STPM11 datasheet(23/43 Pages) STMICROELECTRONICS

23 / 43 page

STPM11/12/13/14

Theory of operation

23/43

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.

In case of detected negative power the behavior of MOP and MON depends on the ABS

configuration bit status. If this bit is set, the negative power is computed as it was positive

(absolute value), and the MOP and MON signals maintain the pulse sequence in order to

keep the forward rotation direction of the motor. If ABS is zero, 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 12.

Different settings for led signal

KMOT (2 Bits)

APL=0

APL=1

Pulses

P/64

P/128

P/32

P/256

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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