FS9721_LP1 datasheet(29/41 Pages) FORTUNE

29 / 41 page

FS9721_LP1

Rev. 2.0

30/41

14.13 Current Measurement

The difference between Current Measurement（A）and Current Measurement（B） is as follow:

Mode

Current Measurement

（A）

Current Measurement

（B）

ADPC1 Open

ADPC1 connects to

VSS

Measureme

Sampling

Resistanc

Measureme

Sampling

Resistanc

40A

0.01Ω

40A

0.01Ω

400mA

40mA

10Ω

400mA

40mA

1Ω

μA

4000μA

400μA

1kΩ

4000μA

400μA

100Ω

Max.

Voltage

Reduction

0.4V

J11

J10

uA/mA

10A

FS9721_LP1

0.5A/250V

10A/250V

COM

SMV

SGND

R17

990

R16

9.99

R29

0.01

R18

10k

R20

900k

R19

100k

Diagram 26

Current Measurement(A)

In TSTB open mode, the current signal enters IC from R20.

When doing the current measurement,The sampling resistance of μA mode is (R16+R17+R29),

the sampling resistance of mA mode is (R16+R29) and the sampling resistance of 10A mode is R29.

They are measured respectivly through the mode switch. When measuring μA, J10 is open, J11 and

J3 is close; when measuring mA, J11 is open, J10 and J3 is close; when measuring the large

current by using 10A mode, J3 is close.

The maximum reduced voltage for μA, mA and 10A modes is 4V. These voltages are input

voltage comparator to compare. If the voltage is smaller than 400mV, the current signal is sent

directly to the A/D converter; if the voltage is larger than 400mV, the system will jump up one mode

and divide the voltage by R20 and R19, then send its 1/10 to the A/D converter.

The accuracy of resistor R16, R17, R29, R19 and R20 influence the accuracy of the current

measurement.

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