OPA2832 Datasheet, PDF (27/37 Pages) National Semiconductor (TI) – Dual, Low-Power, High-Speed, Fixed-Gain Operational Amplifier

OPA2832
www.ti.com ............................................................................................................................................. SBOS327C – FEBRUARY 2005 – REVISED AUGUST 2008
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
Recommended R_S vs Capacitive Load. Low parasitic
capacitive loads (< 5pF) may not need an R_S since
the OPA2832 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 OPA2832 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
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 Recommended R_S vs
Capacitive Load. This 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 due to the voltage divider
formed by the series output into the terminating
impedance.
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
which can make it almost impossible to achieve a
smooth, stable frequency response. Best results are
obtained by soldering the OPA2832 onto the board.
INPUT AND ESD PROTECTION
The OPA2832 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 72.
+V_CC
External
Pin
Internal
Circuitry
− V_CC
Figure 72. 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 OPA2832), 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.
Copyright © 2005–2008, Texas Instruments Incorporated
Product Folder Link(s): OPA2832
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