Datasheet

OPA835
330 pF
562 W
6.19 kW
2.2 nF
OPA835
220 pF
1.82 kW
1.82 kW 4.22 kW
1.5 nF
OPA835
V
IN
V
OUT
R
O
C
L
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 (R
O
) in
series with the output as close to the device as possible. Without R
O
, 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 R
O
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 R
O
versus capacitive loads,
C
L
. See Figure 40 for frequency response with various values.
Figure 71. R
O
versus C
L
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 2
nd
order low-pass butterworth filter circuits. Figure 74 shows the frequency response.
Figure 72. MFB 100kHz 2
nd
Order Low-Pass Butterworth Filter Circuit
Figure 73. Sallen-Key 100kHz 2nd Order Low-Pass Butterworth Filter Circuit
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