UM1524 Datasheet, PDF (13/35 Pages) STMicroelectronics – This document describes the functions

UM1524
Hardware details
5.3
5.3.1
5.3.2
5.3.3
Power supply section
Capacitive power supply is used to build 3.6 V for the metering IC and microcontroller
section.
Programmable voltage reference U5
U5 TL431AI (package TO-92) is used to regulate the 3.6 V supply.
Current sensor CT1
CT1 E4626-X002(2500 turns, series resistance: 41.7 Ω) is the sensor for the primary
current channel.
Shunt RS1
RS1 300 µΩ is the sensor for the secondary current channel.
5.4
5.4.1
Neutral missing power supply section
The neutral missing power supply section is operational in case of neutral missing tamper. In
case of a neutral missing tamper condition, neutral is disconnected from the energy meter.
Therefore, there is no voltage input and so no output would be generated by the main
capacitive power supply. However, in the case of load present, there would be a valid input
signal on the current channel so energy would be consumed. Since the voltage on the
neutral channel is zero, so is the power (P = V x I). In order to take account of energy
consumed in this case, the neutral missing power supply section provides voltage supply to
the STPM10 metering IC. A zero crossing signal of 50 Hz is provided to the VIP pin of the
STPM10, so the STPM10 now calculates the energy consumption at a nominal voltage level
of 230 V.
Current sensor CT2
CT2 is used to develop the power supply for the board using a diode full wave rectifier circuit
in neutral missing condition.
5.5
EEPROM U3 section
EEPROM M24C32-RMN6TP (package: SO8, 32 Kbit) is interfaced to the microcontroller
using an I²C bus. Cumulative energy, MD, average PF and tamper information for seven
consecutive months are logged as months in EEPROM. For more details about EEPROM
data logging, refer to Section 6.2: EEPROM data log.
5.6
LCD section
LCD J3 is the connector for external 18* 4 LCD glass.
LCD glass OPT6089A (operating voltage 3 V, duty 1/4, Bias 1/3) offers various energy meter
specific symbols.
LCD glass is driven by the microcontroller internal LCD driver.
Doc ID 022901 Rev 1
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