ADE7762 datasheet(19/28 Pages) AD

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Preliminary Technical Data

ADE7762

Rev. PrB | Page 19 of 28

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 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 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 25. When LED_CTRL is high, LED_A would be

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.

RLOAD

REVP

LED_A

PHASE

SEQ/DROP

LED_CTRL

RLOAD

REVP

LED_B

PHASE

SEQ/DROP

RLOAD

REVP

LED_C

PHASE

SEQ/DROP

Figure 25. Phase Monitor Circuit

Phase Dropout Error

The ADE7762 indicates a phase drop condition when there is

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 vio-

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

blink at 1 Hz (see Figure 26).

Phase sequence error and REVP can be displayed simultaneously.

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 would be 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 SEQ/DROP LEDS ARE OFF.

A = 0

B = –120

C = +120

PHASE SEQ/DROP LEDS ARE BLINKING AT 1Hz.

A = 0

C = –120

B = +120

VOLTAGE

WAVEFORMS

80% FS

RISING EDGE

ZERO

CROSSINGS

VOLTAGE

WAVEFORMS

RISING EDGE

ZERO

CROSSINGS

80% FS

PHASE SEQ/DROP LED FOR PHASE B IS ON.

A = 0

C = –120

B = +120

RISING EDGE

ZERO

CROSSINGS

VOLTAGE

WAVEFORMS

80% FS

20% FS

Figure 26. Phase Sequence Detection

Reverse Polarity Error

When reverse power is detected on any phase, the

corresponding 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.

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