FS9952_LP1

Rev. 2.0

27/31

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.

15.13 Resistance Measurement

R23 10M

R22 1.111M

R21 101.01k

R20 10k

R19 1k

R18 100k

R15 10k

Rx

J8

J6

Ohm

COM

15 TENM

14 ONEM

13 HUNK

12 TENK

11 ONEK

10 RL

6 SGND

FS9952

AGND

PTC

1.5k

9 CRES1

C11

27nF

R17 900k

8 SMV

Diagram 28

Resistance Measurement

Resistance measurement refers to standard resistance, and then takes a comparison between measuring

resistance and standard resistance to get the measuring resistance value. The standard resistance of 20MΩ

mode is 10MΩ (R23). The standard resistance of other modes are R23 to parallel respectively with R22, R21,

R20 and R19 to get 1MΩ, 100kΩ, 10kΩ, 1kΩ resistance. When doing resistance measurement, internal IC will

generate 0.4V voltage (relative to AGND), the voltage is output respectively to measuring resistance to

compare through resistance R23, R22, R21, R20 and R19. R18 connects to RL, which is the negative input of

the voltage reference that is gotten by the standard resistance. J3 and J5 are mode switches. When doing

resistance measurement, J6 and J8 are close. C11 is the wave filter capacitance of measuring point in

resistance measurement.

15.14

Diode Test

15 TENM

11 ONEK

8 SMV

7 DT

6 SGND

FS9952

J8

J6

VD

Diode

COM

PTC

1.5k

R23

10M

R19

1k

R17

900k

R16

100k

R15

10k

Diagram 29

Diode Measurement

Diode test generates 1.5V voltage from internal IC and outputs it through R19, then adds it to the positive

of diode through PTC. The positive voltage reduction VD generated by diode is approx. 0.5V-0.7V. VD is

divided by R17 and R16 to be 1/10 VD, then is amplified 10 times by internal OP and is delivered to A/D before

displaying the VD value. J6 and J8 are mode switches. When doing diode measurement, J6 and J8 are close.