FS9952_LP2

R14 10k

R28

99

R27

0.99

R26

0.01

J5

J4

uA/mA

20A

FS9952

0.5A/250V

20A/250V

1N4004*2

COM

5 SA

30 AGND

Diagram 27

Current Measurement

When doing the current measurement, the current signals enter IC through R14.

The sampling resistance of μA mode is R26+R27+R28, the sampling resistance of mA mode is R27+R26 and

the sampling resistance of 20A mode is R26. They are measured respectively through the mode switch. When

measuring μA, J4 is open, and J5 is close; when measuring mA, J14 is close, and J5 is open; when measuring

the large current of 20A mode, the current enter directly from 20A port.

The maximum reduced voltage for μA, mA and 10A modes is 0.2V.

These voltages are input voltage comparator to compare. If the voltage is smaller than 20mV, it will be sent to

10 times amplifier to amplify, then sent to A/D converter; if the voltage is larger than 20mV, the system will act

the auto jump mode to jump up one mode under the control of the microprocessor, and then send directly the

current signal into A/D converter.

Rev. 1.2

28/34