MAX78615-LMU Datasheet, PDF (28/63 Pages) Maxim Integrated Products – Digital Temperature Compensation

MAX78615+LMU Data Sheet
Power Calculations
This section describes the detailed flow of power calculations in the MAX78615+LMU. Generic equations for AC
power measurement are listed in the table below.
Register
PA
PB
PQA
PQB
WATT_A
WATT_B
WATT_C
VAR_A
VAR_B
VAR_C
VA_A
VA_B
VA_C
PFA
PFB
PFC
Description
Instantaneous Active Power
Instantaneous Reactive Power
Average Active Power (P)
Average Reactive Power (Q)
Apparent Power (S)
Power Factor
Time Scale
1 sample
1 interval
NOTE: WATT_C, VAR_C and VA_C outputs are always scaled by a factor of 0.5.
Active Power (P)
The instantaneous power results (PA, PB) are obtained by multiplying aligned instantaneous voltage and current
samples. The sum of these results are then averaged over N samples (accumulation time) to compute the average
active power (WATT_A, WATT_B), and the aggregate average power (WATT_C).
VA
X
PA
IA
N-1
PA_SUM
∑
N
x
If
|x|< |y|
z=0
z
n=0
WATT_A
y
PA_OFFS
+
WATT_C
VB
X
PB
IB
N-1
PB_SUM
∑
N
n=0
x
If
|x|< |y|
z=0
z
y
WATT_B
PB_OFFS
Figure 17. Active Power Measurement
The value in the Px_OFFS register is the “Power Offset” for the power calculations. Full scale values in the Px_OFFS
register are subtracted from the magnitude of the averaged active power. If the resulting active power value
results in a sign change, zero watts are reported.
Rev 2
28