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ADE7762
(Rev.:Rev0)

Polyphase Energy Metering IC with Phase Drop Indication

Analog Devices 

ADE7762

PHASE MONITOR

The ADE7762 has phase monitoring functions to detect phase

dropout, phase sequence error, and reverse polarity using four

pins. Phase dropout has the highest priority, and reverse

polarity has the lowest priority. If a phase dropout occurs, phase

sequence error indication is disabled until all three phases are

above the phase dropout level (see the Phase Dropout Error

section). Because the dropout detection level is not set to zero, a

phase can have some small voltage during a phase dropout

condition. Therefore, reverse polarity is still indicated on that

phase if the proper conditions occur.

The phase monitor circuit functions by multiplexing signals onto

the four pins. The four multiplexed pins are LED_CTRL, LED_A,

LED_B, and LED_C. Two LEDs can be connected to each pin as

shown in Figure 21. When LED_CTRL is high, LED_A is low to

turn on an LED and indicate a phase drop condition on Phase A.

When LED_CTRL is low, LED_A is high to indicate a reverse

polarity (REVP) condition on Phase A. Phase sequence error is

indicated by blinking the Phase Seq/Drop LEDs.

LED_CTRL switches at a rate of 131 kHz so that both the Phase

Seq/Drop LEDs and REVP LEDs can appear to be on simultane-

ously, which allows indication of phase dropout and REVP at the

same time. For the timing diagram, see Figure 3.

PHASE

SEQ/DROP

LED_CTRL

PHASE

SEQ/DROP

PHASE

SEQ/DROP

REVP

REVP

RLOAD

REVP

RLOAD

RLOAD

Figure 21. Phase Monitor Circuit

LED_A

LED_B

LED_C

PHASE DROPOUT ERROR

The ADE7762 indicates a phase drop condition when there is a

low voltage signal or no voltage signal on a phase. The phase

dropout condition occurs when the amplitude of the phase

drops below 20% of full-scale analog input voltage or when a

zero crossing is not followed by another zero crossing on that

phase for 150 ms. When this occurs, a phase dropout signal is

generated, and the Phase Seq/Drop LED is turned on for the

missing phase. The delay between the phase drop condition

occurring at the analog inputs and indication of the condition

on the LED outputs is approximately 150 ms. During a phase

dropout condition, energy continues to accumulate on the

dropped channel, as well as the other channels, and phase

sequence error indication is disabled. The Phase Seq/Drop LED

for the dropped phase is turned off when the zero crossings

return for more than 150 ms and there is more than 20% of full-

scale input voltage on the voltage input of that phase.

PHASE SEQUENCE ERROR

The ADE7762 detects the zero crossing of each phase. A phase

sequence error occurs when the sequence A>B>C>A> … is

violated. If a phase sequence error occurs, the Phase Seq/Drop

LEDs blink at 1 Hz (see Figure 22).

Phase sequence error and REVP can be displayed simultane-

ously. The REVP LEDs continue to indicate reverse polarity if

the proper conditions exist. For example, if the phase sequence

becomes A>C>B>A… and Phase B has negative active energy

accumulated, then the REVP LED for Phase B is on solid, and

all of the Phase Seq/Drop LEDs are blinking at 1 Hz. The delay

in indicating the phase sequence error with blinking LEDs is

approximately 150 ms from the time that a phase sequence

error occurs.

PHASE REVERSE POLARITY DETECTION

When reverse power is detected on any phase, the correspond-

ing REVP LED turns on for that phase. For example, if the

power for Phase A is negative, the REVP LED connected to

LED_A turns on. The indication of REVP on the LED_A,

LED_B, or LED_C pins is nearly instantaneous. As soon as the

input to the ADCs changes and the power is calculated such

that there is a reverse power condition on any phase, the

appropriate LED is turned on.

Rev. 0 | Page 18 of 28

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