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SBOS099C − SEPTEMBER 2000 − REVISED JANUARY 2005
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V+
Reference
Current
VIN+
−
VIN
VBIAS1
Class AB
Control
VO
Circuitry
VBIAS2
−
V
(Ground)
Figure 2. Simplified Schematic
within a few tens of millivolts from the supply rails and
maintain high open-loop gain. See the typical
characteristics Output Voltage Swing vs Output Current
and Open-Loop Gain vs Output Voltage.
V+
CAPACITIVE LOAD AND STABILITY
IOVERLOAD
10mA max
OPA350 series op amps can drive a wide range of
capacitive loads. However, all op amps under certain
conditions may become unstable. Op amp
configuration, gain, and load value are just a few of the
factors to consider when determining stability. An op
amp in unity-gain configuration is the most susceptible
to the effects of capacitive load. The capacitive load
reacts with the op amp’s output impedance, along with
any additional load resistance, to create a pole in the
small-signal response that degrades the phase margin.
VOUT
OPAx350
VIN
Ω
5k
Figure 3. Input Current Protection for Voltages
Exceeding the Supply Voltage
In unity gain, OPA350 series op amps perform well with
very large capacitive loads. Increasing gain enhances
the amplifier’s ability to drive more capacitance. The
typical characteristic Small-Signal Overshoot vs
Capacitive Load shows performance with a 1kΩ
resistive load. Increasing load resistance improves
capacitive load drive capability.
RAIL-TO-RAIL OUTPUT
A class AB output stage with common-source
transistors is used to achieve rail-to-rail output. For light
resistive loads (>10kΩ), the output voltage swing is
typically ten millivolts from the supply rails. With heavier
resistive loads (600Ω to 10kΩ), the output can swing to
10
BB [ BURR-BROWN CORPORATION ]
