OPA3832_07 Datasheet, PDF (26/32 Pages) Burr-Brown (TI) – Triple, Low-Power, High-Speed, Fixed-Gain Operational Amplifier

OPA3832
SBOS370 – DECEMBER 2006
d) Connections to other wideband devices on the
board may be made with short direct traces or
through onboard transmission lines. For short
connections, consider the trace and the input to the
next device as a lumped capacitive load. Relatively
wide traces (50mils to 100mils) should be used,
preferably with ground and power planes opened up
around them. Estimate the total capacitive load and
set R_S from the typical characteristic curve, Figure 5.
Low parasitic capacitive loads (< 5pF) may not need
an R_S since the OPA3832 is nominally compensated
to operate with a 2pF parasitic load. Higher parasitic
capacitive loads without an R_S are allowed as the
signal gain increases (increasing the unloaded phase
margin). If a long trace is required, and the 6dB
signal loss intrinsic to a doubly-terminated
transmission line is acceptable, implement a
matched impedance transmission line using
microstrip or stripline techniques (consult an ECL
design handbook for microstrip and stripline layout
techniques). A 50Ω environment is normally not
necessary onboard, and in fact, a higher impedance
environment will improve distortion as shown in the
distortion versus load plots. With a characteristic
board trace impedance defined (based on board
material and trace dimensions), a matching series
resistor into the trace from the output of the
OPA3832 is used as well as a terminating shunt
resistor at the input of the destination device.
Remember also that the terminating impedance is
the parallel combination of the shunt resistor and the
input impedance of the destination device; this total
effective impedance should be set to match the trace
impedance. If the 6dB 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 shown in
the typical characteristic curve, Figure 5. This
configuration will not preserve signal integrity as well
as a doubly-terminated line. If the input impedance of
the destination device is low, there will be some
signal attenuation as a result of the voltage divider
formed by the series output into the terminating
impedance.
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e) Socketing a high-speed part is not
recommended. The additional lead length and
pin-to-pin capacitance introduced by the socket can
create an extremely troublesome parasitic network
that can make it almost impossible to achieve a
smooth, stable frequency response. Best results are
obtained by soldering the OPA3832 directly onto the
board.
INPUT AND ESD PROTECTION
The OPA3832 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 56.
+V_CC
External
Pin
Internal
Circuitry
-VCC
Figure 56. Internal ESD Protection
These diodes provide moderate protection to input
overdrive voltages above the supplies as well. The
protection diodes can typically support 30mA
continuous current. Where higher currents are
possible (that is, in systems with ±15V supply parts
driving into the OPA3832), 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.
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