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AD8571/AD8572/AD8574

Data Sheet

Rev. F | Page 20 of 28

CAPACITIVE LOAD DRIVE

The AD8571/AD8572/AD8574 have excellent capacitive load

driving capabilities and can safely drive up to 10 nF from a

single 5 V supply. Although the device is stable, capacitive

loading limits the bandwidth of the amplifier. Capacitive loads

also increase the amount of overshoot and ringing at the output.

The RC snubber network shown in Figure 59 can be used to

reduce the capacitive load ringing and overshoot.

VOUT

VIN

200mV p-p

AD8571/

AD8572/

AD8574

4.7nF

0.47µF

Ω

–

Figure 59. Snubber Network Configuration for Driving Capacitive Loads

Although the snubber network does not recover the loss of

amplifier bandwidth from the load capacitance, it does allow

the amplifier to drive larger values of capacitance while

maintaining a minimum of overshoot and ringing. Figure 60

shows the output of an AD8571/AD8572/AD8574 driving a

1 nF capacitor with and without a snubber network.

10μs

100mV

VS = 5V

CL = 4.7nF

WITHOUT

SNUBBER

WITH

SNUBBER

Figure 60. Overshoot and Ringing Are Substantially Reduced Using

a Snubber Network

The optimum value for the resistor and capacitor is a function

of the load capacitance and is best determined empirically

because actual CL includes stray capacitances and can differ

substantially from the nominal capacitive load. Table 5 shows

some snubber network values that can be used as starting points.

Table 5. Snubber Network Values for Driving Capacitive Loads

CL (nF)

Rx (Ω)

200

1 nF

4.7

0.47 µF

10 µF

POWER-UP BEHAVIOR

At power-up, the AD8571/AD8572/AD8574 settle to a valid

output within 5 μs. Figure 61 shows an oscilloscope photo of the

output of the amplifier along with the power supply voltage.

Figure 62 shows the test circuit. With the amplifier configured

for unity gain, the device takes approximately 5 µs to settle to its

final output voltage, hundreds of microseconds faster than

many other autocorrection amplifiers.

5µs

VOUT

V+

BOTTOM TRACE = 2V/DIV

TOP TRACE = 1V/DIV

Figure 61. AD8571/AD8572/AD8574 Output Behavior at Power-Up

100kΩ

VSY = 0V TO 5V

VOUT

AD8571/

AD8572/

AD8574

Figure 62. AD8571/AD8572/AD8574 Test Circuit for Power-Up Time

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