STPMC1 datasheet(34/77 Pages) STMICROELECTRONICS

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Theory of operation

STPMC1

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Doc ID 15728 Rev 6

Example 10: energy registers LSB value for SYS = 0, 1, 2, 4, 5, 6, 7

C = 64000 pulses/kWh = 17.7 Hz*kW

KP = KF = 15.258 *10-6 Wh

KQ = KR = 15.258 *10-6 VArh

This means that the reading of 0x00001 in the active energy register represents 15.258

µWh, while 0xFFFFF represents 16 Wh.

Example 11: Energy registers LSB value for SYS = 3

C = 64000 pulses/kWh = 17.7 Hz*kW

KP = 15.258 *10-6 Wh

KF = 30.517 *10-6 Wh

KQ = KR = 30.517 *10-6 VArh

From 3-phase active energy wide band signal the stepper driving signals

MA and MB

(output from MOP and MON pins) are generated. The frequency of these signals can be

configured as shown in paragraph

9.13.

9.12

Using STPMC1 in microcontroller based meter - peripheral

operating mode (configuration bits: APL, KMOT, LVS, FUND)

The higher flexibility of the STPMC1 allows its use in microcontroller based energy meters.

In this case the STPMC1 must be programmed to work in peripheral mode setting bit APL

[1] = 0. All the SPI pins (SCS, SCLNCL, SDATD, SYN) are used only for communication

purposes, allowing the microcontroller to write and read the internal STPMC1 registers.

The peripheral mode has two further different configuration modes according to the status of

the APL configuration bit, which changes the function of MOP, MON and LED pins as

described below.

APL = 0:

In the MOP pin, the

ZCR signal is available (see paragraph 9.5 for details on ZCR signal);

The pin MON provides the WatchDOG signal. The DOG signal generates a 16 ms long

positive pulse every 1.6 seconds. Generation of these pulses can be suspended if data are

read in intervals shorter than 1.6 ms. The DOG signal is actually a watchdog reset signal

that can be used to control an operation of an on-board microcontroller. It is set to high

whenever the VCC voltage is below 2.5 V, but after VCC goes above 2.5 V this signal starts to

run.

It is expected that an application microcontroller should access the data in the metering

device on regular basis, at least 1/s (recommended is 32/s). Every latching of results in the

metering device requested from the microcontroller also resets the watchdog. If latching

requests does not follow each other within 1.6 second, an active high pulse on MON is

produced, because device assumes that microcontroller does not operate properly. This

signal can be either control the RESET pin of the microcontroller or it can be tied to some

interrupt pin. The second chance is recommended for a battery backup application which

can enter some sleep mode due to power down condition and should not be reset by

metering device.

The LED pin can be configured through LVS, FUND and KMOT to output different energy

signals, as shown in the table below.

STPMC1 数据表(PDF) 34 Page - STMicroelectronics

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