STPM11 datasheet(25/46 Pages) STMICROELECTRONICS

25 / 46 page

STPM11, STPM12, STPM13, STPM14

Theory of operation

Doc ID 13167 Rev 8

25/46

Due to the innovative and proprietary power calculation algorithm, the frequency signal is

not affected by any ripple at twice the line frequency. This feature strongly reduces the

calibration time of the meter.

7.14

Driving a stepper motor

The STPM1x is able to directly drive a stepper motor. An internal divider (mono-flop and

decoder) generates stepper driving signals MA and MB from signal AW. 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 - 7.13) 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 one 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.

Different settings for led signal

KMOT (2 Bits)

APL=0

APL=1

Pulses

P/64

P/128

P/32

P/256

Table 14.

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

Obsolete

Product(s)

- Obsolete

Product(s)

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