ADE7763_15 Datasheet, PDF (17/56 Pages) Analog Devices – Single-Phase Active and Apparent Energy Metering IC

Data Sheet
every 128/CLKIN seconds. The register is reset to its user-
programmed, full-scale value when a zero crossing on Channel 2
is detected. The default power-on value in this register is 0xFFF.
If the internal register decrements to 0 before a zero crossing is
detected and the DISSAG bit in the mode register is Logic 0, the
SAG pin goes active low. The absence of a zero crossing is also
indicated on the IRQ pin if the ZXTO enable bit in the interrupt
enable register is set to Logic 1. Irrespective of the enable bit
setting, the ZXTO flag in the interrupt status register is always
set when the internal ZXTOUT register is decremented to 0—
see the Interrupts section.
The ZXOUT register, Address 0x1D, can be written to and read
from by the user—see the Serial Interface section. The
resolution of the register is 128/CLKIN seconds per LSB;
therefore, the maximum delay for an interrupt is 0.15 seconds
(128/CLKIN × 2¹²).
Figure 33 shows the zero-crossing timeout detection when the
line voltage stays at a fixed dc level for more than CLKIN/128 ×
ZXTOUT seconds.
12-BIT INTERNAL
REGISTER VALUE
ZXTOUT
CHANNEL 2
ZXTO
DETECTION
BIT
Figure 33. Zero-Crossing Timeout Detection
ADE7763
PERIOD MEASUREMENT
The ADE7763 provides the period measurement of the line.
The PERIOD register is an unsigned, 16-bit register that is
updated every period and always has an MSB of zero.
The formula for the period register is shown below:
CLKIN 16
PERIOD 
4  32  f
Where CLKIN is the crystal frequency (3.579545 MHz
recommended), and f is the line frequency.
When CLKIN = 3.579545 MHz, the resolution of this register is
2.2 μs/LSB, which represents 0.013% when the line frequency is
60 Hz. When the line frequency is 60 Hz, the value of the
period register is approximately 7457d. The length of the register
enables the measurement of line frequencies as low as 13.9 Hz.
The period register is stable at ±1 LSB when the line is established
and the measurement does not change. This filter is associated
with a settling time of 1.8 seconds before the measurement is
stable. See the Calibrating an Energy Meter section for more on
the period register.
POWER SUPPLY MONITOR
The ADE7763 contains an on-chip power supply monitor. The
analog supply (AVDD) is continuously monitored. If the supply
is less than 4 V ± 5%, the ADE7763 will go into an inactive state
and no energy will accumulate. This is useful to ensure correct
device operation during power-up and power-down stages. In
addition, built-in hysteresis and filtering help prevent false
triggering due to noisy supplies.
AV_DD
5V
4V
0V
ADE7763
POWER-ON
INACTIVE ^INACTIVE
STATE
TIME
ACTIVE
INACTIVE
SAG
Figure 34. On-Chip Power Supply Monitor
As seen in Figure 34, the trigger level is nominally set at 4 V.
The tolerance on this trigger level is about ±5%. The SAG pin
can also be used as a power supply monitor input to the MCU.
The SAG pin goes logic low when the ADE7763 is in its inactive
state. The power supply and decoupling for the part should be
such that the ripple at AVDD does not exceed 5 V ± 5%, as
specified for normal operation.
Rev. C | Page 17 of 56