2001-2012 Microchip Technology Inc. DS21482D-page 5
TC913A/TC913B
3.0 DETAILED DESCRIPTION
3.1 Theory of Operation
Each of the TC913’s two Op Amps actually consists of
two amplifiers. A main amplifier is always connected
from the input to the output. A separate nulling amplifier
alternately nulls its own offset and then the offset of the
amplifier. Since each amplifier is continuously being
nulled, offset voltage drift with time, temperature and
power supply variations is greatly reduced.
All nulling circuitry is internal and the nulling operation
is transparent to the user. Offset nulling voltages are
stored on two internal capacitors. An internal oscillator
and control logic, shared by the TC913’s two amplifiers,
control the nulling process.
3.2 Pin Compatibility
The TC913 pinout is compatible with OP-14, LM358,
MC1458, LT1013, TLC322, and similar dual Op Amps.
In many circuits operating from single or ±5V supplies,
the TC913 is a drop-in replacement offering DC
performance rivaling that of the best single Op Amps.
The TC913’s amplifiers include a low-impedance class
AB output buffer. Some previous CMOS chopper
amplifiers used a high-impedance output stage which
made open-loop gain dependent on load resistance.
The TC913’s open-loop gain is not dependent on load
resistance.
3.3 Overload Recovery
The TC913 recovers quickly from output saturation.
Typical recovery time from positive output saturation is
20 msec. Negative output saturation recovery time is
typically 5 msec.
3.4 Avoiding Latch-up
Junction-isolated CMOS circuits inherently contain a
parasitic p-n-p-n transistor circuit. Voltages exceeding
the supplies by 0.3V should not be applied to the
device pins. Larger voltages can turn the p-n-p-n
device on, causing excessive device power supply
current and power dissipation. The TC913’s power
supplies should be established at the same time or
before input signals are applied. If this is not possible,
input current should be limited to 0.1 mA to avoid
triggering the p-n-p-n structure.
