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AFE3010

SBFS042 – JUNE 2020

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Table 5. Summary of Components in AFE3010 Typical Application (continued)

COMPONENT

DESIGNATOR

COMPONENT

VALUE

COMPONENT

RATINGS

DESCRIPTION

R8

10.5 kΩ

1%, 0.5 W

Sets the level of fault current used in the periodic self-test when Q1 is

turned on. The fault current should be greater than the trip point for

successful detection and operation. The self-test will be hardest to pass

when line connects to GFCI with reverse polarity and there is a small

leakage current that is below the trip current. The worst-case power

condition will be when a device cannot detect the self-test fault current

and thus Q1 is on for a half-cycle of line.

R9

1.5 kΩ

5%, 0.1 W

Limits the output current of the ALARM driver. Using a higher R9 value

will reduce supply current when ALARM is driving D3.

R10

560 Ω

5%, 0.1 W

Limits the output current of the SCR driver.

R11

51 kΩ

5%, 1/3 W

Limits the current into the SCR_TST pin when regulating to 20 V and sets

internal biasing. The value of the resistor should not change from the

recommendation when SEL = LOW. The lowest acceptable value is a 1%

49.9 kΩ. Given a 170-V peak line voltage, the average power rating

required is calculated with [((170 V – 20 V)2) /R11] / [2 × SQRT(2)].

R12

1 MΩ

5%, 0.1 W

Limits the current into PH pin.

WARNING

When evaluating this device, implement high-voltage safety precaution and

procedures.

1. The first step in the design of a system with AFE3010 is to determine the correct transformer orientation and

coil connections. The AFE3010 internal detection scheme requires the fault waveforms to have a specific

polarity to the Hot-to-Neutral line voltage. The two rules the design must follow are:

a. The amplifier output voltage (VOUT) must be approximately 180° out of phase with the Hot-Neutral line

voltage when line voltage connects to a GFCI unit with normal polarity. Thus, when line is connected to

system with reverse polarity, the VOUT signal must be in-phase with line voltage. The amplifier's polarity

is determined by the value of C3, the connection of amplifier inputs (REF and FB) to the 1000-turn coil,

and by the direction of the line wires through the transformer core. Refer to Figure 17 for the correct

waveform. Note that normal line polarity means that the Hot and neutral nodes of the source are

connected correctly to the Hot and Neutral input connectors of the system, respectively, which means the

PH pin and D4 are also connected to Hot as shown in Figure 15.

b. The N-G pulse on VOUT when there is a N-G fault must look like Figure 18. The N-G pulse measured on

VOUT should first increase above 2.5 V and then decrease below 2.5 V. The second, downward pulse

should be greater in amplitude and energy than the initial positive pulse. This rule should be true

regardless of line polarity. N-G pulse polarity is determined by the connection of NG_OUT and GND pins

to the 200-turn coil and by the polarity of the line wires through the transformer core.

2. Populate the board with the recommended values shown in Table 5.

3. Tune the amplifier's ground fault threshold (trip point).

a. Set up the system with an adjustable Hot-to-ground (H-G) fault load and an ammeter in-series to

measure the fault (or leakage) current.

b. Adjust the fault load so that the ammeter reads < 3 mA RMS of fault current.

c. Power off and then power on the system to reset any possible trips by the system.

d. Slowly increase the fault current until the AFE3010 SCR driver is pulsed and trips the solenoid. Note the

ammeter reading once the system trips.

e. If the system trips too early (< 4.5 mA RMS), then disconnect the system from power and decrease R7.

f.

If the system trips too late (> 5.5 mA RMS), then disconnect the system from power and increase R7.

4. Tune the system's Neutral-to-ground (N-G) detection.

a. Set up the system according to Figure 16. Note that this initial design process does not require testing N-

G detection with H-G fault or load currents.