OPA835IDBVT datasheet(34/53 Pages) NSC

34 / 53 page

OPA835

330 pF

562 W

6.19 kW

2.2 nF

OPA 835

220 pF

1.82 kW

4.22 kW

1.5 nF

OPA835

OUT

2 kW

OPA835

OPA2835

SLOS713E – JANUARY 2011 – REVISED JULY 2013

www.ti.com

Driving Capacitive Loads

The OPA835 and OPA2835 can drive up to a nominal capacitive load of 10pF on the output with no special

consideration. When driving capacitive loads greater than this, it is recommended to use a small resister (RO) in

series with the output as close to the device as possible. Without RO, capacitance on the output will interact with

the output impedance of the amplifier causing phase shift in the loop gain of the amplifier that will reduce the

phase margin. This will cause peaking in the frequency response and overshoot and ringing in the pulses

response. Interaction with other parasitic elements may lead to instability or oscillation. Inserting RO will isolate

the phase shift from the loop gain path and restore the phase margin; however, it will also limit the bandwidth.

Figure 71 shows the test circuit and Figure 41 shows the recommended values of RO versus capacitive loads,

CL. See Figure 40 for frequency response with various values.

Figure 71. RO versus CL Test Circuit

Active Filters

The OPA835 and OPA2835 can be used to design active filters. Figure 73 and Figure 72 show MFB and Sallen-

Key circuits designed using FilterPro™ http://focus.ti.com/docs/toolsw/folders/print/filterpro.html to implement 2nd

order low-pass butterworth filter circuits. Figure 74 shows the frequency response.

Figure 72. MFB 100kHz 2nd Order Low-Pass Butterworth Filter Circuit

Figure 73. Sallen-Key 100kHz 2nd Order Low-Pass Butterworth Filter Circuit

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OPA835IDBVT Datasheet(PDF) 34 Page - National Semiconductor (TI)