+

NEUTRAL

GFCI

system

S1

-

S3

RN = 0.4

RG= 1.6

+

-

HOT

21

AFE3010

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SBFS042 – JUNE 2020

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Figure 16. Neutral-to-Ground Detection Test Setup for AFE3010 Design Procedure

b. Choose the RN and RG pair that creates the largest total resistance, as this is the worst-case for the

AFE3010's N-G detection. In this procedure, the total N-G resistance to test is 2 Ω.

c. Using the relays S1 and S3, switch in the N-G fault and check if the system trips. Note that either relay

may be closed first.

d. If the system successfully trips, then re-test the detection over temperature.

e. If the system successfully detects N-G fault overtemperature, then the first-pass component optimization

is complete.

f.

If the system fails to detect the N-G, then consider the following component modifications:

i.

Adjust R6. Decreasing R6 has shown to increase the N-G pulse sensed by amplifier with minimal

effect on amplifier gain.

ii. Increase R7. The trip point must be checked again because the amplifier gain will increase.

iii. Reduce the NG_OUT resistor R5. Note that there is a lower bound to the value of R5, depending on

the impedance of the 200-turn coil. R5 helps limit current from any activated internal ESD cells

during the inductive kickback on the NG_OUT pin. If R5 must be decreased, consider adding a

Schottky diode at the NG_OUT pin to clamp the NG_OUT voltage above the Absolute Maximum

Rating of –0.3 V.

iv. Add a small capacitor from the REF pin to GND. Values between 100 pF and 300 pF are acceptable.

5. Successful operation of the AFE3010 can be seen with the successful passing of the internal self-tests. A

successful self-test can be observed with the ALARM LED (D3) blinking once one second after device power

up.

6. Perform the rest of the testing specified in the UL-943 standard.