ade7566 Analog Devices, Inc., ade7566 Datasheet - Page 46

• Manufacturer Part Number: ade7566
• Description: Single-phase Energy Measurement Ic With 8052 Mcu, Rtc, And Lcd Driver
• Manufacturer: Analog Devices, Inc.

ADE7566/ADE7569
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 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 50 shows how the zero-crossing signal is generated.
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
register, ZXTOUT. This unsigned, 12-bit register is decremented
(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
V2
V
V
N
P
Figure 50. Zero-Crossing Detection on Voltage Channel
PGA2
×1, ×2, ×4,
×8, ×16
0.73
{GAIN [7:5]}
1.0
V2
REFERENCE
43.24° @ 60Hz
ADC 2
LPF1
f
MODE1[6]
–3dB
HPF
LPF1
= 63.7Hz
ZX
CROSS
ZERO
Rev. 0 | Page 46 of 136
ZX
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 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 (1/MCLK × 2
when MCLK = 4.096 MHz.
Figure 51 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 sec.
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
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 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 (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
register is 0d960. The frequency register is stable at ±4 LSB when
the line is established and the measurement does not change.
REGISTER VALUE
12-BIT INTERNAL
CHANNEL
VOLTAGE
ZXTOUT
FLAG
ZXTO
BIT
Figure 51. Zero-Crossing Timeout Detection
12
)