Presents a precise calculation procedure to correctly set the necessary parameters when using a 3.3 V power supply.
This document provides a precise calculation process for setting necessary parameters when driving ACS™/TRIAC switches with a 3.3 V power supply, which is common in modern MCU-based home appliance applications. It focuses primarily on Q2 and Q3 operation modes but also includes advice for Q1 and Q4 quadrants.
The note covers the selection of gate resistors by analyzing variations in gate current due to temperature, component accuracy, and environmental factors. It includes specific calculation examples for STM8S and STM32 microcontrollers to determine the appropriate resistor values under worst-case conditions.
| Minimum ambient temperature for calculation | 0 °C |
|---|---|
| Gate current multiplier at 0 °C | 1.3 - 1.5 times higher |
| Zener diode voltage stability at 5.1 V and 5.6 V | Best stability |
| Power supply accuracy at 5 V | +10% |
| Zener diode stability variation at 3.3 V and 3.9 V | +0.6 V (420%) |
| Maximum gate current for STM8S HS pin at 3.3 V | 12 mA |
The minimum ambient temperature is set to 0 °C for most home appliance applications.
The gate current level is usually increased to a range 1.3 - 1.5 times higher at 0 °C.
The stability of the Zener voltage is best at 5.1 V and 5.6 V.
The maximum current capability is 12 mA as specified in the datasheet.