SA9904B Datasheet, PDF (7/12 Pages) List of Unclassifed Manufacturers – Three Phase Power / Energy IC with SPI Interface

SA9904B
sames
REGISTER DESCRIPTION
Active and reactive registers
The active and reactive power is accumulated in 24 bit registers
for each phase. These registers are 24 bit up/down counters,
that increment or decrement at a rate of 320k samples per
second at rated conditions.
23 22 21 20 19 10 9 8 7 6 5 4 3 2 1 0
Active or Reactive Energy Register
The register values will increment for positive energy flow and
decrement for negative energy flow as indicated in figure 10.
Register wrap around
Positive energy flow
Register values
0
H7FFFFF
................ _(8388607)
H800000
(8388608)
................
HFFFFFF
(16777215)
Negative energy flow
DR-01590
Register wrap around
Figure 10: Register increment / decrement showing the
register wrap around
The active and reactive registers are not reset after access, so
in order to determine the correct register value, the previous
value read must be subtracted from the current reading. The
data read from the registers represents the active or reactive
power integrated over time. The increase or decrease between
readings represent the measured energy consumption. At rated
conditions, the active and reactive registers will wrap around
every 52 seconds. The micro controller program needs to take
this condition into account when calculating the difference
between register values.
As an example lets assume that with a constant load connected,
the delta value (delta value = present register - previous register
value) is 22260. Because of the constant load, the delta value
should always be 22260 every time the register is read and the
previous value subtracted (assuming the same time period
between reads). However this will not be true when a wrap
around occurs, as the following example will demonstrate:
Description
Variable Decimal
Hex
Present register value new_val 16767215 0x00FFD8EF
Previous register value old_val 16744955 0x00FF81FB
new_val - old_val = delta_val 22260 0x000056F4
The register now wraps around so after the next read
the values are as follows:
Present register value new_val
12259 0x00002FE4
Previous register value old_val 16767215 _0x00FFD8EF
new_val - old_val = delta_val -16754956 _0x00FFA90B
Using this delta value will result in incorrect calculations.
Voltage registers
The three voltage registers contain the RMS voltage measured
for each phase.
The RMS voltage measurement is accurate to 1% for a range
of 50% to 115% of the rated mains voltage.
23 22 21 20 19 10 9 8 7 6 5 4 3 2 1 0
Voltage Register
Frequency register
The single frequency register contains the measured mains
frequency information for a valid phase. Internal logic ensures
that the frequency information is generated from the same
phase being used for the F50 output. Only bits D0 to D9 are
used for the frequency calculation however the remaining bits
must still be clocked out as additional information can be
derived from these data bits.
Frequency Register
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Mains Frequency
Not used
Missing phase
Phase sequence
error
Voltage zero
crossover
Bit location Description
0 to 9
These bits represent a value that is used
in the frequency calculation
10 to 17
18,19,20
Not used
Missing phase. These bits indicate which
phase is missing during a lost phase
condition.
D18 D19 D20 Missing phase
1 X X Phase 1
X 1 X Phase 2
X X 1 Phase 3
21,22
The phase error status can be ascertained
from these two bits.
D21 D22 Missing phase
0 0 No phase error
0 1 Phase sequence error.
1 X Missing phase
23
Voltage zero crossover. This bit changes
state with the rising edge of the mains
voltage.
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