STPM01 datasheet(25/56 Pages) STMICROELECTRONICS

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STPM01

Theory of operation

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8.13

Resetting the STPM01

The STPM01 has no reset pin. The device is automatically reset by the POR circuit when

the VCC crosses the 2.5V value but it can be reset also through the SPI interface giving a

dedicated command (see SPI section for remote reset command details).

In case of reset caused by POR circuit all clocks and both DC buffers in the analog part are

kept off for about 30ms and all blocks of digital part, except for SPI interface, which is hold in

a reset state for about 125ms after a reset condition.

When the reset is performed through SPI no delayed turn on is generated.

Resetting the STPM01 causes all the functional modules of STPM01 to be cleared including

the OTP shadow latches (see paragraph 16 for OTP shadow latches description)

The reset through SPI (Remote reset request) will normally take place during production

testing or in an application of meter with some on-board microprocessor when some

malfunction of metering device will be detected.

8.14

Energy to frequency conversion (standalone)

When used in standalone mode the STPM01 provides energy to frequency conversion both

for calibration and energy readout purposes. In fact one convenient way to verify the meter

calibration is to provide a pulse train signal with 50% duty cycle whose frequency signal is

proportional to the active energy under steady load conditions. In this case the user will

choose a certain number of pulses on the LED pin that will corresponds to 1kWh. We will

name this value as P.

The Active Energy frequency-based signal is available in the LED pin when APL=2 or

APL=3.

If APL=2 the LED is driven from internal signal AW (Active Energy) whose frequency is

proportional to the active energy. The signal AW is taken from the 11th bit of the active

energy register, consequently a relationship between the LSB value of the Active energy

Figure 19.

Different oscillator circuits (a): STPM12/14 with quartz; (b) STPM11/13; (c) STPM12/14

with external source

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