DA1641.004

1 February, 2019

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APPLICATION INFORMATION (continued)

TEST output for determining sensed input capacitance value

MAS1641 has open drain output TEST pin. By connecting 4.7k

 pull-up resistor from TEST output to VIN it is

possible to determine measured input capacitance by analyzing the TEST output signal using an oscilloscope (see

figure 3 for measurement configuration). This is useful feature when not knowing exact values of the sensed input

capacitances.

Figure 3. TEST output monitoring circuit for determining sensed input capacitance value

reference measurement which lasts typically 0.1s. Counter reset period lasts 0.1s and which is followed by 0.1s

monitoring measurement. After this the counter reset and monitoring measurement are repeated in 2s period. See

flow graph in the figure 2.

During reference and every monitoring measurement the measurement oscillator signal is transmitted to the TEST

output. Thus after power up there is seen first 0.1s long burst of reference measurement oscillator pulses and after

0.1s delay another 0.1s burst of monitoring measurement oscillator pulses. Figure 4 presents measured TEST pin

signal after power up. It shows the reference and the first monitoring measurement signal bursts.