TS321
Low Power Single Operational Amplifier
Document Number: DS_P0000227
3
Version: B15
Application Hints
The TS321 OP amp can operate with a single or dual power supply voltage has true-differential inputs, and remain in
he linear mode with an input common-mode voltage of 0 V
DC
. This amplifier operates over a wide range of power
supply voltages, with little change in performance characteristics .At 25
o
C amplifier operation is possible down to a
minimum supply voltage of 3V.
Large differential input voltage can be easily accommodates and, as input differential voltage protection diodes are not
needed, no large input currents result from large differential input voltage. The differential input voltage may be larger
than V
+
without damaging the device. Protection should be provided to prevent the input voltage from going negative
more than –0.3 V
DC
(at 25
o
C).
An input clamp diode with a resistor to the IC input terminal can be used.
To reduce the power supply drain, the amplifier has a class A output stage for small signal levels which converts to
class B in a large signal mode. This allows the amplifiers to both source and sink large output currents. Therefore both
NPN and PNP external current boots transistor can be used to extend the power capability of the basic amplifiers. The
output voltage needs to raise approximately 1 diode drop above ground to bias the on-chip vertical PNP transistor for
output current sinking applications.
For AC applications, where the load is capacitively coupled to the output of the amplifier, a resistor should be used,
from the output of the amplifier to ground to increase the class A bias current and to reduce distortion. Capacitive loads
which are applied directly to the output of the amplifier reduce the loop stability margin. Values of 50pF can be
accommodated using the worst-case non-inverting unity gain connection. Large closed loop gains or resistive isolation
should be used if large load capacitance must be driven by the amplifier
The bias network of the TS312 establishes a supply current which is independent of the magnitude of the magnitude of
the power supply voltage over the range of from 3V
DC
to 3V
DC.
Output short circuits either to ground or to the positive power supply should be of short time duration. Units can be
destroyed , not as a result of the short circuit current causing metal fusing, but rather due to the large increase in IC
chip dissipation which cause eventual failure due to excessive junction temperatures. The large value of output source
current which is available at 25
o
C, provides a large output current capability at elevated temperature than a standard IC
op amp.
The circuits presented in the section on typical applications emphasize operation on only a single power supply voltage.
If complementary power supplies are available, all of the standard op amp circuits can be used. In general, introducing
a pseudo-ground (a bias voltage reference of V
+
/2) will allow operation above and below this value in single power
supply systems. Many application circuits are shown which take advantage of the wide input common-mode voltage
range which includes ground. In most cases, input biasing is not required and input voltage which range to ground can
easily be accommodated.
Typical Applications
Figure 1. LED Driver
Figure 2. Lamp Driver
