STPM01_11 Datasheet, PDF (29/60 Pages) STMicroelectronics – Programmable single phase energy metering IC with tamper detection

STPM01
Theory of operation
In a practical example where APL = 2, and the desired P is 64000 pulses/kWh (= 17.7
Hz*kW), we have:
K_AW = 7.63*10-6 Wh
This means that the reading of 0x00001 in the active energy register represents 7.63 µWh,
while 0xFFFFF represents 8 Wh.
8.15
Driving a stepper motor (standalone)
When used in standalone mode (APL = 2 or APL = 3), the STPM01 is able to directly drive a
stepper motor. From signal AW, a stepper driving signals MA and MB are generated by
means of internal divider, mono-flop and decoder. The MA and MB signals are brought to
the MOP and MON pins that are able to drive the stepper motor. Several kinds of selections
are possible for the driving signals according to the configuration bits LVS and KMOT.
The numbers of pulses per kWh (PM) in the MOP and MON outputs are linked with the
number of pulses of the LED P (see previous paragraph) pin with the following relationship:
Table 13. Configuration of MOP and MON pins
LVS (1 Bit)
KMOT (2 Bits)
0
0
0
1
0
2
0
3
1
0
1
1
1
2
1
3
Pulses length
31.25 ms
31.25 ms
31.25 ms
31.25 ms
156.25 ms
156.25 ms
156.25 ms
156.25 ms
PM
P/64
P/128
P/32
P/256
P/640
P/1280
P/320
P/2560
The mono-flop limits the length of the pulses according to the LVS bit value.
The decoder distributes the pulses to MA and MB alternatively, which means that each of
them has only a half of selected frequency.
Negative power is computed with its own sign, and the MOP and MON signals invert their
logic state in order to make the backward rotation direction of the motor. See the diagram
below.
Doc ID 10853 Rev 8
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