OPA3832_07 Datasheet, PDF (23/32 Pages) Burr-Brown (TI) – Triple, Low-Power, High-Speed, Fixed-Gain Operational Amplifier

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DESIGN-IN TOOLS
DEMONSTRATION FIXTURES
Two printed circuit boards (PCBs) are available to
assist in the initial evaluation of circuit performance
using the OPA3832 in its two package options. Both
of these are offered free of charge as unpopulated
PCBs, delivered with a user's guide. The summary
information for these fixtures is shown in Table 1.
Table 1. Demonstration Fixtures by Package
PRODUCT
OPA3832ID
OPA3832IPW
PACKAGE
SO-14
TSSOP-14
ORDERING
NUMBER
LITERATURE
NUMBER
DEM-OPA-SO-3B
SBOU018
DEM-OPA-SSOP-3B SBOU019
The demonstration fixtures can be requested at the
Texas Instruments web site (www.ti.com) through the
OPA3832 product folder.
MACROMODEL AND APPLICATIONS
SUPPORT
Computer simulation of circuit performance using
SPICE is often a quick way to analyze the
performance of the OPA3832 and its circuit designs.
This is particularly true for video and RF amplifier
circuits where parasitic capacitance and inductance
can play a major role on circuit performance. A
SPICE model for the OPA3832 is available through
the TI web page (www.ti.com). The applications
department is also available for design assistance.
These models predict typical small signal ac,
transient steps, dc performance, and noise under a
wide variety of operating conditions. The models
include the noise terms found in the electrical
specifications of the data sheet. These models do
not attempt to distinguish between the package types
in their small-signal ac performance.
OPERATING SUGGESTIONS
OUTPUT CURRENT AND VOLTAGES
The OPA3832 provides outstanding output voltage
capability. For the +5V supply, under no-load
conditions at +25°C, the output voltage typically
swings closer than 90mV to either supply rail.
The minimum specified output voltage and current
specifications over temperature are set by
worst-case simulations at the cold temperature
extreme. Only at cold startup will the output current
and voltage decrease to the numbers shown in the
ensured tables. As the output transistors deliver
power, the junction temperatures will increase,
decreasing the V_BEs (increasing the available output
voltage swing) and increasing the current gains
(increasing the available output current). In
OPA3832
SBOS370 – DECEMBER 2006
steady-state operation, the available output voltage
and current will always be greater than that shown in
the over-temperature specifications, because the
output stage junction temperatures will be higher
than the minimum specified operating ambient.
To maintain maximum output stage linearity, no
output short-circuit protection is provided. This
configuration will not normally be a problem, since
most applications include a series matching resistor
at the output that will limit the internal power
dissipation if the output side of this resistor is shorted
to ground. However, shorting the output pin directly
to the adjacent positive power-supply pin (8-pin
packages) will, in most cases, destroy the amplifier.
If additional short-circuit protection is required,
consider a small series resistor in the power-supply
leads. This resistor will reduce the available output
voltage swing under heavy output loads.
DRIVING CAPACITIVE LOADS
One of the most demanding and yet very common
load conditions for an op amp is capacitive loading.
Often, the capacitive load is the input of an
Analog-to-Digital Converter (ADC)—including
additional external capacitance which may be
recommended to improve ADC linearity. A
high-speed, high open-loop gain amplifier like the
OPA3832 can be very susceptible to decreased
stability and closed-loop response peaking when a
capacitive load is placed directly on the output pin.
When the primary considerations are frequency
response flatness, pulse response fidelity, and/or
distortion, the simplest and most effective solution is
to isolate the capacitive load from the feedback loop
by inserting a series isolation resistor between the
amplifier output and the capacitive load.
The Typical Characteristic curves show the
recommended R_S versus capacitive load and the
resulting frequency response at the load. Parasitic
capacitive loads greater than 2pF can begin to
degrade the performance of the OPA3832. Long
PCB traces, unmatched cables, and connections to
multiple devices can easily exceed this value. Always
consider this effect carefully, and add the
recommended series resistor as close as possible to
the output pin (see the Board Layout Guidelines
section).
The criterion for setting this R_S resistor is a maximum
bandwidth, flat frequency response at the load. For a
gain of +2, the frequency response at the output pin
is already slightly peaked without the capacitive load,
requiring relatively high values of R_S to flatten the
response at the load. Increasing the noise gain will
also reduce the peaking.
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