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STCC02-ED5
CONTROL CIRCUIT FOR HOME APPLIANCE MCU BASED APPLICATION
APPLICATIONS

Microwaves oven analog and power driver control Home Appliance digital control
FEATURES Wide range input supply voltage operation: 7 to 27 V 5 V 10% full tolerance Voltage Regulator MCU reset circuit with activation delay timer and 45s digital noise filter Highly immune and 30 s filtered Zero Voltage Synchronization Door Closed detection adaptation One 100 mA fan relay coil driver with demagnetizing diode One 100 mA magnetron relay coil driver with demagnetizing diode including down lock circuit based on fan drive output state One 17 mA buzzer driver Ambient temperature: - 10 to 80 C BENEFITS Higher module compactness with reduced component count Drastic reduction of soldered pins on the board for faster module assembly time and lower use of lead High ESD robustness and transient burst immunity compliant with IEC61000-4 standards Enhanced functional reliability Accurate MCU supply for better Analog to Digital Conversion Enhanced circuit parametric quality Easy to design for short time to market
DIP-16
Table 1. Order Code Part Number STCC02-ED5
Marking STCC02-E
Figure 1: Pin Configuration (ball side)
VIN DLC SYN DS MAG2 FAN1 VCC COM
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
VDD /RST ZVS CDD IN1 IN2 IN3 BUZ3
December 2004
REV. 1
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Figure 2: STCC02 Based Application Diagram
Line
VCC
MAINS
VIN CDD
Neutral
VIN VCC JP RZV
DOOR SWITCH
5V Regulator Reset with delay Zero volts sync. Door closed detection Magnetron driver Fan driver
VDD /RST ZVS CDD IN2 IN1 IN3
CDD VSS /RST NMI P04 P01 P02 P03
CUP
DLC SYN DS MAG2 FAN1 VCC COM
VCC
MAGNETRON RELAY
FAN RELAY
Buzzer driver
BUZ3
MCU
BUZZER
Figure 3: Circuit Block Diagram
VIN DLC SYN DS MAG2 FAN1 VCC COM
Buzzer driver 5V Regulator Reset with delay Zero volts sync. Door closed detection Magnetron driver Fan driver
VDD /RST ZVS CDD IN2 IN1 IN3 BUZ3
FUNCTIONAL DESCRIPTION The STCC02 is a control circuit embedding most of the analog & power circuitry of a microwaves oven control module. It interfaces the micro-controller with the power and process sections of the oven.
The voltage supply The 5V voltage regulator supplies the micro-controller MCU: especially functions such as the timer, the Analog-Digital Converter ADC, and the low current outputs. Since all the high-current outputs sink their current from a different voltage supply, this regulator does not need to be oversized. Its average output current can vary from 5 to 20 mA.
RSENSE VIN
Over current limiter
1.25V Reference
+
R1
R2
VDD
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Its output voltage accuracy, that contributes to the ADC accuracy of the MCU, is better than 10 % in the whole operating range of the temperature TAMB, the load current IDD and the input voltage VIN. The STCC02 input voltage range from 7 to 27 V; and its DC output current is less than 20 mA to keep the internal dissipation compatible with thermal package capability. The regulator includes also an over current limiter to prevent high current conditions during the power up inrush or the output short circuit. This limiter is made of a serial shunt resistance as current sensor and a circuit that regulates the input over current.
The reset circuit This circuit ensures a Low Voltage Detection (LVD) of the output voltage of the regulator. Most microcontrollers have an active RESET pin in the low state: so, the /RST pin will be active at low state.
VDD
VDD
VH = 4.25 V VL = 3.75 V
VH VL
PROGRAMMABLE DELAY NOISE FILTER
VDD /RST 500
circuit output RST\ TDW ~ 40 s internal latch output TUP = 6 ms CUP = 47 nF
DLC
External Capacitor CUP
If CUP = 47 nF, TUP = 6 ms
The reset circuit senses the regulator voltage VDD. Its comparator with hysteresis achieves this task. The /RST pin is high when VDD is higher than the high threshold VH = 4.25 V; and is low when the VDD decreases below the low threshold VL = 3.75 V. The comparator output changes are filtered for a high immunity. When the reset is disabling (VDD > VH), the /RST signal rises after the delay time TUP. This delay is set by an external capacitor CUP connected to the DLC pin: TUP = 6 ms for CUP = 47 nF. When the reset is enabling (VDD < VL), the /RST signal is falling after a delay time TDW that is internally set at 40 s when CUP = 47 nF.
The Zero Voltage Synchronization ZVS Circuit
VDD ZVS 20 s Filter S1 RZV VCC
AC LINE
SYN
25 k S2
500 Q
VZVS
VTF
100 k
COM
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The Zero Voltage Synchronization ZVS circuit generates a low frequency clock using the AC line cycles (20 ms on 50 Hz or 16.7 ms on 60 Hz). This clock allows the MCU to generate the cooking timings and to reduce the magnetron inrush current by powering it on at the AC line peak voltage.
RZV = 10 k; VCC = 15 V; ICC = 20 mA
VZVS
50s 115s
VTF 2V / div 40s / div FALLING EDGE RISING EDGE
The input pin SYN is an image of the mains voltage and is usually connected to the supply transformer through a resistor RZV. The circuit is protected against fast line transients because its state change will act on the whole MCU routines: a 30 s filter is implemented giving a higher immunity to the MCU circuit. Since the ZVS pin connected to the Non Maskable Interrupt NMI or INT\ of the MCU, its falling edge is the active counting event. The delay between the real Zero Crossing event and this ZVS falling edge depends on the internal filtering time, the resistance RZV, the transformer, the rectifier drop voltage VF, the VCC supply load and the temperature. The STCC02 contribution to this delay can be evaluated by measuring the delay between its input voltage VTF and its output voltage VZVS. When using VF = 0.8V, RZV = 10 k, VCC = 15V, ICC = 20 mA, it is about 50 s on rising voltage VTF and 115 s on falling voltage VTF.
Door closed detection circuit
VDD VCC EMI Filter DS Door Switch
25 k 50 k 500
VDD CDD
The magnetron of the oven can be powered only if the door is closed in order to protect the oven user. This safety feature is ensured mechanically by putting the door switch in series with the magnetron relay coil supply. For redundancy purpose, the Door Closed Detection CDD signal is also transmitted to the MCU. Since the DS input detects the door state from an electromechanical switch, a spike suppressor is added to increase its robustness. Its EMI immunity in off state (open door) is increased thanks to a 50k pull down resistor that maintains the DS signal in low state. When DS is high (24V), CDD signal is also in high state (5V).
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The magnetron relay coil driver
DS Demagnetizing Diode VDD IN2
15 k
MAG2 Relay Transistor
FAN1
This robust driver interfaces a DC relay coil and an MCU output. The relay coil power is rated up to 1.2 W for VCC = 12V. Its output stage is made of a transistor and a demagnetization diode. The transistor's reference is to the power ground COM and has a DC current rating of 100 mA. Its collector is connected to the outputs MAG2. The diode is connected between the output pin MAG2 and the Door Switch pin DS. To enhance safety rules and to prevent any unventilated operation of the magnetron, the relay coil magnetization is enabled by the fan conduction state that becomes a logic signal FAN1\. Furthermore, its demagnetization node is connected to the door switch pin DS: when the oven door is open, the coil of the magnetron relay is immediately disconnected from the relay supply VCC to switch off these heating loads. The boolean rule of the magnetron relay operation becomes: (Magnetron relay ON) = DS.IN2.FAN1\.
VCC 1.5 k VDD IN3 50 k BUZ3 Buzzer Transistor IN1 15 k Demagnetizing Diode VDD
VCC
FAN1 Relay Transistor
Fan relay coil driver This robust driver interfaces a DC relay coil and an MCU output. The relay coil power is rated up to 1.2W for VCC =12 V. Its output stage is made of a transistor and a demagnetization diode. The transistor is referred to the ground COM, has a DC current rating of 100 mA; and its collector is connected to the output FAN1. The diode is connected between the output pin FAN1 and the supply pin VCC.
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Buzzer driver The MCU can drive a warning buzzer with a 50% PWM signal. The buzzer driver amplifies this signal in current and translates it from the 5V MCU output to the VCC supply to produce the right sound level from the buzzer. The output stage is made of a transistor and a 1.5 k resistor. The transistor is referred to the power ground COM and is connected by its collector to the output BUZ3. It has a DC current rating of 17 mA and runs up to 5 kHz. Finally, the resistor is connected between the BUZ3 and VCC pins to discharge the capacitance of the buzzer at turn off and in off state.
Table 2: Absolute Ratings (limiting values) Symbol VDD VIN VSYN VMO VI VO Pin VDD VIN Parameter name & conditions Output supply voltage Input supply voltage Value - 0.3 to 6 - 0.3 to 30 - 0.3 to 30 - 1 to 30 - 0.3 to 30 - 0.3 to VDD + 0.3V - 0.3 to VDD + 0.3V 120 120 100 15 10 1 5 0.65 - 10 to 85 - 10 to 150 - 25 to 150 Unit V V V V V V V mA mA mA mA mA mA kHz W C C C
VDS, VCC DS, VCC
Door switch and power supply voltage AC input voltage, RZV = 10k SYN BUZ1, MAG2, FAN1 Output voltage IN1, IN2, IN3 ZVS, CDD, /RST DS, VCC Input logic voltage Output logic voltage Maximum sourced current pulse, tp = 10ms Maximum sunk driver current pulse, tp = 1ms Maximum DC sourced current Maximum driver diode reverse current Maximum DC sourced current Maximum demagnetization diode reverse current Maximum buzzer frequency Operating dissipation, DIL-16 package Operating ambient temperature, DIL-16 Operating junction temperature Storage junction temperature
(1)
MAG2, FAN1 IM BUZ3 MAG2, FAN1 FMAX PDIS TAMB TJ IN3, BUZ3 All AII All
Note 1: Refer to the Application Recommendations for the calcultation of the functional dissipation.
Table 3: Electromagnetic Compatibility Ratings (TJ = 25C, according to typical application diagram of page 1, unless otherwise specified) Symbol VESD Node All pins Parameter name & conditions ESD protection, MIL-STD 883 method 3015, HBM model Value 2 Unit kV
Table 4: Thermal Resistance Symbol Rth(j-a) Parameter DIL-16 thermal resistance junction to ambient Copper thickness = 35m Value 100 Unit C/W
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Table 5: Tentative Electrical Characteristics (TJ = 25C, VCC = 12V, unless otherwise specified) Symbol Conditions Min. Typ Max. Unit Voltage supply IDD = 5 to 20mA Tamb = - 10 to 80C VDD Output voltage supply 4.5 5 5.5 V VIN = 7 to 27V CDD = 10F VIN Input supply voltage 7 27 V VIN Quiescent supply current VDD = 5V, IDD = 0 (open) 1.25 2.5 mA Internal circuit current VIN1 = VIN2 = VIN3 = VDD VIN 1.9 3 mA (IIN - IDS) IDD = 20 mA VDD = 0V VIN Limiting input current 45 90 mA Output in short circuit Reset circuit Disabling reset threshold 4.25 4.5 V Enabling reset threshold 3.3 3.75 V Threshold hysteresis 0.3 0.5 V /RST Disabling reset delay CUP = 47nF 1 6 ms time Enabling reset daly time CUP = 47nF 45 s Zero Voltage synchronization circuit SYN Transition filtering time VTF = 0 to VCC rising and 10 30 70 s ZVS falling step SYN Transition threshold 0.4 0.6 0.9 V SYN Input activating current RZV = 10k,VSYN = 24V 0.8 2 mA Door closed detection circuit Closed door detection 7 27 V Open door detection 0.5 V DS Internal input current VDS = 27V 1.6 2.3 mA Door closed detection, zero voltage synchronization, reset circuits CDD /RST High level output voltage 0.8 VDD V ZVS Low level output voltage 0.2 VDD V Fan relay coil driver IN1 Input activating current VIN1 = VDD 300 800 A 1 1.5 V On state output voltage ION = 100mA, VIN1 > 3.5V FAN1 Off state output voltahe VIN1 < 1V, RL = 110 0.9 VCC VCC V Magnetron relay coil driver IN2 Input activating current VIN2 = VDD, VFAN1 < 1.5V 300 800 A ION = 100mA, VIN2 > 3.5V 1 1.5 V On state output voltage V MAG2 FAN1 < 1.5V Off state output voltage VIN2 < 1V, RL = 110 0.9 VDS VDS V Buzzer driver Input activating current VIN3 = VDD 60 200 A IN3 Buzzer PWM frequency Duty cycle = 50% 2 kHz Off state output voltage VIN1 < 1V 0.9 VCC VCC V BUZ3 On state output voltage ION = 10mA, VIN3 > 3.5V 1.2 1.8 V Buzzer resistance to VCC 1.5 k
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Pin
Name
VDD VIN ISQ ISM IIN_SC VH VL VHYS TUP TDW TD VTH ISYN VDS H VDS L IDS
VOH VOL IIN1 VON VFAN1 H IIN2 VON VMAG2 H IIN3 FBUZ VBUZ3 H VON RBUZ
STCC02-ED5
DC CHARACTERISTICS FIGURES Figure 4: Regulator characteristic with Tj = 25C and VIN = 12V
5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 0
Voltage regulation
VDD (V)
Current Limitation
IDD (mA)
10
20
30
40
50
Figure 5: Regulator output voltage versus its junction temperature with VIN = 12V
5.5 5.4 5.3 5.2 5.1 5 4.9 4.8 4.7 4.6 4.5 -20 0 20 40 60 80 100 120
VDD (V)
IDD=20mA
IDD=5mA
Tj (C)
Figure 6: Regulator output voltage versus its input voltage with IDD = 5 and 20 mA and TJ = 25C
5.5 5.4 5.3 5.2 5.1 5 4.9 4.8 4.7 4.6 4.5 5
VDD (V)
IDD=20mA IDD=5mA
VIN (V)
10
15
20
25
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APPLICATION RECOMMENDATIONS
EVALUATION OF THE STCC02 DISSIPATION IN ITS APPLICATION In order to define accurately at which maximum input supply voltage the STCC02 can work safely, the dissipated power has to be evaluated. Indeed, the STCC02 device can withstand voltages up to 30V, as specified in the table 1 "ABSOLUTE RATINGS" section. However, when the VIN voltage is high, it will also increase the power dissipation PDIS and the junction temperature TJ of the whole circuit. For the evaluation of the maximum junction temperature, the following equation should be used to calculate dissipated power:
PDIS = (VIN - VDD) x IDD + VIN . IQ + VON x (IM@FAN1 + IM@MAG2 + IM@BUZ3) + --------------------------- x
Indeed, the power dissipation is mainly due to the regulator and to the currents sunk by the three driver outputs FAN1, MAG2, and BUZ3. Furthermore, the input voltage VIN is linked to the relays conduction in most applications. When the relay coils are driven, the storage supply capacitor is discharged and VINis no longer equal to the peak voltage of the transformer secondary winding. In this case, VIN should approach the average value of the secondary voltage. This value is then approximately 36% lower that in stand-by operation, as explained by the following equation: 2 VIN (relays_on) -- x VIN (relays_off) When the relays are off, the dissipation losses formula is:
IN ON PDIS = (VIN - VDD) x IDD x IQ + --------------------------- x
V IN - V ON 1.2 x R BUZ
V -V 1.2 x R BUZ
For instance if VIN = 27V, VDD = 5V, IQ = 2.5mA, IDD = 20mA, RBUZ = 1.5k, = duty cycle = 50%, the dissipated power in the STCC02 is evaluated at 0.68W. When the relays are on, the full formula of the dissipation losses is applied. For instance in the same AC line conditions with the relays on, VIN drops down to 17.5V. Considering IM BUZ3 = 10mA, IM FAN1 = IM MAG2 = 100mA and VON = 1.5V, the dissipated power in the STCC02 becomes 0.67W. The maximum junction temperature is given by:
TJ max = TAMB max + Rth (j - |a) x PDIS
The maximum allowed input supply voltage is then chosen in order to keep the junction temperature below its maximum operating value 150C. Since the maximumjunction temperature is 150C, the maximum ambient temperature TAMB is 80C in this application, and the thermal resistance is 100C/W, the maximum allowed dissipation becomes 0.70 W. The two dissipation cases described above are compatible with the package dissipation capability. Otherwise, the ambient temperature TAMB, the input voltage VIN or the load current IDD should limited by design to meet the circuit thermal requirements.
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IMMUNITY IMPROVEMENT OF STCC02 AND ITS MICROCONTROLLER
2
DOOR SWITCH VCC VIN VIN 5v REG VDD VDD
3 5
DS Reset RST \
4
3
RST \
4
RELAY COIL Relay Drive
MCU STCC02
VSS COM 1 1
Some basic rules can be applied to improve the STCC02 immunity in its application: (1) - The power grounds of VCC and DS should be split from the signal ground VSS. - 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 VDD, 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 VCC 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 electromagnetic compatibility of appliance systems. To test the immunity level of the STCC02 to the IEC61000-44 (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 the IEC61000-4-4 test, is that no measurement equipment can be connected to the tested system, as 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 oscilloscope, 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.
MAINS 0.5 kV to 4 kV tr : 5 ns tp : 50 ns BURST COUPLE
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STCC02-ED5
MAINS1
TR1
12V 1.5VA
VCC
D1 Vin 1N4002
C1 220uF D2~D5 1N4002 C6 R1 10k
22nF VCC DOOR SWITCH
ZVS CIRCUIT COMPATIBILITY WITH THE POWER SUPPLY RECTIFIER BRIDGE In some cases, the operation of the ZVS circuit may require a small capacitor CZV on the pin SYN in addition to the resistor RZV. The diodes of the full wave rectifier bridge may have a low speed and may switch off with recovery charges that create spikes on the pin SYN as shown on the waveforms below. With a10k - 22nF RC circuit, the ZVS circuit becomes immune to such spikes.
VCC
VIN
4ms/div
VIN CUP DLC SYN RZV CZV
VZVS
5V Regulator Reset with delay Zero volts sync. Door closed detection Magnetron driver Fan driver
2V/div
VDD
ZVS
IN2 IN2
VTF
5V/div
COM
Buzzer driver
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Figure 7: DIP-16 Package Mechanical Data DIMENSIONS REF.
I L b Z e B e3 E D F b1 a1
Millimeters Min. Typ. Max. Min. 0.020 1.65 0.030 0.50 0.50 20 8.5 2.54 17.78 7.1 5.1 3.3 1.27 0.51 0.77
Inches Typ. Max. 0.065 0.020 0.001 0.787 0.335 0.1 0.7 0.280 0.201 0.130 0.050
a1 B b b1 D E e e3
16 1
9 8
F I L Z
Table 6: Ordering Information Part Number STCC02-ED5 Marking STCC02-E Package DIP-16 Weight 1g Base qty 25 Delivery mode Tube
Table 7: Revision History Date 05-Dec-2004 Revision 1 First issue Description of Changes
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Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners (c) 2004 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America www.st.com
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