ADE7569 datasheet(46/136 Pages) AD

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ADE7566/ADE7569

Preliminary Technical Data

Rev. PrA | Page 46 of 136

POWER QUALITY MEASUREMENTS

Zero-Crossing Detection

Each ADE7566/ADE7569 has a zero-crossing detection circuit

on the voltage channel. This zero crossing is used to produce an

external zero-crossing signal (ZX) and is used in calibration mode.

The zero-crossing is generated by default from the output of

LPF1. This filter has a low cut-off frequency and is intended for

50 Hz and 60 Hz systems. If needed, this filter can be disabled

to allow a higher frequency signal to be detected or to limit the

group delay of the detection. If the voltage input fundamental

frequency is below 60 Hz, and a time delay in ZX detection is

acceptable, it is recommended to enable LPF1. Enabling LPF1

limits the variability in the ZX detection by eliminating the high

frequency components.

Figure 42 shows how the zero-crossing signal is generated.

×1, ×2, ×4,

×8, ×16

ADC 2

REFERENCE

LPF1

f–3dB = 63.7Hz

PGA2

{GAIN [7:5]}

ZERO

CROSS

HPF

MODE1[6]

43.24° @ 60Hz

1.0

0.73

LPF1

Figure 42. Zero-Crossing Detection on Voltage Channel

The zero-crossing signal ZX is generated from the output of

LPF1 (bypassed or not). LPF1 has a single pole at 63.7 Hz (at

MCLK = 4.096 MHz). As a result, there is a phase lag between

the analog input signal V2 and the output of LPF1. The phase

lag response of LPF1 results in a time delay of approximately

2 ms (@ 60 Hz) between the zero crossing on the analog inputs

of the voltage channel and ZX detection.

The zero-crossing detection also drives the ZX flag in the

Interrupt Status Register 3 SFR (MIRQSTH, 0xDE). If the ZX

bit in the Interrupt Enable Register 3 SFR (MIRQENH, 0xDB)

is set, the 8052 core has a pending ADE interrupt.

The ADE interrupt stays active until the ZX status bit is cleared

(see the Energy Measurement Interrupts section).

Zero-Crossing Timeout

The zero-crossing detection also has an associated timeout

(1 LSB) every 160/MCLK sec. The register is reset to its user

programmed, full-scale value every time a zero crossing is

detected on the voltage channel. The default power-on value in

this register is 0xFFF. If the internal register decrements to 0

before a zero crossing is detected in the Interrupt Status

Interrupt Enable Register 3 SFR (MIRQENH, 0xDB) is set, the

8052 core has a pending ADE interrupt.

The ADE interrupt stays active until the ZXTO status bit is

cleared (see the Energy Measurement Interrupts section).

The ZXOUT register (Address 0x11) can be written or read by

the user (see the Energy Measurement Register List section).

The resolution of the register is 160/MCLK sec per LSB. Thus,

the maximum delay for an interrupt is 0.16 sec (128/MCLK × 212)

when MCLK = 4.096 MHz.

Figure 43 shows the mechanism of the zero-crossing timeout

detection when the line voltage stays at a fixed dc level for more

than CLKIN/160 × ZXTOUT sec.

12-BIT INTERNAL

ZXTOUT

ZXTO

FLAG

BIT

VOLTAGE

CHANNEL

Figure 43. Zero-Crossing Timeout Detection

Period or Frequency Measurements

The ADE7566/ADE7569 provide the period or frequency

measurement of the line. The period or frequency measurement

is selected by clearing or setting FREQSEL bit in the MODE2

every period. If LPF1 is enabled, a settling time of 1.8 sec is

associated with this filter before the measurement is stable.

When the period measurement is selected, the measurement

has a 2.44 μs/LSB (MCLK/10) when MCLK = 4.096 MHz,

which represents 0.014% when the line frequency is 60 Hz.

When the line frequency is 60 Hz, the value of the period

enables the measurement of line frequencies as low as 12.5 Hz.

The period register is stable at ±1 LSB when the line is

established and the measurement does not change.

When the frequency measurement is selected, the measurement

has a 0.0625 Hz/LSB resolution when MCLK = 4.096 MHz,

which represents 0.104% when the line frequency is 60 Hz.

When the line frequency is 60 Hz, the value of the frequency

the line is established and the measurement does not change.

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