July 2014

DocID15255 Rev 2

1/29

29

AN2859

Application note

Multiplexed diagnostics of AC switches

using two STCC08

Introduction

The aim of this application note is to present opportunities to reduce the number of input

pins used on a microcontroller unit (MCU) to diagnose failures of several AC switches with

the STCC08. This document deals with the multiplexed diagnostics of two STCC08 and

gives technical recommendations on the implementation of this solution.

STCC08 overview

The STCC08 has been designed to improve home appliance safety. This new device can

back to the microcontroller unit a signal image of the voltage across the controlled AC

switch (this signal defines the AC switch state). The STCC08 has three functional blocks

(see Figure 1).

• A "gate driver" block used to drive an AC switch and to interface directly the STCC08 with

the MCU (CMOS compatible)

• A "power switch signal shaping" block used to measure the AC switch voltage in both AC

line cycles

• An "AVF driver" block used to give an image of the AC switch voltage to the MCU (digital

information)

Figure 1. STCC08 block diagram

For more information about the STCC08, please refer to the ST Application note AN2716.

AVF

VCC

GND

RIG

AC

IN

G

Power switch

signal shaping

AVF driver

Gate driver

+

-

AVF

GND

STCC08

STCC08

AC

RIG

G

AVF

IN

GND

VCC

N/C

SO -8

1

2

3

4

8

5

6

7

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