TLC4502IDR Datasheet, PDF (21/39 Pages) Texas Instruments – FAMILY OF SELF-CALIBRATING PRECISION CMOS RAIL-TO-RAIL OUTPUT OPERATIONAL AMPLIFIERS

TLC4501, TLC4501A, TLC4502, TLC4502A
FAMILY OF SELF-CALIBRATING (Self-Cal)
PRECISION CMOS RAIL-TO-RAIL OUTPUT OPERATIONAL AMPLIFIERS
SLOS221B – MAY 1998 – REVISED APRIL 2001
VDD
POWER-ON RESET
S
Q
ENABLE
RQ
RC
OSCILLATOR
COUNTER
RCO
CLOCK
RESET
SAR
CAL
DAC
–
CORE
AMPLIFIER
LPF
+
RCO
Figure 35. Block Diagram During Calibration Mode
The class AB output stage features rail-to-rail voltage swing and incorporates additional switches to put the
output node into a high-impedance mode during the calibration cycle. Small-replica output transistors (matched
to the main output transistors) provide the amplifier output signal for the calibration circuit. The TLC4502 also
features built-in output short-circuit protection. The output current flowing through the main output transistors
is continuously being sensed. If the current through either of these transistors exceeds the preset limit (60 mA
– 70 mA) for more than about 1 µs, the output transistors are shut down to approximately their quiescent
operating point for approximately 5 ms. The device is then returned to normal operation. If the short circuit is
still in place, it is detected in less than 1 µs and the device is shut down for another 5 ms.
The offset cancellation uses a current-mode digital-to-analog converter (DAC), whose full-scale current allows
for an adjustment of approximately ± 5 mV to the input offset voltage. The digital code producing the cancellation
current is stored in the successive-approximation register (SAR).
During power up, when the offset cancellation procedure is initiated, an on-chip RC oscillator is activated to
provide the timing of the successive-approximation algorithm. To prevent wide-band noise from interfering with
the calibration procedure, an analog low-pass filter followed by a Schmitt trigger is used in the decision chain
to implement an averaging process. Once the calibration procedure is complete, the RC oscillator is deactivated
to reduce supply current and the associated noise.
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