71M6511 Datasheet, PDF (53/95 Pages) Teridian Semiconductor Corporation – Single-Phase Energy Meter IC

71M6511/71M6511H
Single-Phase Energy Meter IC
DATA SHEET
AUGUST 2007
Accumulation Interval m
Accumulation Interval m+1
Accumulation Interval m+2
MUX MUX MUX
cycle 1 cycle 2 cycle 3
MUX MUX
cycle n cycle 1
MUX MUX
cycle n cycle 1
Chop Polarity
Positive
Re-
versed
Positive
CE_BUSY interrupt
(falling edge)
Re- _Positive Re- _Positive
versed
versed
Re-
versed
Positive
Re-
versed
Positive
XFER_BUSY interrupt
(falling edge)
Figure 21: Chop Polarity w/ Automatic Chopping
If temperature compensation or accurate reading of the die temperature is required, alternate multiplexer cycles have to be
inserted in between the regular cycles. This is done under MPU firmware control by asserting the MUX_ALT bit whenever
necessary. Since die temperature usually changes very slowly, alternate multiplexer cycles have to be inserted very
infrequently. Usually, an alternate multiplexer cycle is inserted once for every accumulation period, i.e. after each XFER_BUSY
interrupt. This sequence is shown in Figure 22.
Accumulation Interval m
Accumulation Interval m+1
Accumulation Interval m+2
alt. MUX MUX MUX
cycle cycle 2 cycle 3
MUX alt. MUX
cycle n cycle
MUX alt. MUX
cycle n cycle
Chop Polarity
Positive
Re-
versed
Positive
Re-
versed
Positive
Re-
versed
Positive
Re-
versed
Positive
Re-
versed
Positive
CE_BUSY interrupt
XFER_BUSY interrupt
MUX_ALT
Figure 22: Sequence with Alternate Multiplexer Cycles
This sequence has the disadvantage that the alternate multiplexer cycle is always operated with positive connection.
Consequently, DC offset will appear on the temperature measurement, which will decrease the accuracy of this measurement
and thus cause temperature reading and compensation to be less accurate.
The sequence shown in Figure 23 uses the CHOP_EN bits to control the chopper polarity after each XFER_BUSY interrupt.
CHOP_EN is controlled to alternate between 10 (positive) and 01 (reversed) for the first multiplexer cycle following each
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