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? 1/13 STCC02-BD5 control circuit for home appliance mcu based application october 2004 rev. 3 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 45 s 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 cir- cuit based on fan drive output state one 10 ma buzzer driver ambient temperature: - 10 to 85 c dip-16 table 1. order code part number marking STCC02-BD5 stcc02-b 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 figure 1: stcc02 based application diagram mcu c dd c dd v dd v in c up v in v cc v cc jp v cc r zv magnetron relay fan relay door switch mains neutral buzzer /rst dl c zvs syn c dd ds in 1 mag 2 in 2 fan 1 in 2 in 2 in 3 v cc buz 3 com /rst nmi p 03 p 02 p 01 p 04 v ss 5v regulator reset with delay zero volts sync. door closed detection magnetron driver fan driver buzzer driver
STCC02-BD5 2/13 functional description the stcc02 is a control circuit embedding most of the analog & power circuitry of a microwaves oven con- trol 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. 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 t amb , the load current i dd and the input voltage v in . the stcc02 input voltage range from 7 to 27 v; and its dc output current is less than 20 ma to keep the inter- nal 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 micro- controllers have an active reset pin in the low state: so, the /rst pin will be active at low state. figure 2: pin-out connections figure 3: block diagram v in dl c syn ds mag 2 /rst cdd in 3 buz 3 in 1 in 2 zvs v dd 1 2 3 4 5 6 7 89 12 11 10 13 14 15 16 com v cc fan 1 v dd v in /rst dl c zvs syn c dd ds in 1 mag 2 in 2 fan 1 in 2 in 2 in 3 v cc buz 3 com 5v regulator reset with delay zero volts sync. door closed detection magnetron driver fan driver buzzer driver dl c if c = 47 nf, t = 6 ms up up external capacitor c up /rst programmable delay noise filter v dd v dd v h v = 4.25 v h 500 ? v l v = 3.75 v l t dw ~ 40 s v dd circuit output internal latch output t up = 6 ms c up = 47 nf rst\ t dw ~ 40 s v dd circuit output internal latch output t up = 6 ms c up = 47 nf rst\
STCC02-BD5 3/13 the reset circuit senses the regulator voltage v dd . its comparator with hysteresis achieves this task. the /rst pin is high when v dd is higher than the high threshold v h = 4.25 v; and is low when the v dd decreases below the low threshold v l = 3.75 v. the comparator output changes are filtered for a high immunity. when the reset is disabling (v dd > v h ), the /rst signal rises after the delay time t up . this delay is set by an external capacitor c up connected to the dl c pin: t up = 6 ms for c up = 47 nf. when the reset is enabling (v dd < v l ), the /rst signal is falling after a delay time t dw that is internally set at 40 s when c up = 47 nf. the zero voltage synchronization zvs circuit 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. the input pin syn is an image of the mains voltage and is usually connected to the supply transformer through a resistor r zv . 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 pinis 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 r zv , the transformer, the rectifier drop voltage v f , the v cc supply load and the temperature. the stcc02 contribution to this delay can be evaluated by measuring the delay between its input voltage v tf and its output voltage v zvs . when using v f = 0.8v, r zv = 10 k ? , v cc = 15v, i cc = 20 ma, it is about 50 s on rising voltage v tf and 115 s on falling volt- age v tf . v cc v dd zvs v zvs v tf com 100 k ? 500 ? 25 k ? syn 20 s filter r zv ac line q s 2 s 1 50s 115s 50s 50s 115s 115s r zv cc cc = 10 k ; v = 15 v; i = 20 ma ? v zvs falling edge rising edge v tf 2v / div 40s / div
STCC02-BD5 4/13 the door closed detection circuit 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). the magnetron relay coil driver this robust driver interfaces a dc relay coil and an mcu output. the relay coil power is rated up to 1.2 w for v cc = 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 mag 2 . the diode is connected between the output pin mag 2 and the door switch pin ds. to enhance safety rules and to prevent any unventilated operation of the magnetron, the relay coil mag- netization is enabled by the fan conduction state that becomes a logic signal fan 1 \. 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 v cc to switch off these heating loads. the boolean rule of the magnetron relay operation becomes: (magnetron relay on) = ds.in 2 .fan 1 \. v cc v dd c dd ds door switch emi filter 500 ? v dd 100 k ? 50 k ? v dd mag 2 in 2 fan 1 ds demagnetizing diode relay transistor 15 k ?
STCC02-BD5 5/13 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 v cc =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 fan 1 . the diode is connected between the output pin fan 1 and the supply pin v cc . 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 v cc supply to produce the right sound level from the buzzer. the output stage is made of a transistor and a 5 k ? resistor. the transistor is referred to the power ground com and is connected by its collector to the output buz 3 . it has a dc current rating of 10 ma and runs up to 5 khz. finally, the resistor is connected between the buz 3 and v cc pins to discharge the capaci- tance of the buzzer at turn off and in off state. v cc v cc v dd v dd buz 3 fan 1 in 3 in 1 relay transistor buzzer transistor demagnetizing diode 50 k ? 15 k ? 5 k ?
STCC02-BD5 6/13 table 2: absolute ratings (limiting values) note 1: refer to the application recommendations for th e calcultation of the functional dissipation. table 3: electromagnetic compatibility ratings (t j = 25c, according to typical application diagram of page 1, unless otherwise specified) table 4: thermal resistance symbol pin parameter name & conditions value unit v dd v dd output supply voltage - 0.3 to 6 v v in v in input supply voltage - 0.3 to 30 v v ds , v cc ds, v cc door switch and power supply voltage - 0.3 to 30 v v syn syn ac input voltage, r zv = 10k ? - 1 to 30 v v mo buz 1 , mag 2 , fan 1 output voltage - 0.3 to 30 v v i in 1 , in 2 , in 3 input logic voltage - 0.3 to v dd + 0.3v v v o zvs, cdd, /rst output logic voltage - 0.3 to v dd + 0.3v v i m ds, v cc maximum sourced current pulse, tp = 10ms 120 ma mag 2 , fan 1 maximum sunk driver current pulse, tp = 1ms 120 ma maximum dc sourced current 100 ma buz 3 maximum driver diode reverse current 15 ma maximum dc sourced current 10 ma mag 2 , fan 1 maximum demagnetization diode reverse current 1 ma f max in 3 , buz 3 maximum buzzer frequency 5 khz p dis all operating dissipation, dil-16 package (1) 0.65 w t amb aii operating ambient temperature, dil-16 - 10 to 85 c t j all operating junction temperature - 10 to 150 c storage junction temperature - 25 to 150 c symbol node parameter name & conditions value unit v esd all pins esd protection, mil-std 883 method 3015, hbm model 2 kv symbol parameter value unit r th(j-a) dil-16 thermal resistance junction to ambient copper thickness = 35 m 100 c/w
STCC02-BD5 7/13 table 5: tentative electrical characteristics (t j = 25c, v cc = 12v, unless otherwise specified) symbol pin name conditions min. typ max. unit voltage supply v dd v dd output voltage supply i dd = 5 to 20ma t amb = - 10 to 85c v in = 7 to 27v c dd = 10 f 4.5 5 5.5 v v in v in input supply voltage 7 27 v i sq v in quiescent supply current v dd = 5v, i dd = 0 (open) 1.25 2.5 ma i sm v in internal circuit current (i in - i ds ) v in1 = v in2 = v in3 = v dd i dd = 20 ma 1.9 3 ma i in_sc v in limiting input current v dd = 0v output in short circuit 45 90 ma reset circuit v h /rst disabling reset threshold 4.25 4.5 v v l enabling reset threshold 3.3 3.75 v v hys threshold hysteresis 0.3 0.5 v t up disabling reset delay time c up = 47nf 1 6 ms t dw enabling reset daly time c up = 47nf 45 s zero voltage synchronization circuit t d syn zvs transition filtering time v tf = 0 to v cc rising and falling step 10 30 70 s v th syn transition threshold 0.4 0.6 0.9 v i syn syn input activating current r zv = 10k ? ,v syn = 24v 0.8 2 ma door closed detection circuit v ds h ds closed door detection 7 27 v v ds l open door detection 0.8 v i ds internal input current v ds = 27v 230 800 a door closed detection, zero volt age synchronization, reset circuits v oh cdd /rst zvs high level output voltage 0.8 v dd v v ol low level output voltage 0.2 v dd v fan relay coil driver i in1 in 1 input activating current v in1 = v dd 300 800 a v on fan 1 on state output voltage i on = 100ma, v in1 > 3.5v 1 1.5 v v fan1 h off state output voltahe v in1 < 1v, r l = 110 ? 0.9 v cc v cc v magnetron relay coil driver i in2 in 2 input activating current v in2 = v dd , v fan1 < 1.5v 300 800 a v on mag 2 on state output voltage i on = 100ma, v in2 > 3.5v v fan1 < 1.5v 1 1.5 v v mag2 h off state output voltage v in2 < 1v, r l = 110 ? 0.9 v ds v ds v buzzer driver i in3 in 3 input activating current v in3 = v dd 60 200 a f buz buzzer pwm frequency duty cycle = 50% 2 khz v buz3 h buz 3 off state output voltage v in1 0.9 v cc v cc v v on on state output voltage i on = 10ma, v in3 > 3.5v 1.2 1.8 v r buz buzzer resistance to v cc 4.7 k ?
STCC02-BD5 8/13 dc characteristics figures figure 4: regulator characteristic with t j = 25c and v in = 12v figure 5: regulator output voltage versus its junction temperature with v in = 12v figure 6: regulator output voltage versus its input voltage with i dd = 5 and 20 ma and t j = 25c 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 0 1020304050 v(v) dd i (ma) dd voltage regulation current limitation 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5 -20 0 20 40 60 80 100 120 tj (c) i =20ma dd i =5ma dd v (v) dd 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5 510152025 v (v) in v(v) dd i =20ma dd i =5ma dd
STCC02-BD5 9/13 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 dis- sipated power has to be evaluated. indeed, the stcc02 device can withstand voltages up to 30v, as specified in the "absolute ratings" section. however, when the v in voltage is high, it will also increase the power dissipation p dis and the junction temperature t j of the whole circuit. for the evaluation of the maximum junction temperature, the following equation should be used to calcu- late dissipated power: p dis = ( v in ? v dd ) i dd + v in . i q + v on ( i m@fan1 + i m@mag2 + i m@buz3 ) indeed, the power dissipation is mainly due to the regulator and to the currents sunk by the three driver outputs fan 1 , mag 2 , and buz 3 . 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 second- ary voltage. this value is then approximately 36% lower that in stand-by operation, as explained by the following equation: v in ( relays_on ) v in ( relays_off ) when the relays are off, the dissipation losses formula is: p dis = ( v in ? v dd ) i dd i q for instance if v in = 27v, v dd = 5v, i q = 2.5ma, i dd = 20ma, the dissipated power in the stcc02 is eval- uated at 0.51w. 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, v in drops down to 17.5v. considering i m buz3 = 10ma, i m fan1 = i m mag2 = 100ma and v on = 1.5v, the dissipated power in the stcc02 becomes 0.61w. the maximum junction temperature is given by: t j max = t amb max + r th ( j ? |a ) p dis 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 t amb is 85c in this application, and the thermal resistance is 100c/w, the maximum allowed dissipation becomes 0.65 w. the two dissipation cases described above are compatible with the package dissipation capability. otherwise, the ambient temperature t amb , the input voltage v in or the load current i dd should limited by design to meet the circuit thermal requirements. 2 --
STCC02-BD5 10/13 immunity improvement of stcc02 and its microcontroller 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 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 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. v dd v dd v in v in v cc door switch relay coil ds relay drive 5v reg reset rst \ rst \ com mcu stcc02 v ss 1 1 4 3 3 5 4 2 tr : 5 ns tp : 50 ns mains 0.5 kv to 4 kv burst couple
STCC02-BD5 11/13 zvs circuit compatibility with the power supply rectifier bridge in some cases, the operation of the zvs circuit may require a small capacitor c zv on the pin syn in addition to the resistor r zv . 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. open door signal immunity the door-closed signal is achieved by a high side switch connected between the vcc polarity and the ds pin. when the door switch is off and the magnetron relay coilis not supplied anymore, the low state signal is secured by the internal pull-down resistor of ds pin (50k ? ). in noisy environment with radiated interferences, t he off state of the ds signal (open door) can be reinforced by adding a resistor from ds pin to the gr ound com. its resistance can be chosen from 50 k ? to 22 k ? . d1 1n4002 vcc tr1 12v 1.5va d2~d5 1n4002 door switch c1 220uf c6 22nf mains1 r1 10k vin vcc v dd v in c up v in v cc r zv c zv dl c zvs syn in 2 in 2 com 5v regulator reset with delay zero volts sync. door closed detection magnetron driver fan driver buzzer driver 4ms/div v tf v zvs 2v/div 5v/div 4ms/div v cc v dd r ds c dd ds door switch emi filter 500 ? v dd 100 k ? 50 k ?
STCC02-BD5 12/13 figure 7: dip-16 package mechanical data i a1 b1 f e l e b b z e3 d 9 16 8 1 ref. dimensions millimeters inches min. typ. max. min. typ. max. a1 0.51 0.020 b 0.77 1.65 0.030 0.065 b 0.50 0.020 b1 0.50 0.001 d200.787 e 8.5 0.335 e 2.54 0.1 e3 17.78 0.7 f7.10.280 i5.10.201 l 3.3 0.130 z 1.27 0.050 table 6: ordering information part number marking package weight base qty delivery mode STCC02-BD5 stcc02-b dip-16 1 g 25 tube table 7: revision history date revision description of changes jun-2003 1 first issue 08-sep-2004 2 ?zero voltage synchronization zvs circuit? drawing on page 3: zvs value changed from 500k ? to 500 ? 21-oct-2004 3 minor layout update. no content change.
STCC02-BD5 13/13 information furnished is believed to be accurate and reliable. however, stmicroelectronics assu mes no responsibility for the co nsequences 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 publicati on are subject to change without notice. this publication supersedes and replac es all information previously supplied. stmicroelectronics prod ucts are not authorized for use as critical components in life support devices or systems without express written approval of stmicroelectro nics. the st logo is a registered tr ademark of stmicroelectronics. all other names are the property of their respective owners ? 2004 stmicroelectronics - all rights reserved stmicroelectronics group of companies australia - belgium - brazil - canada - china - czech republic - finland - france - germany - hong kong - india - israel - ital y - japan - malaysia - malta - morocco - singapore - spain - sweden - switzerland - united kingdom - united states of america www.st.com

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