External

Pin

+V

CC

−V

CC

O PA820

+5V

−5V

50Ω

50Ω

Power−supply

decoupling not shown.

174Ω

D1

D2

V

1

R

G

301Ω

50Ω

R

F

301Ω

V

O

D1 = D2 IN5911 (or equivalent)

50Ω Source

OPA820-HT

SBOS587

– DECEMBER 2011

www.ti.com

board material and trace dimensions, a matching series resistor into the trace from the output of the OPA820

is used as well as a terminating shunt resistor at the input of the destination device. Remember also that the

terminating impedance will be the parallel combination of the shunt resistor and input impedance of the

destination device; this total effective impedance should be set to match the trace impedance. If the 6-dB

attenuation of a doubly-terminated transmission line is unacceptable, a long trace can be series-terminated

at the source end only. Treat the trace as a capacitive load in this case and set the series resistor value as

doubly-terminated line. If the input impedance of the destination device is low, there will be some signal

attenuation due to the voltage divider formed by the series output into the terminating impedance.

e. Socketing a high-speed part like the OPA820 is not recommended. The additional lead length and

pin-to-pin capacitance introduced by the socket can create an extremely troublesome parasitic network,

which can make it almost impossible to achieve a smooth, stable frequency response. Best results are

obtained by soldering the OPA820 onto the board.

Input and ESD Protection

The OPA820 is built using a very high-speed complementary bipolar process. The internal junction breakdown

voltages are relatively low for these very small geometry devices. These breakdowns are reflected in the

Absolute Maximum Ratings table. All device pins are protected with internal ESD protection diodes to the power

supplies, as shown in Figure 13.

Figure 13. Internal ESD Protection

These diodes provide moderate protection to input overdrive voltages above the supplies as well. The protection

diodes can typically support 30-mA continuous current. Where higher currents are possible (for example, in

systems with

±15-V supply parts driving into the OPA820), current-limiting series resistors should be added into

the two inputs. Keep these resistor values as low as possible since high values degrade both noise performance

and frequency response. Figure 14 shows an example protection circuit for I/O voltages that may exceed the

supplies.

Figure 14. Gain of +2 With Input Protection

28

Submit Documentation Feedback

Copyright

© 2011, Texas Instruments Incorporated

Product Folder Link(s): OPA820-HT