STCC02-ED5 Datasheet, PDF (10/13 Pages) STMicroelectronics – CONTROL CIRCUIT FOR HOME APPLIANCE MCU BASED APPLICATION

STCC02-ED5
■ IMMUNITY IMPROVEMENT OF STCC02 AND ITS MICROCONTROLLER
DOOR
SWITCH
VCC
5
RELAY
COIL
VIN
3
2
VIN
VDD
5v REG
4
DS
Reset
RST \
Relay
Drive
STCC02
COM
1
VDD
3
RST \
4
MCU
VSS
1
Some basic rules can be applied to improve the STCC02 immunity in its application:
- The power grounds of V_CC and DS should be split from the signal ground V_SS.
(1)
- The STCC02 is placed as close as possible of the MCU;
(2)
- The supply capacitors would increase the system immunity by being placed closed to the blocks they
feed;
(3)
- Wide supply copper plane should be avoided to reduce sensitivity to radiated interferences.
More specifically with the STCC02 circuit,
- A decoupling capacitor can be put on the STCC02 pins SYN and the MCU reset pin;
(4)
- Depending of the PCB layout quality, others capacitors may be put on sensitive pins such as the output
regulator pin V_DD, the synchronization circuit pin ZVS or the door switch pin DS.
The power door switch is a well-identified electrical noise source for the electronic board. Its effect should
be reduced as much as possible. For instance, its power wires should be twisted together and split from
other wires. Its signal wires should be also twisted; and on the PCB, the V_CC forward track and the DS
signal reward track should be linked to reduce EMI on the signal DS.
(5)
■ ELECTROMAGNETIC COMPATIBILITY TEST CIRCUIT
Standards such IEC61000-4-X evaluate the electro-
magnetic compatibility of appliance systems. To test
the immunity level of the STCC02 to the IEC61000-4-
4 (transient bursts), a board representative of usual
control unit for microwave oven has been developed,
as shown on top of page 11. One characteristics of
MAINS
the IEC61000-4-4 test, is that no measurement
equipment can be connected to the tested system, as
0.5 kV to 4 kV
tr : 5 ns
tp : 50 ns
BURST COUPLE
it would corrupt the test results. That is why this board
includes a remote monitoring circuit based on optic
fibers. Thus, without any electrical link with an oscillo-
scope, it is possible to monitor the VDD voltage as
well as the RESET or the ZVS outputs of the
STCC02, during the IEC61000-4-4 test. This optical
link detects parasitic commutations of outputs as
short as 60ns.
With this board, and the burst generator coupled to the mains as specified in the IEC61000-4-4 standard
(see the above principle diagram), the STCC02 has been tested successfully at 4kV.
10/13