ADE7166 datasheet(53/144 Pages) AD

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ADE7566/ADE7569/ADE7166/ADE7169

Rev. A | Page 53 of 144

POWER QUALITY MEASUREMENTS

Zero-Crossing Detection

Each ADE7566/ADE7569/ADE7166/ADE7169 has a zero-

crossing detection circuit on the voltage channel. This zero

crossing is used to produce a zero-crossing internal 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 54 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

MODE 1[6]

43.24° @ 60Hz

1.0

0.73

LPF1

Figure 54. Zero-Crossing Detection on the 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 3 SFR (MIRQSTH, 0xDE). If the ZX bit in the

Interrupt Enable 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 seconds. 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 3 SFR

(MIRQSTH, 0xDE), and the ZXTO bit in the Interrupt Enable 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 to or read by the

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

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

the maximum delay for an interrupt is 0.16 seconds (1/MCLK ×

212) when MCLK = 4.096 MHz.

Figure 55 shows the mechanism of the zero-crossing timeout

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

than MCLK/160 × ZXTOUT seconds.

12-BIT INTERNAL

ZXTOUT

ZXTO

FLAG

BIT

VOLTAGE

CHANNEL

Figure 55. Zero-Crossing Timeout Detection

Period or Frequency Measurements

The ADE7566/ADE7569/ADE7166/ADE7169 provide the

period or frequency measurement of the line. The period or

frequency measurement is selected by clearing or setting the

FREQSEL bit in the MODE2 register (0x0C). The period/

frequency register, PER_FREQ Register (0x0A), is an unsigned

16-bit register that is updated every period. If LPF1 is enabled, a

settling time of 1.8 seconds is associated with this filter before

the measurement is stable.

When the period measurement is selected, the measurement has a

2.44 μs/LSB (4.096 MHz/10), which represents 0.014% when the

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

of the period register is approximately 0d6827. The length of

the register 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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