FS9721B

Rev. 1.7

28/

35

15.16 Short Circuit Testing

J5

J3

FS9721B

TENM

ONEK

SMV

SGND

AGND

PTC

1k

Continuity

COM

R26 10M

R22 1k

R19 900k

Rx

R27 10k

Diagram 29

Short Circuit Testing

Short circuit testing is proceeded in 240Ωresistance mode. 0.4V voltage (relative to AGND) is generated by

internal IC and output through R22, then add to short measuring point through PTC. J3 and J5 are mode switch

than 50Ω, the beeper will sound.

15.17 Capacitance Measurement

R21

57.4k

R19

900k

RCAP

SMV

SGND

PTC

500

Cap

COM

CX

FS9721B

J3

J5

DO-

DO+

DO-

DO+

CMP

DO+

DO-

+

-

VDD

AGND

3/4VDD

1/4VDD

R27

10k

Typical Wave of Input End

3/4VDD

1/4VDD

VDD

Tdo

Diagram 30

Capacitance Measurement

Capacitance measurement is to charge/discharge to 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 switch. When doing capitance measurement, J3 and

J5 are close.

(In actual application, if the linearity is worse when doing 2.5nF measurement, you can take a consideration of

paralleling a proximate 1000pF capacitance in input end of capacitance measurement during design. When

doing the measurement, to press REL key and make the value be zero before measuring. The linearity of the

smaller measurement in capacitance mode will be better.)