UM1524 datasheet(13/35 Pages) STMICROELECTRONICS

13 / 35 page

UM1524

Hardware details

Doc ID 022901 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 the 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 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.

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

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.

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