522-1/

ADA4522-2/

ADA4522-4

RISO

60

25

50

55

45

20

40

15

35

10

30

5

0

10

100

1k

LOAD CAPACITANCE (pF)

VSY = ±15V

RL = 10kΩ

AV = 1

VIN = 100mV p-p

OS+ (RISO = 0Ω)

OS– (RISO = 0Ω)

OS+ (RISO = 25Ω)

OS– (RISO = 25Ω)

OS+ (RISO = 50Ω)

OS– (RISO = 50Ω)

Figure 81.Small Signal Overshoot vs. Load Capacitance with Various Output Isolating Resistors