Datasheet

MAX71020
Single-Chip Electricity Meter AFE
30Maxim Integrated
one second. Additionally, the hardware does not permit
output values to fold back upon overflow.
WSUM_X (register 0x084) and VARSUM_X (register
0x088) are the signed sum of Phase-A and Phase-B
Wh or VARh values according to the metering equation
implemented by the CE code. WxSUM_X (x = 0 or 1,
registers 0x085 and 0x086) is the watt-hour value accu-
mulated for phase x in the last accumulation interval and
can be computed based on the specified LSB value.
Instantaneous Energy Measurement Variables
I_SQSUM_X and V_SQSUM (see Table 14) are the sum
of the squared current and voltage samples acquired
during the last accumulation interval.
The RMS values can be computed by the host controller
from the squared current and voltage samples as follows:
I
RMS
ACC
üüüüüüüüü
I
N
××
=
Other
V
RMS
ACC
üüüüüüüüü
V
N
××
=
Other transfer variables include those available for
frequency and those reflecting the count of the zero-
crossings of the mains voltage. These transfer variables
are listed in Table 15.
MAINEDGE_X (register 0x083) reflects the number of
half-cycles accounted for in the last accumulated interval
for the voltage signal. MAINEDGE_X is useful for imple-
menting a real-time clock based on the input AC signal.
Pulse Generation
Table 16 describes the CE pulse generation parameters.
The combination of the CECONFIG:PULSE_SLOW and
CECONFIG:PULSE_FAST bits (register 0x020[0:1]) con-
trols the speed of the pulse generator. The default zero
values of these configuration bits maintain the original
pulse rate given by the Kh equation, described below.
WRATE (register 0x021) controls the number of pulses
that are generated per measured Wh and VARh. The
lower WRATE is, the slower the pulse rate for the mea-
sured energy quantity; or conversely, the greater the
measured energy per pulse. By default, the pulse gener-
ators take their input from the W0SUM_X (register 0x085)
and VAR0SUM_X (register 0x089) result registers.
Table 15. Other Transfer Variables
Table 14. CE Energy Measurement Variables
CE
ADDRESS
NAME DESCRIPTION CONFIGURATION
0x8C I0SQSUM_X
The sum of squared current samples from each element.
LSB
I
= 6.08040 x 10
-13
IMAX
2
A
2
h
When EQU = 1, I0SQSUM_X is based on IA and IB.
Figure 8
0x8D I1SQSUM_X
0x90 V0SQSUM_X
The sum of squared voltage samples from each element.
LSB
V
= 6.08040 x 10
-13
VMAX
2
V
2
h
0x91
†
V1SQSUM_X
CE
ADDRESS
NAME DESCRIPTION
0x82 FREQ_X Fundamental frequency:
0x83 MAINEDGE_X
The number of edge crossings of the selected voltage in the previous accumulation
interval. Edge crossings are either direction and are debounced.
-6
32
2520.6Hz
LSB 0.509 10
2
≡ ≈×