ADE7569 datasheet(59/144 Pages) AD

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ADE7566/ADE7569/ADE7166/ADE7169

Rev. A | Page 59 of 144

Active Power Gain Calibration

Active Power Sign Detection

Figure 65 shows the signal processing chain for the active power

calculation in the ADE7566/ADE7569/ADE7166/ADE7169. As

explained previously, the active power is calculated by filtering

the output of the multiplier with a low-pass filter. Note that

when reading the waveform samples from the output of LPF2,

the gain of the active energy can be adjusted by using the

multiplier and watt gain register (WGAIN[11:0]). The gain is

adjusted by writing a twos complement 12-bit word to the watt

gain register. Equation 12 shows how the gain adjustment is

related to the contents of the watt gain register.

The ADE7566/ADE7569/ADE7166/ADE7169 detect a change

of sign in the active power. The APSIGN flag in the Interrupt

Status 1 SFR (MIRQSTL, 0xDC) records when a change of sign

has occurred according to Bit APSIGN in the ACCMODE

1 SFR (MIRQENL, 0xD9), the 8052 core has a pending ADE

interrupt. The ADE interrupt stays active until the APSIGN

status bit is cleared (see the Energy Measurement Interrupts

section).

When APSIGN in the ACCMODE register (0x0F) is cleared

(default), the APSIGN flag in the Interrupt Status 1 SFR

(MIRQSTL, 0xDC) is set when a transition from positive–to-

negative active power has occurred.

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⎭

⎬

⎫

⎩

⎨

⎧ +

WGAIN

Power

Active

WGAIN

Output

(12)

For example, when 0x7FF is written to the watt gain register, the

power output is scaled up by 50% (0x7FF = 2047d, 2047/212 = 0.5).

Similarly, 0x800 = −2048d (signed, twos complement) and

power output is scaled by –50%. Each LSB scales the power

output by 0.0244%. The minimum output range is given when

the watt gain register contents are equal to 0x800 and the

maximum range is given by writing 0x7FF to the watt gain

energy) calculation in the ADE7566/ADE7569/ADE7166/

ADE7169.

When APSIGN in the ACCMODE register (0x0F) is set, the

APSIGN flag in the MIRQSTL SFR is set when a transition

from negative to positive active power occurrs.

Active Power No-Load Detection

The ADE7566/ADE7569/ADE7166/ADE7169 include a no-

load threshold feature on the active energy that eliminates any

creep effects in the meter. The part accomplishes this by not

accumulating energy if the multiplier output is below the no-

load threshold. When the active power is below the no-load

threshold, the APNOLOAD flag in the Interrupt Status 1 SFR

(MIRQSTL, 0xDC) is set. If the APNOLOAD bit is set in the

Interrupt Enable 1 SFR (MIRQENL, 0xD9), the 8052 core has a

pending ADE interrupt. The ADE interrupt stays active until

the APNOLOAD status bit is cleared (see the

Active Power Offset Calibration

The ADE7566/ADE7569/ADE7166/ADE7169 also incorporate

an active power offset register (WATTOS[15:0]). It is a signed,

twos complement, 16-bit register that can be used to remove

offsets in the active power calculation (see

Energy

Measurement Interrupts

Figure 63). An offset

can exist in the power calculation due to crosstalk between

channels on the PCB or in the IC itself. The offset calibration

allows the contents of the active power register to be maintained

at 0 when no power is being consumed.

section).

The no-load threshold level is selectable by setting the

APNOLOAD bits in the NLMODE register (0x0E). Setting

these bits to 0b00 disables the no-load detection, and setting

them to 0b01, 0b10, or 0b11 sets the no-load detection

threshold to 0.015%, 0.0075%, or 0.0037% of the multiplier’s

full-scale output frequency, respectively. The IEC 62053-21

specification states that the meter must start up with a load

equal to or less than 0.4% IPB, which translates to .0167% of the

full-scale output frequency of the multiplier.

The 256 LSBs (WATTOS = 0x0100) written to the active power

offset register are equivalent to 1 LSB in the waveform sample

0xCCCCD (838,861d) when inputs on the voltage and current

channels are both at full scale. At −60 dB down on the current

channel (1/1000 of the current channel full-scale input), the

average word value output from LPF2 is 838.861 (838,861/1,000).

One LSB in the LPF2 output has a measurement error of

1/838.861 × 100% = 0.119% of the average value. The active

power offset register has a resolution equal to 1/256 LSB of the

waveform register. Therefore, the power offset correction

resolution is 0.000464%/LSB (0.119%/256) at −60 dB.

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