AN2799

Hardware

5/14

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Up to 3 USARTs (ISO 7816 interface, LIN, IrDA capability, modem control)

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Up to 2 SPIs (18 Mbit/s)

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CAN interface (2.0B Active)

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USB 2.0 full speed interface

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2.1.1

STPM01

The STPM01 is a programmable single-phase energy metering IC which is designed for

effective measurement of active, reactive and apparent energy in a power line system using

a Rogowski coil, a current transformer and shunt sensors. The solution presented in this

document is based on a current transformer sensor. The following list is a brief description of

the main features of the STPM01. For more details, please refer to the device datasheet.

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Active, reactive, apparent energies and RMS values

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Ripple-free active energy pulsed output

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Live and neutral monitoring for tamper detection

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Easy and fast digital calibration in only one point over the whole current range

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OTP for calibration and configuration

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Selectable RC or crystal oscillator

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Supports 50-60 Hz - IEC62052-11, IEC62053-2X specification

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Less than 0.1% error

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Precision voltage reference: 1.23 V and 30 ppm/°C max

2.2

Hardware description

The hardware used in managing the STPM01 by the STM32x microcontroller is described in

this section.

Figure 2 shows a reference schematic to interface the STM32x microcontroller

with the STPM01. The STPM01 bidirectional data line is connected to the SPI-MISO of the

STM32. This is because the speeds for the data read and data write operations of the

STPM01 SPI interface are much too different: 32 MHz for the read operation and 100 kHz

for the write operation. In fact during the write operation, the serial communication is

emulated by software to have very slow communication on the STPM01 data line and during

the read operation, the STM32 SPI peripheral is used to reach the maximum speed

possible. Since the maximum speed of the STM32 SPI is 18 MHz, it doesn't matter which

SPI peripheral is used to have the maximum read bit rate. In this application the SPI2 is

used. The STPM01 clock is provided by the PA8 pin configured as the MCO alternate

function. The AC current is provided to the STPM01 by a current transformer connected to

the current channel 1. For more details about analog parts related to the STPM01, please

refer to the STPM01 datasheet.

Note:

The solution has been validated using the “SmartPlug” board. For further details please

refer to the “SmartPlug hardware user manual” .