FS9721_LP3

Rev. 2.1

28/39

15.9

Voltage Measurement

VR1

10k

PTC

1k

REFI

REFO

TENM

ONEM

HUNK

TENK

ONEK

SGND

FS9721_LP3

COM

V

V

R8 40k

R620k

R25 1.111M

R24 101.01k

R23

10k

R22

1k

R26 10M

R31

10k

Diagram 24

Voltage Measurement

When doing the voltage measurement, the measuring voltage is input from resistance R26 and DCmV is

not divided but enter IC directly; the voltages of 4V, 40V, 400V, 1000V modes are divided by R25, R24, R23,

R22 and R26 to gain 1/10, 1/100, 1/1000, 1/10000 input voltages, then enter IC. To adjust the resistance value

of VR1 can do the calibration of the measurement.

The voltage division diagram of voltage measurement is as below:

Vout=0.1V

Vout=0.1V

Vout=0.1V

Vout=0.1V

Vin=1V

Vin=10V

Vin=100V

Vin=1000V

R26

10M

R26

10M

R26

10M

R26

10M

R25

1.111M

R24

101.01k

R23

10k

R22

1k

Diagram 25

Voltage Division Circuitry

The formula of voltage division is:

Vout=Vin x [Rs/（R26+Rs）]

Rs is R25, R24, R23 or R22.

Therefore, the accuracy of R22, R23, R24, R25 and R26 decides the accuracy of the measurement.

ACmV Voltage enters IC through R26 and is divided by R25 and R26 to get 1/10 voltage, then is amplified

10 times to fulfill the measurement, so the accuracy of R9 and R7 also determines the measuring accuracy of

AcmV voltage.