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PARAMETER MEASUREMENT INFORMATION

5 V

5.1 k

Ω

VO

Applied VIO

Limit

VO

5.1 k

Ω

1 V

−4 V

−

+

−

+

(a) VIO WITH VIC = 0

(b) VIO WITH VIC = 4 V

Applied VIO

Limit

TLC372-EP

LinCMOS™ DUAL DIFFERENTIAL COMPARATORS

SGLS385 – MARCH 2007

The digital output stage of the TLC372 can be damaged if it is held in the linear region of the transfer curve.

Conventional operational amplifier/comparator testing incorporates the use of a servo loop that is designed to

force the device output to a level within this linear region. Since the servo-loop method of testing cannot be

used, the following alternatives for measuring parameters such as input offset voltage, common-mode rejection,

etc., are offered.

To verify that the input offset voltage falls within the limits specified, the limit value is applied to the input as

shown in Figure 1(a). With the noninverting input positive with respect to the inverting input, the output should be

high. With the input polarity reversed, the output should be low.

A similar test can be made to verify the input offset voltage at the common-mode extremes. The supply voltages

can be slewed as shown in Figure 1(b) for the VICR test, rather than changing the input voltages, to provide

greater accuracy.

Figure 1. Method for Verifying That Input Offset Voltage is Within Specified Limits

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 states.

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