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

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

GT

G (6)

V (5)

CC

AC (4)

Power switch

signal shaping

Table 1. STCC08 pin descriptions

Gate driver

+

-

STCC08

AVF driver

IN (1)

R (7)

IG

AVF

AVF (2)

GND

GND (8)

IN

AVF

N/C

AC

1

2

3

4

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

5V

CC

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

8

R

IG

7

G

6

V

CC

5

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).

4/28 Doc ID 14460 Rev 2

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

CC

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

cc

Neutral

ACS

RAC

Load

RShunt

Line

Front end relay

G

V

CC

AC

Power switch

signal shaping

STCC08

Figure 3. Insulated application diagram

Neutral

ACS

G

Gate driver

+

-

+

-

AVF driver

V

CC1

IN

R

IG

VCC= 3.3V to 5V

IN

R

IG

AVF

GND

Un- insulatated

5 V or 3.3 V

Power supply

R

2

IG

R

V

CC

MCU

Power supply

Insulated

V

CC

V

CC2

Line

Load

RShunt

Front end relay

RAC

V

AC

CC

Power switch

signal shaping

STCC08

AVF driver

R

AVF

GND

OPTO1

I

G

R

1

V

CC1

R

AVF

OPTO2

V

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

IG

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

CC

) 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

G

j

), the IG gate

amb

Figure 4. Resistor R

AC switch I

R

130

120

110

100

90

80

70

60

50

40

30

20

10

0

-20-15-10-5 0 5 1015202530

value according to the minimum ambient temperature and

IG

GT

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

IG

appliance temperature range.

()Ω

IGTAC Switch:

IGT 10mA @ 25°C IGT 5mA @ 25 °C

T

amb_min

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

GT

(°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

R

V

CC

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

V

CC

R

AVF

I

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.

V

CC

STCC08

AVF driver

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

AVF

GND

I

AVF

AVF _max

V

CC

MCU

). Equation 1

CC_max

Equation 1

V

maxCC

or R

_

(

maxAVF

_

PULL-UP

)

mA5

resistor values modify the AVF signal rise time

or

AVF

RorR

_

PULLminAVF

-

>

minUP

_

I

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

R

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

R

= 300 KΩ

STCC08

AVF driver

AVF

GND

V

CC

R

AVF

C

L

V

AVF

Doc ID 14460 Rev 2 7/28

AVF

CL= 47 pF

t

R_AVF

90 % V

10 % V

CC

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

T

Figure 7, three cases can be considered.

● Case 1: If the AC switch is off (V

= V

T

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

T

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

AC

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

AC

), a low I

AC

current, in phase shift with the AC

AC

for the both AC line polarities. In this

). As illustrated in

Line

) remains at high level state (+VCC).

AVF

AC

) goes

V

T

I

AC

1

3

1

3

1

AVF

The I

V

AC switch off

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

AC

toggles between V

Figure 7). The I

Table 2. I

ACT

electrical parameter dispersion

ACT

I

ACT

The IAC peak current value (I

I

Load

I

ACT

-I

ACT

3

1

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

CC

2

AC switch on

t (s)

Neutral

Line

V

Line

Shunt

R

V

T

Load

I

LOAD

STCC08

G

ACS

AC

V

CC

R

I

AC

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

AC

V

CC

R

)

AVF

V

AVF

(see

8/28 Doc ID 14460 Rev 2

AN2716 STCC08 description

_

Equation 2

V

2

R

AC

>

min

_

X

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

AC

Shunt

AC

), the

and

Equation 3

2 X

RR

_

<+

_

maxACmaxShunt

I

maxACT

To limit the power dissipation by resistors R

V

__

minrmsLine

(236 µA)

AC

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

AC

in the worst case.

Shunt

Equation 4

2

(P

)

(V

=

maxRAC

R

)

maxrmsLine

__

minAC

_

Equation 5

2

(P

)

(V

=

maxRShunt

R

)

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

STCC08 description AN2716

Figure 8. AC switch failure detection

V

Line

V

Line

V

Line

VCC/COM

AC switch

Line

Load

RShunt

I

Load

RAC

STCC08

AC

AVF

VCC

R

AVF

V

AVF

VCC

V

AVF

I

Load

(a) AC switch state: off (no failure) if IN = 0 or open circuit failure if IN = 1

VCC

R

VCC/COM

I

AC switch

Line

Load

RShunt

Load

V

Line

RAC

STCC08

AVF

AC

AVF

V

AVF

VCC

I

Load

V

AVF

(b) AC switch state: on (no failure) if IN = 1 or short circuit failure if IN = 0

V

Line

VCC/COM

AC switch

Line

Load

I

Load

RAC

STCC08

AC

AVF

VCC

R

AVF

V

AVF

VCC

I

Load

V

AVF

V

Line

RShunt

(c) AC switch state: positive diode mode failure if IN = 0

VCC/COM

AC switch

Line

Load

RShunt

I

Load

RAC

STCC08

AC

AVF

VCC

V

AVF

R

AVF

VCC

I

Load

V

AVF

(d) AC switch state: negative diode mode failure if IN = 0

V

Line

10/28 Doc ID 14460 Rev 2

AN2716 STCC08 description

Table 3. STCC08 status truth table

MCU control (IN) AVF output state

(1)

AC switch state

0+V

0 Toggle from +V

(Except at each zero crossing of the AC line) Off (no failure)

CC

to 0 Diode mode

CC

0 0 Short-circuit

1 0 On (no failure)

1+V

1. The AVF output must be loaded with an external resistor (R

up input configuration (see Section 1.4.1).

(Except at each zero crossing of the AC line) Open-circuit

CC

AVF

1.5 AVF signal reading synchronization

1.5.1 Detection window width definition

When the AC switch is off (not controlled or failed in open circuit), an IAC current flows through the STCC08 AC input. The value of this current depends on R resistors, the AC line voltage, and the AC load impedance. The AVF signal toggles between V

and zero level (GND) for an IAC current value noted I

CC

impact on the AC switch state detection. If the STCC08 is not controlled (IN = 0) and the AVF signal is read when the I as failed in short circuit (see Table 3).

Figure 9. STCC08 AVF version when the AC switch is off

current is lower than I

AC

) or connected directly to the MCU, in pull

and R

AC

(see Figure 9). This has an

ACT

, the AC switch can be interpreted

ACT

shunt

Note:

V

Line

I

ACT

-I

ACT

AVF

ϕ

AC

A

00=

t

φ

is the phase shift between the AC line and the IAC current when the AC switch is off.

AC

t

1

AC

B

t

2

C

1

t

2

F

x=2

f

´=2

This phase shift is very low and can be neglected for most AC loads found in home appliances (see Appendix A).

t (s)

Doc ID 14460 Rev 2 11/28

STCC08 description AN2716

The t1 and t2 values are defined in Appendix A. For example, with RAC = R F = 50 Hz, V

AC_Line

respectively equal to 0.1 A and 90°, t

= 230 V, a minimum rms current and a phase shift of the AC load

and t2 are respectively 1.7 ms and 8.3ms.

1

Shunt

= 300 kΩ,

When the AC switch is failed in diode mode, the AC switch is on during only half of the AC line cycle for resistive load (the load current is in phase with the AC line voltage). In this case, the AVF signal falls to GND at each cycle of the AC line when the AC switch is on. However, with an inductive load, the load current (I

) falls to zero after the zero crossing

Load

of the AC line voltage (See Figure 10). This has an impact on the AC switch state detection. If the AC switch has failed in diode mode and the STCC08 AVF signal is read just after each zero crossing of the AC line voltage, the AC switch failed in diode mode will not be discriminated from the AC switch short circuit failure.

Figure 10. Load current and STCC08 AVF variation when the AC switch is failed in

diode mode

V

Line

I

Load

IN

t (s)

AVF

t (s)

t

Δ

Detection

t

READAVF

_

The STCC08 AVF signal should be read after the AC line peak voltage (t

Equation 6) and before the time t

to detect all AC switch states for most home

2

t

2

AVF_READ

) (See

appliance loads.

Equation 6

t

AVF_READ

Note: Note, if the STCC08 AVF signal is read between times t1 and t2 (see Figure 9), all the AC

switch failures will be detected but the AC switch failed in diode mode will be confused with the AC switch failed in short-circuit.

To detect the AC switch state when the STCC08 is controlled by a pulsed gate current, the MCU should store the IN signal state in a RAM register. This RAM register could be initialized at each zero crossing of the AC line voltage.

1

>

F

·4

Min

12/28 Doc ID 14460 Rev 2

AN2716 STCC08 description

1.5.2 AC switch state detection after IN signal removal

When the IN signal is removed (to turn on or off the AC switch), a parasitic detection of the AC switch state exists up to the next AC load current zero (see Figure 11 for AC inductive load case). As the AVF signal remains at a low-level state when the control is removed (I

≠ 0), the AC switch can be interpreted as an AC switch short circuit failure.

LOAD

Figure 11. Parasitic detection for inductive load

V

Line

I

Load

t (s)

IN

t (s)

I

AC

AVF

t

Delay

Parasitic detection

I

ACT

-I

ACT

t (s)

To ensure a correct detection of the AC switch state and to take into account the AC switch failed in diode mode, when the IN control is removed and whatever the AC load used, the AVF reading must be carried out according to Equation 7. For example, with F = 50 Hz, the AVF signal can be read after 20 ms when the IN control has been removed.

Equation 7

t

min

_

Delay

Note: Overall, the AVF signal should be read during several AC line cycles to avoid an incorrect

interpretation of the AC switch state.

1

>

F

Doc ID 14460 Rev 2 13/28

STCC08 consumption AN2716

2 STCC08 consumption

Equation 8, Figure 12, and Tabl e 4 define the maximum STCC08 current consumption

(I

DC_max

from the AC line and not from the STCC08 DC power supply. The current I current to turn on the AC switch, defined according to the external resistor R

Figure 13). The current I

I

Quiescent

100 µA. The AVF current, used to polarize the STCC08 AVF output is defined by the resistor R

AVF

Equation 8

Figure 12. STCC08 current consumption

). The current IAC is used only to detect the AC switch states. This current comes

is the gate

G

Quiescent

defines the STCC08 quiescent current. The maximum

current is specified at 2 mA. The maximum IN input current (I

IG

) is specified at

IN_Max

or by the MCU pull up resistor (see Equation 9).

IIIII

+++=

maxINmaxQuiesientmaxAVFG_maxmaxDC

____

Neutral

STCC08

AVF

I

Quiescent

R

AVF

I

AVF

I

G

VCC

value (see

I

DC

V

DC

MCU

I

R

AC

Line

Table 4. STCC08 consumption values

Load

R

Shunt

AC

GND

IN

I

IN

Parameter Definition Maximum value

I

G_max

I

Quiescent

I

AVF

I

IN

AC switch gate current

STCC08 current consumption 2 mA

AVF pin collector current

IN input current (to control the AC switch) 100 µA

Depends on the R

Figure 13

Depends on the R (I

AVF _max

= 5 mA). See Equation 9

Equation 9

V

maxCC

=

maxAVFI_

_

R

minAVF

_

=

V

_

R

Pull-up_min

maxCC

resistor. See

IG

resistor

AVF

14/28 Doc ID 14460 Rev 2

AN2716 STCC08 consumption

Figure 13. Maximum IG current (I

I

G_max

28 26 24 22 20 18 16 14 12 10

8 6 4 2 0

For example, with R

(mA)

30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120

= 30 Ω, V

IG

CC_max

current consumption is about 30 mA.

) versus resistor RIG value

G_max

R

(Ω)

IG_min

= 5.5 V and R

= 10 kΩ, the maximum STCC08

AVF

Doc ID 14460 Rev 2 15/28

Recommended component values AN2716

3 Recommended component values

Figure 14 and Table 5 show the application diagram and the recommended values to

implement the STCC08 device in the appliance according the AC line voltage.

Figure 14. Application diagram

Neutral

ACS

R

Load

RShunt

Line

Front end relay

Table 5. Recommended value

R

Shunt

R

AC

R

AVF

AC

G

V

CC

C

AC

IGT = 10 mA @ -20 °C 30 Ω ± 1% @ ¼ W 30 Ω ± 1% @ ¼ W

R

IG

I

= 5 mA @ -20 °C 68 Ω ± 1% @ ¼ W 68 Ω ± 1% @ ¼ W

GT

C 33 nF 33 nF

t

AVF_READ

t

(see Appendix A) 8.3 ms 8.9 ms

2_min

Δt

Detection_min

VCC= 3.3V to 5V

IN

R

IG

R

AVF

GND

IG

V

CC

R

AVF

MCU

STCC08

V

Line

230 V rms at 50 Hz 110 V rms at 50 Hz

300 kΩ @ ¼ W 100 kΩ @ ¼ W

10 kΩ @ ¼ W 10 kΩ @ ¼ W

5.1 ms 5.1 ms

3.2 ms 3.8 ms

V

GND

CC

16/28 Doc ID 14460 Rev 2

AN2716 ZVS detection application

4 ZVS detection application

The STCC08 “Power switch signal shaping” block can be used to detect the zero crossing of the AC line voltage. The resistor R as shown in Figure 15. The AVF signal toggles between V crossing of the AC line voltage.

Figure 15. ZVS detection

Neutral

ACS

V

AC

V

CC

AC

Line

Load

RShunt

R

AC

must be connected between AC input and the AC line

AC

G

Power switch

signal shaping

Gate driver

+

-

STCC08

and zero level at each zero

CC

3.3 V to 5 V

IN

R

IG

V

AVF driver

AVF

GND

CC

MCU

V

CC

V

AC

AVF

Δ

t

AVF

Equation 10 defines the maximal AVF signal low level width (Δt

the AC line voltage according to the value of resistor R

AC

.

Equation 10

⎛ ⎜

t

Δ

maxAVF

_

··1π

Ar

sin

X=

F

min

⎜ ⎝

RI

·

V

·2

rms

⎞

maxACmaxACT

__

⎟ ⎟

min

_

⎠

t (s)

) at each zero crossing of

AVF

Doc ID 14460 Rev 2 17/28

Electromagnetic compatibility (EMC) tests AN2716

5 Electromagnetic compatibility (EMC) tests

5.1 Demonstration board description

The STCC08 has been tested using a stand-alone demonstration board (see Appendix B) and according to IEC 61000-4-4. Appendix C and Appendix D give respectively the electrical schematic and the layout of the demonstration board. This demonstration board can work on 110 V / 230 V rms 50 / 60 Hz mains voltage. The STCC08 board includes:

● The STCC08

● The ACS108-6S

● An STLITE39 MCU.

● A capacitive power supply (C15 = 10 nF)

● An In-dart connector to load the MCU firmware

● Mechanical switches used to simulate different AC switch failures (diode mode, short

circuit and open circuit)

● A mechanical switch to control the STCC08 IN signal through MCU

● LEDs used to visualize the detected ACS failure modes.

● An AC load: light bulb (15 W at 230 V rms)

The STLITE39 MCU is used to turn the ACS108-6S on / off through the STCC08 and to analyze the AVF signal to power LEDs indicating AC switch states and failures (AC switch ON, diode mode, short circuit and open circuit).

Regarding the power supply, the maximum average current absorbed by the board is about 48 mA. A 2.2 µF C16 capacitor has been used to ensure the board works correctly (see

Appendix C).

5.2 IEC 61000-4-4 burst immunity test

5.2.1 Test conditions

● Ambient temperature: 25°C

● Relative humidity: 35%

5.2.2 Demonstration board immunity test

The AC line input X2 capacitor C15 (10 nF) is used to help avoid triggering the AC switch (ACS108-6S). The MCU program reads the AVF signal at each AC line peak voltage (see

Figure 16). The demonstration board is validated if the AVF signal remains at the same level

during three consecutive AC line cycles.

18/28 Doc ID 14460 Rev 2

AN2716 Electromagnetic compatibility (EMC) tests

Figure 16. AVF signal detection

Timer

> T/4 ms

T/2 ms

ZVS delay

Read AVF and timer off

ZVS detection => Timer on

ZVS delay

ZVS detection => Timer on

The demonstration board and mains wires are placed 10 cm above the ground reference. The mains wire is shorter than 1 m. Each operating cycle has been tested (load off and on). The demonstration board supports burst levels higher than 4 kV without spurious triggering of the ACS or ST7Lite3 MCU loss whatever the coupling mode (to L, N, etc.).

5.2.3 Advice to improve the application immunity

V

AC

Read AVF and timer of

To improve the application performance in term of EMC, the software must be EMC oriented (for more information please refer to the application note AN1015):

● Auto-recovery routine. At each reset interrupt, the program must check if the data

stored in the RAM are as scheduled or not. A reset can occur without the supply voltage having fallen below V

(data retention parameter). In this case, a full start-up

RM

is not necessary, and the program can keep working with the previous RAM data. This is helpful to avoid missing load control and the AC switch status when a reset occurs due to an EMI problem, for example. If the checked RAM registers are not as expected, then a complete initialization procedure is launched. If the RAM area is adequate, then a “smart reset” can be performed. Only the registers that are used to store internal subroutine variables are cleared. Only the main registers keep their previous values (AC switch status, AC switch control …).

● Using the watchdog properly. Enable the watchdog as soon as possible after reset

and never refresh the watchdog in an interrupt routine.

● Secure the unused program memory area. Fill the unused memory locations with

code that forces a watchdog reset or jumps to a known program

location if you do not

want to generate a reset.

● Input filtering. It is recommended that the AVF signal be read during several AC line

cycles.

Doc ID 14460 Rev 2 19/28

Conclusion AN2716

6 Conclusion

This application note illustrates how designers can maximize the STCC08 performance in their appliances especially for AC switch state detection and EMI robustness.

This document describes the STCC08 device and gives technical recommendations about the STCC08 implementation in the appliance.

References

1. T. Castagnet, B. Cheron, A. Edet, “AC power management in homes appliances: a

reality to save energy and increase safety”, IATC 2006, Rosemont, Illinois, USA.

2. L.Gonthier, "A New Solid State Switch for Home Appliances", International Appliance

Technical Conference, IATC 1999, West Lafayette, Indiana, USA.

3. G. Benabdelaziz, P. Paillet, “AC STCC08 - Safety supervisor for home-appliance AC

switches”, PCIM 2009, Nuremberg, Germany.

20/28 Doc ID 14460 Rev 2

AN2716 Timing definitions

Appendix A Timing definitions

When the AC switch is OFF (not controlled or failed in open circuit), an IAC current flows through the STCC08 AC input. The value of this current depends on RAC and Rshunt resistors, the AC line voltage and the AC load impedance. The AVF signal toggles between VCC and zero level (GND) for an IAC current value noted IACT (see Figure 17).

Figure 17. Detection window width of the AC switch state

V

Line

I

AC

t (s)

-I

I

ACT

AVF

ϕ

AC

A

00=

t

Considering Figure 18, the I

t

1

current variation, when the AC switch is off, is defined

AC

according to Equation 11 where I

B

AC_peak

R and L are AC load characteristics, and φ AC line voltage.

t (s)

C

1

t

2

t

2

F

x=2

f

´=2

is the peak IAC current, F is the AC line frequency,

is the phase shift between IAC current and the

AC

Doc ID 14460 Rev 2 21/28

Timing definitions AN2716

Figure 18. AC load model definition

Neutral

Line

V

AC switch

V

CC

STCC08

Load

LR

R

AC

I

AC

Power switch

signal shaping

R

Shunt

Equation 11

() ( )

_

Considering Equation 11, t1 and t2 times are given respectively by Equation 12 and

Equation 13 in the worst case (to avoid the false detection of an AC switch failed in short-

circuit any time).

tFItI ϕπ -=···2sin·

ACpeakACAC

Equation 12

⎛

=

t ϕ

_1

Max

1

xx

2

π

⎡

Ar

⎢

F

⎢

min

⎣

I

⎜

sin·

⎜

I

⎝

⎞

_

maxAC T

⎟

+

⎟

__

minPeakAC

⎠

AC

⎤ ⎥

max_

⎥

⎦

Equation 13

⎛

F

max

⎡

⎜

⎢

-

⎜

⎢

⎝

⎣

t

=

_2

min

1

xx

2

π

Ar

⎛

I

⎜

sin·

⎜

I

⎝

⎞

_

maxACT

⎟

+

ϕπ

⎟

__

minPeakAC

⎠

⎞

⎤

⎟

⎥

_

maxAC

⎟

⎥

⎠

⎦

I

AC_peak_min

defines the minimum peak IAC current through the STCC08 AC input to ensure the AC switch state detection. This current must be higher than the maximum specified I parameter (I

ACT_max

) in order to detect the AC switch state in the worst case (when the AC load is disconnected). Equation 14 defines this condition. Indeed, when the AC load is disconnected, the I = R 10%, the I

= 300 kΩ (see Equation 2 and Equation 3), F = 50 Hz and V

Shunt

AC_Peak_min

current is limited by RAC and R

AC

is 465 µA.

Equation 14

·2

I

=>

minPeakAC

__

V

φAC is the phase shift between the AC line and the IAC current when the AC switch is off. As

the resistor R

value is higher than the most AC load impedances found in home

Shunt

appliances, this phase shift depends only on the AC load characteristic and resistor R

Figure 19 gives Fresnel's diagram for R

22/28 Doc ID 14460 Rev 2

minrmsLine

__

+

RR

maxACmaxShunt

__

I

ACT_max (236 µA)

= 0 and RAC ≠ 0 for the circuit in Figure 18 to

AC

resistors. For example, with RAC

Shunt

Line_RMS_min

ACT

= 230 V -

.

AC

AN2716 Timing definitions

define the φAC phase shift. If RAC = 0 Ω, the rms IAC current and φAC phase shift are equal respectively to rms I R

≠ 0 Ω, the rms IAC current (I

AC

resistor R the maximum φ

and the AC load impedance. In this case, and according to Fresnel's diagram,

AC

Load

current (I

Load_RMS

AC_RMS

) and φ

phase shift of the AC load. If

Load

) and φAC phase shift depend on the value of the

phase shift is defined by Equation 15 and Equation 16.

Equation 15

x

π

2

V

rmsLine

_

x

=

xx

rmsAC

() ()

ϕ

sin

AC

=

π

2

sin

IFLIFL

xxxx

ϕ

Load

rmsLoad

__

Equation 16

⎞ ⎟ ⎟ ⎠

AC_max

Arc ϕϕ sinsin

⎛

I

rms_maxAC

_

⎜ ⎜

I

rms_minLoad

_

⎝

()

x=

Load_max

For example, in the worst case, if the minimum rms current (I

φ

phase shift of the AC load are respectively 0.1 A and 90°, the maximum φAC phase

Load

shift is about 1.26 °. This phase shift is very low and can be neglected as most AC loads have rms current higher than 0.1 A and phase shift lower than 90°. With R = 300 kΩ and F = 50 Hz, t

1_max

and t

are respectively 1.7 ms and 8.3 ms.

2_min

Figure 19. Fresnel’s diagram

V

Line_RMS

φ

AC

φ

Load

R . I

Load_RMS

(RAC= 0)

(R + RAC).I

AC_RMS

2 . p .f . L .I

Note: If the AC load is a resistor, or is disconnected, the I

(φ

= 0).

AC

The STCC08 AVF signal should be read after the AC line peak voltage and before the t time to detect all AC switch states for most home appliance loads.

Load_min

2 . π .f .L .I

Load_RMS

current is in phase with the AC line

AC

) and the maximum

= R

AC

Shunt

AC_RMS

2

Doc ID 14460 Rev 2 23/28

Demonstration board component layout AN2716

Appendix B Demonstration board component layout

Figure 20. Demonstration board component layout

24/28 Doc ID 14460 Rev 2

AN2716 Demonstration board schematic

Appendix C Demonstration board schematic

Figure 21. Demonstration board schematic

COM/VCC

ON/OFF

COM/VCC

D9

ON

D8

CC

OPEN

D7

D6

DIODE

D5

STCC08 CNTRL

C10

10n

ZVS

C11

10n

C12

10n

C13

10n

ST CC0 8 CNTRL

SW5

COM/VCC

ST CC0 8 CNTRL

AC

OUT

TP6

Gate

ACS

U3

D4

1N4007

SW3

D3

SW2

1N4007

SW4

2

1

J2

J2 -Light Bulb- 15W

TP7

AC

56k

R4

56k

R3

56k

R2

56k

R1

56k

R5

R6

R5

R6

56k

R7

R8

R7

R8

J3

COM/VCC

RST

TP9

IN

IN_MCU

Com/VCC

Com/VCC TP3

TP3

COM/VCC

2

F1

FUSE/1A

TP1

N

GND

ZVS

TP5

TP4

TP5

TP4

ZVS

100n/16V

C2

+

C1

2200uF/25V

D1

5V6 - 0.5W

1

Varistor 375V

R13

C15

J1

R12

1N4148

D2

R11

C16

2.2uF - X2

R10

R14

39 - 3W

R9

10n - X2

123

AC Mains

COM/VCC

C16

1n

68k

TP8

AVF

AC

68k

C14

100n

4

68k

AC

U1

5

68k

100n/16V

C3

COM/VCC

TP2

L

C9

C8

R24

3

120n/16V

NC

GATE6VCC

43

Gate

INDART CONNECTOR :HE10

R22

470

R21

470

R20

470

R19

470

LS

R18

470

19

20

OSC2

OSCI/CLKIN

U2

VDD

VSS

2

1

COM/VCC

1.2K

2

1

IN

AVF

GND

RIG

8

7

R23

PA0(HS)18PA1(HS)17PA2(HS)16PA3(HS)15PA5(HS)

RST

3

RST

IN_MCU

STCC08

4

R17

PB0/AIN0

5

PB1/AIN1

PB2/AIN2

PB1/AIN1

PB2/AIN2

6

IN_MCU

R16

11

13

12

13

12

14

PA4(HS)

PA6(HS)

PA4(HS)

PA6(HS)

PA7/TDO

ST7LITE39

PB6/RDI10PB5/AIN59PB4/AIN48PB3/AIN3

7

TP12

C7

100n/16V

0

C6

10n/16V

C5

10n/16V

0k

C4

10n/16V

R15

680k

SW1

123456789

10

123456789

10

J3

Doc ID 14460 Rev 2 25/28

Demonstration board circuit layout view AN2716

Appendix D Demonstration board circuit layout view

Figure 22. Top layer view

Figure 23. Bottom layer view

26/28 Doc ID 14460 Rev 2

AN2716 Revision history

Revision history

Table 6. Document revision history

Date Revision Changes

26-Nov-2008 1 Initial release.

16-Jun-2010 2 Revised Section 1.5.1 and Appendix A. Added References.

Doc ID 14460 Rev 2 27/28

AN2716

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28/28 Doc ID 14460 Rev 2

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

Figure 8. AC switch failure detection

Table 3. STCC08 status truth table

1.5 AVF signal reading synchronization

1.5.1 Detection window width definition

Figure 9. STCC08 AVF version when the AC switch is off

1.5.2 AC switch state detection after IN signal removal

Figure 11. Parasitic detection for inductive load

2 STCC08 consumption

Figure 12. STCC08 current consumption

Table 4. STCC08 consumption values

3 Recommended component values

Figure 14. Application diagram

Table 5. Recommended value

4 ZVS detection application

Figure 15. ZVS detection

5 Electromagnetic compatibility (EMC) tests

5.1 Demonstration board description

5.2 IEC 61000-4-4 burst immunity test

5.2.1 Test conditions

5.2.2 Demonstration board immunity test

Figure 16. AVF signal detection

5.2.3 Advice to improve the application immunity

6 Conclusion

References

Appendix A Timing definitions

Figure 17. Detection window width of the AC switch state

Figure 18. AC load model definition

Figure 19. Fresnel’s diagram

Appendix B Demonstration board component layout

Figure 20. Demonstration board component layout

Appendix C Demonstration board schematic

Figure 21. Demonstration board schematic

Appendix D Demonstration board circuit layout view

Figure 22. Top layer view

Figure 23. Bottom layer view

Revision history

Table 6. Document revision history