FS9721_LP3

Rev. 2.1

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15.14

Capacitance Measurement

R21

57.4k

R19

900k

RCAP

SMV

SGND

PTC

1k

Cap

COM

CX

FS9721_LP3

J3

J5

DO-

DO+

DO-

DO+

CMP

DO+

DO-

+

-

VDD

AGND

3/4VDD

1/4VDD

R31

10k

Input Typical Waveforms

3/4VDD

1/4VDD

VDD

Tdo

Diagram

31

Capacitance Measurement

Capacitance measurement is to charge/discharge the measuring capacitance through R21 to form a

oscillation, then calculate the cycle of oscillation to get the capacitance value. To adjust R21 can calibrate the

value in capacitance measurement. J3 and J5 are mode switches. When doing capacitance measurement, J3

and J5 are close.

15.15

Frequency Measurement

ADP

SGND

R29

1M

COM

Hz

FS9721_LP3

R27

100k

J6

J8

PTC

1k

R31

10k

C15

10uF

Diagram

32

Frequency Measurement