STPM01FTR datasheet(29/60 Pages) STMICROELECTRONICS

29 / 60 page

STPM01

Theory of operation

Doc ID 10853 Rev 8

29/60

In a practical example where APL = 2, and the desired P is 64000 pulses/kWh (= 17.7

Hz*kW), we have:

KAW = 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:

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.

Table 13.

Configuration of MOP and MON pins

LVS (1 Bit)

KMOT (2 Bits)

Pulses length

31.25 ms

P/64

31.25 ms

P/128

31.25 ms

P/32

31.25 ms

P/256

156.25 ms

P/640

156.25 ms

P/1280

156.25 ms

P/320

156.25 ms

P/2560

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