ADE7752A datasheet(17/24 Pages) AD

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ADE7752/ADE7752A

Rev. C | Page 17 of 24

POWER SUPPLY MONITOR

The ADE7752 contains an on-chip power supply monitor. The

power supply (VDD) is continuously monitored by the ADE7752.

If the supply is less than 4 V ± 5%, the outputs of the ADE7752

are inactive. This is useful to ensure correct device startup at

power-up and power-down. The power supply monitor has

built-in hysteresis and filtering. This gives a high degree of

immunity to false triggering due to noisy supplies.

As can be seen from Figure 23, the trigger level is nominally set

at 4 V. The tolerance on this trigger level is about ±5%. The

power supply and decoupling for the part should be such that

the ripple at VDD does not exceed 5 V ± 5% as specified for

normal operation.

HPF AND OFFSET EFFECTS

Figure 25 shows the effect of offsets on the real power calcula-

tion. As can be seen, an offset on the current channel and

voltage channel contribute a dc component after multiplication.

Since this dc component is extracted by the LPF and is used to

generate the real power information for each phase, the offsets

contribute a constant error to the total real power calculation.

This problem is easily avoided by the HPF in the current

channels. By removing the offset from at least one channel, no

error component can be generated at dc by the multiplication.

Error terms at cos(ωt) are removed by the LPF and the digital-

to-frequency conversion. See the Digital-to-Frequency

Conversion section.

()

{}

()

{}

()

( )

()

cos

The HPFs in the current channels have an associated phase

response that is compensated for on-chip. Figure 24 and

Figure 26 show the phase error between channels with the

compensation network. The ADE7752 is phase compensated

up to 1 kHz as shown. This ensures correct active harmonic

power calculation even at low power factors.

VDD

INTERNAL

RESET

INACTIVE

TIME

ACTIVE

INACTIVE

VOS × IOS

IOS × V

VOS × I

DC COMPONENT (INCLUDING ERROR TERM)

IS EXTRACTED BY THE LPF FOR REAL

POWER CALCULATION

FREQUENCY – RAD/S

× I

Figure 23. On-Chip Power Supply Monitor

Figure 25. Effect of Channel Offset on the Real Power Calculation

FREQUENCY (Hz)

0.07

0.06

–0.01

1000

200

400

600

800

0.03

0.02

0.01

0.05

0.04

100

300

500

700

900

FREQUENCY (Hz)

0.010

0.008

–0.004

0.002

–0.002

0.006

0.004

Figure 24. Phase Error Between Channels (0 Hz to 1 kHz)

Figure 26. Phase Error Between Channels (40 Hz to 70 Hz)

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