Datasheet

Data Sheet ADE7758
Rev. E | Page 37 of 72
Similar to reactive power, the fastest integration time occurs
when the VAR gain registers are set to maximum full scale,
that is, 0x7FF. The time it takes before overflow can be scaled
by writing to the VARDIV register; and, therefore, it can be
increased by a maximum factor of 255.
By setting the REHF bit (Bit 1) of the interrupt mask register,
the ADE7758 can be configured to issue an interrupt (
IRQ
)
when Bit 14 of any one of the three VAR-hr accumulation
registers has changed, indicating that the accumulation register
is half full (positive or negative).
When overflow occurs, the VAR-hr accumulation registers
content can rollover to full-scale negative (0x8000) and continue
increasing in value when the reactive power is positive. Con-
versely, if the reactive power is negative, the VAR-hr accumulation
registers content can roll over to full-scale positive (0x7FFF)
and continue decreasing in value.
Setting the RSTREAD bit (Bit 6) of the LCYMODE register
enables a read-with-reset for the VAR-hr accumulation
registers; that is, the registers are reset to 0 after a read
operation.
VARG[11:0]
VARDIV[7:0]
90° PHASE
SHIFTING FILTER
MULTIPLIER
I
V
HPF
CURRENT SIGNAL–i(t)
0x2851EC
0x00
0xD7AE14
VOLTAGE SIGNAL–v(t)
0x2852
0x00
0xD7AE
+
+
+
+
LPF2
%
SIGN 2
6
2
0
2
–1
2
–2
2
–3
2
–4
V
AR
OS[11:0]
VARHR[15:0]
15 0
40 0
TOTAL REACTIVE POWER IS
ACCUMULATED (INTEGRATED) IN
THE VAR-HR ACCUMULATION REGISTERS
π
2
PHCAL[6:0]
Φ
04443-072
Figure 73. ADE7758 Reactive Energy Accumulation