TLC339IPW Datasheet, PDF (8/30 Pages) Texas Instruments – LinCOMS MICROPOWER QUAD COMPARATORS

TLC139, TLC339, TLC339Q
LinCMOS MICROPOWER QUAD COMPARATORS
PARAMETER MEASUREMENT INFORMATION
A close approximation of the input offset voltage can be obtained by using a binary search method to vary the
differential input voltage while monitoring the output state. When the applied input voltage differential is equal but
opposite in polarity to the input offset voltage, the output changes state.
Figure 2 illustrates a practical circuit for direct dc measurement of input offset voltage that does not bias the
comparator into the linear region. The circuit consists of a switching mode servo loop in which U1A generates a
triangular waveform of approximately 20-mV amplitude. U1B acts as a buffer, with C2 and R4 removing any residual
dc offset. The signal is then applied to the inverting input of the comparator under test, while the noninverting input
is driven by the output of the integrator formed by U1C through the voltage divider formed by R9 and R10. The loop
reaches a stable operating point when the output of the comparator under test has a duty cycle of exactly 50%, which
can only occur when the incoming triangle wave is sliced symmetrically or when the voltage at the noninverting input
exactly equals the input offset voltage.
Voltage divider R9 and R10 provides a step-up of the input offset voltage by a factor of 100 to make measurement
easier. The values of R5, R8, R9, and R10 can significantly influence the accuracy of the reading; therefore, it is
suggested that their tolerance level be 1% or lower.
C1
0.1 µF
U1B
1/4 TLC274CN
+ ^Buffer
−
C2
1 µF
R1
240 kΩ
R4
47 kΩ
U1A
− ^{1/4 TLC274CN}
+
Triangle
Generator
R2
R3 ^{10 kΩ}
100 kΩ
VDD
R5
1.8 kΩ, 1%
R3
5.1 kΩ
Dut
R7
1 MΩ
R8
1.8 kΩ, 1%
R9
R10
10 kΩ, 1%
100 Ω, 1%
C3 0.68 µF
U1C
1/4 TLC274CN
−
+
Integrator
C4
0.1 µF
VIO
(X100)
Figure 2. Circuit for Input Offset Voltage Measurement
Measuring the extremely low values of input current requires isolation from all other sources of leakage current and
compensation for the leakage of the test socket and board. With a good picoammeter, the socket and board leakage
can be measured with no device in the socket. Subsequently, this open socket leakage value can be subtracted from
the measurement obtained, with a device in the socket to obtain the actual input current of the device.
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