STPM01 datasheet(26/56 Pages) STMICROELECTRONICS

26 / 56 page

Theory of operation

STPM01

26/56

kAW = 1000/(2

11•P) [Wh] Eq. 1

If APL=3 the LED pin provides Active Energy frequency-based signal dependent on the

value of the KMOT configuration bit according to the following table. In this case the pulses

will have a fixed width of 31.25 ms.

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.

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 8Wh.

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 12.

Different settings for led signal

KMOT (2 Bits)

APL=2

APL=3

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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