UM1529 datasheet(13/35 Pages) STMICROELECTRONICS

13 / 35 page

UM1529

Hardware details

Doc ID 022953 Rev 1

13/35

5.3

Power supply section

Capacitive power supply is used to build 3.6 V for the metering IC and microcontroller

section.

5.3.1

Programmable voltage reference U5

U5 TL431AI (package TO-92) is used to regulate the 3.6 V supply.

5.3.2

Current sensor CT1

CT1 E4626-X002 (2500 turns, series resistance: 41.7

Ω) is the sensor for primary current

channel.

5.3.3

Shunt RS1

RS1 300 µ

Ω is the sensor for the secondary current channel.

5.4

Neutral missing power supply section

The neutral missing power supply section is operational in the case of neutral missing

tamper. In the case of neutral missing tamper condition, neutral is disconnected from the

energy meter. Hence, there is no voltage input and therefore 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 it now calculates the energy consumption at a nominal voltage level of 230 V.

5.4.1

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

Dual interface EEPROM M24LR64-RMN6T/2 (package: SO8, 64 Kbit) is interfaced to the

microcontroller using the I2C bus. This is a dual interface EEPROM and we can

communicate with this device using I2C communication (wired) as well as RF interface

(wireless) using an RF reader. 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.

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