ST AN2716 APPLICATION NOTE

STCC08 application guidelines

Introduction

The purpose of this document is to:

■ Describe the STCC08 device features

■ Give technical recommendations to:

– Implement the STCC08 in the appliance – Achieve robust STCC08 design regarding EMI tests (IEC 61000-4-4)

AN2716

June 2010 Doc ID 14460 Rev 2 1/28

www.st.com

Contents AN2716

1 STCC08 description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.1 Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2 STCC08 non-insulated and insulated application diagram . . . . . . . . . . . . 5

1.3 AC switch control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.4 AC switch failure mode detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.4.1 STCC08 AVF output configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.4.2 AC switch state detection principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.4.3 AC switch failures detection during normal operation . . . . . . . . . . . . . . . 9

1.5 AVF signal reading synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.5.1 Detection window width definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.5.2 AC switch state detection after IN signal removal . . . . . . . . . . . . . . . . . 13

2 STCC08 consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3 Recommended component values . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4 ZVS detection application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5 Electromagnetic compatibility (EMC) tests . . . . . . . . . . . . . . . . . . . . . 18

5.1 Demonstration board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5.2 IEC 61000-4-4 burst immunity test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5.2.1 Test conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5.2.2 Demonstration board immunity test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5.2.3 Advice to improve the application immunity . . . . . . . . . . . . . . . . . . . . . . 19

6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Appendix A Timing definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Appendix B Demonstration board component layout. . . . . . . . . . . . . . . . . . . . . 24

Appendix C Demonstration board schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

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AN2716 Contents

Appendix D Demonstration board circuit layout view. . . . . . . . . . . . . . . . . . . . . 26

Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Doc ID 14460 Rev 2 3/28

STCC08 description AN2716

1 STCC08 description

1.1 Main features

The STCC08 was designed to improve the safety of home appliances (see Reference 1.). This new device can drive up to 10 mA I Reference 2.) and send back to the microcontroller (MCU) a signal image of the voltage across the controlled AC switch. The STCC08 has three functional blocks (see Figure 1 and

Ta bl e 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

● An “AVF driver” block used to give an image of the AC switch voltage to the MCU

(digital information)

Figure 1. STCC08 block diagram

AC switches (TRIAC, ACST and ACS - see

G (6)

V (5)

AC (4)

Power switch

signal shaping

Table 1. STCC08 pin descriptions

Gate driver

STCC08

AVF driver

IN (1)

R (7)

AVF

AVF (2)

GND

GND (8)

AVF

N/C

SO-8 package

Pin Symbol Type Description

1 IN SIGNAL AC switch drive

2 AVF SIGNAL Alternating voltage feedback: AC switch state output

3 NC Not connected

4 AC SIGNAL AC switch state sense input

POWER Positive power supply

6 G SIGNAL AC switch gate driver output

7RIGSIGNAL AC switch gate current setting

8 GND POWER Power supply reference

GND

Knowing the STCC08 IN input state (used to turn on or off the AC switch) and the voltage across the controlled AC switch (given by the STCC08 AVF output signal state), the MCU is able to identify all AC switch failures (diode mode, short circuit, or open circuit) and to take the appropriate actions to put the appliance in a secure state (see Reference 3.) by switching off an appliance front-end relay (see Section 1.4.3).

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AN2716 STCC08 description

1.2 STCC08 non-insulated and insulated application diagram

The STCC08 is dedicated to applications with MCU. Figure 2 and Figure 3 show respectively the STCC08 non-insolated and insolated application diagrams. The STCC08 is compatible with 3.3 V and 5 V power supplies. The DC power supply must be a negative one. This means the V V

(3.3 V or 5 V) below neutral. Such a connection is mandatory to drive ACS and most

ACST and TRIAC devices (AC switches can be triggered only by a current taken from the gate).

Figure 2. Un-insulated application diagram

terminal has to be connected to neutral. The GND voltage is then

Neutral

ACS

RAC

Load

RShunt

Line

Front end relay

Power switch

signal shaping

STCC08

Figure 3. Insulated application diagram

Neutral

ACS

Gate driver

AVF driver

CC1

VCC= 3.3V to 5V

AVF

GND

Un- insulatated

5 V or 3.3 V

Power supply

MCU

Power supply

Insulated

CC2

Line

Load

RShunt

Front end relay

RAC

Power switch

signal shaping

STCC08

AVF driver

AVF

GND

OPTO1

CC1

AVF

OPTO2

CC2

MCU

Doc ID 14460 Rev 2 5/28

STCC08 description AN2716

1.3 AC switch control

The STCC08 controls up to 10 mA IGTTRIAC, ACST and ACS through the “gate driver” block designed to:

● Drive the AC switch according to the IN control input state (CMOS compatible)

– For IN = 1 = V

– For IN = 0 = GND Ö the AC switch is turned off

● Regulate the gate current of the AC switch thanks to the internal current controller

The gate current value (Pin G - to turn on the AC switch) is defined by the external resistor R

value (resistor connected between the STCC08 RIG input and ground). Figure 4 gives

the maximum value of this resistor (R temperature (T

amb_min

switch junction temperature increases when the AC switch is on (T current required to turn on the AC switch decreases (I ambient temperature has to be considered.

Ö the AC switch is turned on

) according to the minimum ambient

IG_max

) of the appliance for two AC switch IGT values. Note that as the AC

> T

< IGT). So only the minimum

), the IG gate

amb

Figure 4. Resistor R

AC switch I

130

120

110

100

-20-15-10-5 0 5 1015202530

value according to the minimum ambient temperature and

IG_max

For example, with a 10 mA I maximum 30 Ω R

resistor can be used to turn on the AC switch throughout the whole

appliance temperature range.

()Ω

IGTAC Switch:

IGT 10mA @ 25°C IGT 5mA @ 25 °C

amb_min

AC switch and a -20 °C minimum ambient temperature, a

(°C)

1.4 AC switch failure mode detection

1.4.1 STCC08 AVF output configuration

The STCC08 AVF driver block is used to send the AC switch state to the MCU (see

Section 1.4.2). The STCC08 AVF output is an open collector and can be loaded with an

external resistor (R

Figure 5).

6/28 Doc ID 14460 Rev 2

) or connected directly to the MCU, in pull-up input configuration (see

AVF

AN2716 STCC08 description

Figure 5. STCC08 AVF output configuration

PULL-UP

= 5.5 V,

STCC08

AVF driver

(a) AVF output loaded with an external resistor (R )

The I defines the minimal R the R

current in the STCC08 AVF pin must be lower than 5 mA (I

AVF

or R

AVF

PULL-UP

AVF

GND

MCU

or pull-up resistor value to use. For example, with V

AVF

resistor value must be higher than 1.1 kΩ to fulfill this condition.

STCC08

AVF driver

(b) AVF output loaded with the MCU pull-up resistor (R )

AVF

GND

AVF

AVF _max

MCU

). Equation 1

CC_max

Equation 1

maxCC

or R

(

maxAVF

PULL-UP

)

mA5

resistor values modify the AVF signal rise time

AVF

RorR

PULLminAVF

minUP

The AVF signal toggles from VCC to GND according to the AC switch state and the AC line (see Section 1.4.2). The R (t R

). This rise time increases with the MCU I/O pin capacitance and R

R_AVF

PULL-UP

resistors. To limit the influence of this delay on the AC switch state detection (see

AVF

Section 1.4.2) and on the ZVS detection application (see Section 4), a 300 kΩ maximum

or R

AVF

PULL-UP

300 kΩ maximum R

resistor value is recommended. With a 47 pF CL load capacitor and a

resistor, the AVF rise time is typically about 50 µs (see Figure 6).

AVF

Figure 6. AVF signal rising time measurement information

= 300 KΩ

STCC08

AVF driver

AVF

GND

AVF

Doc ID 14460 Rev 2 7/28

AVF

CL= 47 pF

R_AVF

90 % V

10 % V

STCC08 description AN2716

1.4.2 AC switch state detection principle

The AC switch state detection is achieved thanks to the STCC08 “power switch signal shaping” block. This block measures the current (I is the image of the AC switch voltage (V

) during both AC line cycle (V

Figure 7, three cases can be considered.

● Case 1: If the AC switch is off (V

= V

Line

line (see Section 1.5.1), flows through resistor R case, the STCC08 AVF output signal (V

● Case 2: If the AC switch is on (V

this case, the AVF output signal (V

● Case 3: If the AC switch is off and the AC line voltage falls to zero voltage, no I

current flows through the resistor R

AVF

≈ 0), no IAC current flows through the resistor RAC. In

) remains at low level state (GND).

AVF

. In this case, the AVF output signal (V

to zero level (GND).

Knowing the STCC08 IN input state, the MCU is then able to determine the AC switch state by analyzing the AVF signal (see Section 1.4.3).

Figure 7. AC switch failure detection principle

) through the STCC08 AC input, which

), a low I

current, in phase shift with the AC

for the both AC line polarities. In this

). As illustrated in

Line

) remains at high level state (+VCC).

AVF

) goes

AVF

The I

AC switch off

current follows the waveform of the voltage across the AC switch. The AVF signal

toggles between V

Figure 7). The I

Table 2. I

ACT

electrical parameter dispersion

ACT

The IAC peak current value (I

Load

ACT

-I

ACT

and zero level (GND) at a certain IAC current value noted as I

AC switch on

t (s)

Neutral

Line

Shunt

Load

LOAD

STCC08

ACS

Power switch signal shaping

electrical parameter dispersion is shown in Table 2.

AC-peak

Maximum (I

ACT_max

236 µA 82 µA

) must be lower than 2.2 mA (maximum IAC current

) Minimum (I

allowed through STCC08 AC input). Equation 2 defines the minimum resistor R (R example, with V

) to limit this IAC current in the worst case (if the AC load fails in short circuit). For

AC_Min

Line_rms_max

= 230 V + 10%, the RAC resistor value must be higher than

163 kΩ.

AVF

ACT

ACT_min

value

)

AVF

(see

8/28 Doc ID 14460 Rev 2

AN2716 STCC08 description

Equation 2

min

maxpeakAC

maxrmsLine

()

mAI

2.2

The resistor R

is used to detect the AC switch state whatever the AC load state is

Shunt

(connected or disconnected). Without this resistor, the STCC08 AVF signal remains at low level (GND) whatever the AC switch state when the AC load is disconnected (I detect the AC switch state when the AC load is disconnected (with the resistor R I

AC-peak

current remains higher than the I

ACT_Max

current (IAC current threshold to ensure the AC switch state detection - see Ta ble 2). Equation 3 defines the condition on R R

resistors to ensure a right AC switch states detection in the worst case (if the AC load

Shunt

is disconnected). For example, with V plus the R

resistor value must be lower than 1.24 MΩ.

Shunt

Line_RMS_Min

= 230 V - 10%, the RAC resistor value

= 0). To

Shunt

), the

and

Equation 3

2 X

maxACmaxShunt

maxACT

To limit the power dissipation by resistors R

minrmsLine

(236 µA)

and R

lower than ¼ W and their

Shunt

influences on the AC load, a 300 kΩ and 100 kΩ minimum value is recommended respectively under 230 V rms and 100 V rms AC line. Equation 4 and Equation 5 give the power dissipation for R

and R

in the worst case.

Shunt

Equation 4

)

maxRAC

)

maxrmsLine

minAC

Equation 5

)

maxRShunt

)

maxrmsLine

minShunt

1.4.3 AC switch failures detection during normal operation

Knowing the STCC08 IN input state, the MCU is able to determine the AC switch state by analyzing the AVF signal. Figure 8 andTable 3 give the AC switch failure modes according to the AVF signal state and the STCC08 IN signal state. In case of AC switch failure, the MCU can put the appliance in a safe configuration by switching off an appliance front-end relay.

Doc ID 14460 Rev 2 9/28

+ 19 hidden pages

ST AN2716 APPLICATION NOTE

Specifications and Main Features

Frequently Asked Questions

User Manual

Contents

1 STCC08 description

1.1 Main features

Figure 1. STCC08 block diagram

Table 1. STCC08 pin descriptions

1.2 STCC08 non-insulated and insulated application diagram

Figure 2. Un-insulated application diagram

Figure 3. Insulated application diagram

1.3 AC switch control

1.4 AC switch failure mode detection

1.4.1 STCC08 AVF output configuration

Figure 5. STCC08 AVF output configuration

Figure 6. AVF signal rising time measurement information

1.4.2 AC switch state detection principle

Figure 7. AC switch failure detection principle

1.4.3 AC switch failures detection during normal operation