OPA838IDBVT datasheet(22/41 Pages) TI1

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RF 1

NŸ

RG 200

VOUT

VEE

VCC

VEE

VCC

V1 2.5

±2.5 Ÿ

VG1

ROUT 68.1

Frequency (Hz)

-15

-12

-9

-6

-3

10k

100k

10M

100M

D070

No caps

With caps

OPA838

SBOS867 – AUGUST 2017

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Product Folder Links: OPA838

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Feature Description (continued)

Figure 65. Inverting Response With and Without Compensation

8.3.5 Driving Capacitive Loads

The OPA838 can drive small capacitive loads directly without oscillation (less than 6 pF). When driving capacitive

loads greater than 6 pF, Figure 49 shows the recommended ROUT vs capacitor load parametric on gains. At

higher gains, the amplifier starts with greater phase margin into a resistive load and can operate with lower ROUT

for a given capacitive load. Without ROUT, output capacitance interacts with the output impedance of the

amplifier, which causes phase shift in the loop gain of the amplifier that reduces the phase margin. This causes

peaking in the frequency response with overshoot and ringing in the pulse response. Figure 49 targets a 30°

phase margin for the OPA838. A 30° phase margin produces a 5.7-dB peaking in the frequency response at the

amplifier output pin that is rolled off by the output RC pole, as shown in Figure 67. This peaking can cause

clipping for large signals driving a capacitive load. Increasing the RO value can reduce the peaking at the cost of

a more band-limited overall response.

Figure 66. RO versus CL Test Circuit

OPA838IDBVT Datasheet(PDF) 22 Page - Texas Instruments

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