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application note tea5170 - secondary controller for master-slave structure AN408/1293 by t. pierre summary page i introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 ii operating principles of master-slave structure . . . . . . . . . . . . . . . . . 2 ii.1 master-slave mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 ii.2 burst mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 ii.3 operation of a master-slave supply in tv application . . . . . . . . . . . . . . 3 iii description of tea5170 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 iii.1 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 iii.2 oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 iii.2.1 operation in free-running frequency mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 iii.2.2 operation in synchronized mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 iii.3 error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 iii.4 pulse width modulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 iii.5 output stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 iii.6 v cc monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 iv tv power supply application built around tea5170 . . . . . . . . . . . . . . . . 7 iv.1 main application characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 iv.2 components external to tea5170. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 iv.3 free-running oscillation frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 iv.4 error amplifier compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 iv.5 synchronization signal matching stage . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 iv.6 soft-start period duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 iv.7 transformer characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 iv.8 operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 iv.8.1 start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 iv.8.2 stand-by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 iv.8.3 synchronized mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 iv.9 delay time in synchronized mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 iv.10 electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 v dc-dc converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 v.1 electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 v.2 operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 v.2.1 open-load protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 v.2.2 short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 v.2.3 demagnetization monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 vi conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1/12
i - introduction the tea 5170 is designed to work in the secondary part of smps, sending pulses to the slave tea2164 which is located on the primary side of the main transformer. the function of the regulation and synchronization are carried out by the tea5170. an accurate regulated voltage is obtained by duty cycle control. the tea5170 can be externally synchronized by a frequency higher or lower than the free-running frequency. this feature is particularly suitable for tv applications. ii - operating principles of master-slave structure this architecture offers two modes of operation : - master-slave mode (for normal operation) - burst mode (used during start-up and stand-by phases) ii.1 - master-slave mode in this configuration, the master circuit located on the primary side, issues pwm pulses used for output voltage regulation. these pulses are sent via a pulse tranformer to the slave circuit (figure 1). in this mode of operation, the falling edge of pwm signal may be synchronized by an external signal (e.g. by line flyback signal in tv applications). ii.2 - burst mode during start-up and stand-by phases, no regulation pulses are issued by the master circuit and thus the slave circuit operates in burst mode. in this configu- ration, the slave circuit determines the switching frequency and the burst period ( see figure 2). slave circuit master circuit sync. pulses pwm signal pulse input base current 5170-12.eps figure 1 burst period typ ? 30ms collector current envelop detail of one burst switching period 5170-13.eps figure 1 tea5170 - secondary controller for master-slave structure 2/12
ii.3 - operation of a master-slave supply in tv application the arrangement generally employed is depicted in figure 3. on the secondary side, a microcon-trol- ler is connec ted to the remote control receiver which issues control signals for stand-by and nor- mal modes of operation (figure 4). - in stand-by mode, the device power consump- tion is low (few watts). the master will no longer send any control pulses to the slave which will consequently begin operating in burst mode. - power supply regulation is performed by the slave circuit through the auxiliary winding. - in normal mode of operation, the master circuit issues the pwm signal for regulation. the power supply operates in master-slave mode. the mas- ter circuit is simultaneously synchronized with the line flyback signal. - power supply start-up. as soon as the v cc (start) threshold is reached, the slave circuit begins operating in burst mode. while the secondary voltages are being stabilized, the microcontroller holds the tv set in stand-by mode. once the start-up phase is terminated, the set may remain in stand-by mode or switch into normal mode of operation. mains input r tea2164 tea5170 c p1 voltage regulator synchronization scanning device audio output stage muting control remote stand-by remote stand-by m p v cc infra-red receiver pulse transformer pwm p1 : output voltage adjustment in normal mode p2 : output voltage adjustment in stand-by secondary ground (isolated from mains) power primary ground small signal primary ground 5170-14.eps figure 3 tea5170 - secondary controller for master-slave structure 3/12
vmonitor cc error amplifier 2v 2.7v logic (synchro) oscillator logic power output stage soft start and duty cycle l imiting pwm pwm x -1 8 7 1 5 642 3 comparator rt ct csf e- eout gnd v cc p out 5170-02.eps figure 5 : block diagram iii - description of tea 5170 the tea5170 is a fixed frequency pwm signal generator operating in voltage mode regulation. iii.1 - block diagram t t t t t v cc (start) v cc (stop) 0 0 0 t1 t2 bb b b b b 1 2 t burst t delay start-up stand-by normal operation stand-by 2 1 m p supply voltage stand-by tea5170 output voltage envelop output voltage collector current envelop tea2164 voltage v cc 5170-15.eps b : burst envelop (out of regulation) b : burst envelop (with st and-by regulation) t1, t2 : commands issued by m p t burst : burst period t delay : time constant generated by m p figure 4 tea5170 - secondary controller for master-slave structure 4/12
iii.2 - oscillator the oscillator generates a linear saw-tooth signal and sets the free-running frequency. this oscillator can also operate in synchronized mode. iii.2.1 - operation in free-running frequency mode (see figure 6) iii.2.2 - operation in synchronized mode the oscillator is synchronized by forcing the saw- tooth return. enabling the synchronized mode (figure 7) the synchronized mode is enabled when the signal pulse on pin 8 (r t ) coincides with the oscillator saw-tooth return. the "c t " capacitor charge current is then multiplied by a factor of 0.75. the tea5170 will remain in synchronized mode as long as the synchronization pulses fall within the following window : (0.8 t1 + t2) < t sync < (1.33 t1 + t2) where : -t1 : c t charge time in non synchronized mode. -t2 : c t discharge time synchronization signal (figure 8) synchronization signal is applied to pin 8 "r t " and the capacitor "c t " is discharged when voltage "v rt " exceeds the "2.7 v" threshold. comment : the internal current generator used to charge the "c t " capacitor is disabled for the entire phase where "v rt " is higher than 2v. thus, in order to maintain the saw-tooth shape of the oscillator signal, the "v rt " voltage should fall to 2v before the capacitor "c t " full discharge. 7 8 rt ct v ct current mirror 2v + v be v comp v th1 = 1v v th2 = 2v v comp v ct 2v 1v t1 = 0.5 x rt x ct t2 = 1330 x ct t ? ct (0.5 x rt + 1330) t2 t1 t : period 5170-16.eps figure 6 2v 1.6v 1v v ct rt v 2v 2.7v asynchronized mode synchronized mode synchronization window 0.8 t1 t1 1.33 t1 5170-17.eps figure 7 tea5170 - secondary controller for master-slave structure 5/12
iii.3 - error amplifier (figure 9) the on-chip error amplifier can be accessed through its inverting and output terminals. the non-inverting input is internally tied to refer- ence voltage level. v rt v ct 2.7v 5170-18.eps figure 8 comment : an internal inverting amplifier sets the correct phase polarity of the error amplifier output signal for regulation. iii.4 - pulse width modulation (figure 9) the tea 5170 is a pwm signal generator operating in voltage mode. the pulse width is determined by comparing the error signal "v om " with the oscillator saw-tooth. when the error signal "v om " exceeds the regulation range, internal threshold components will set a minimum conduction time t on (min) and also limit the maximum conduction time t on (max). at initial start-up, a soft-start function implemented by linear charge of soft-start capacitor "c (s-start) " is used to vary gradually the t on (max) threshold. the output pulse width varies from t on (min) to t on (max) nominal value for v c(s-start) voltage variation of 0 to 2v. 5 6 v om v osc pwm v pin5 v pin6 v osc v om amplifier output pwm inputs pwm output 5170-19.eps figure 9 tea5170 - secondary controller for master-slave structure 6/12
logical controller 7.7v 3 1ma 1ma 5170-20.eps figure 10 iii.5 - output stage (see figure 10) the output stage operates in on/off mode. for a supply voltage higher than 8v, the output signal value is independent of the supply voltage (typical value : 7v). iii.6 - v cc monitoring v cc rising : when v cc reaches the value "v cc (start) ", an in- ternal switch enables the operation of the output stage and the soft-start capacitor begins charging. the internal logic circuitry becomes operational before v cc has reached the "v cc (start )" value. v cc falling : when v cc falls below the "v cc (stop) " level, the negative output stage is switched-on, the transistor is turned off and the soft-start capacitor is dis- charged. iv - tv power supply application built around tea5170 (figure 15) general structure and operational features of this power supply were outlined in section 1. the details covered below apply to a power supply configuration using the slave "tea2164" device. (refer to tea2164 data sheet and application note "an409/0591" for further details) . iv.1 - main application characteristics characteristic value input voltage 170v ac to 270v ac output power 20w to 120w output power in stand-by mode 1w to 6w switching frequency 32khz synchronization on line flyback signal (positive) iv.2 - components external to tea5170 component value calculation also refer to tea2164 application note "an- 409/0591" for calculation methods applicable to other power supply elements. the external components determine the f ollowing parameters : - operating frequency -t on (min) - soft-start - error amplifier gain ideal values - period of operation "t osc " : 32 m s -t on (min) duration : 1.2 m s - soft-start duration : 20ms - error amplifier gain : dc gain g dc = 35 ac gain at 1/10 x t osc : g ac = g dc /5 = 7 iv.3 - free-running oscillation frequency for efficient use of tea5170 and tea2164 syn- chronization windows, the periods of both devices are determined as folows : t osc(5170) = t sync 1.06 t osc(2164) = t osc ( 5170 ) 1.223 where : -t sync : line flyback signal period -t osc(5170) : tea5170 free-running period -t osc(2164) : tea2164 free-running period numerical application period of synchronization signal being t sync = 32 m s : t osc(5170) =t sync 1.06 =30.2 m s t osc(2164) =t osc ( 5170 ) 1.223 = 30.2 1.223 = 24.7 m s the tea5170 free-running period is determined as follows : t osc(5170) = c t (0.5 x r t + 1330) where : c t = t on ( min ) - 0.5 10 - 6 1330 -r t = 105k w (1%) -c t = 560 pf (2%) tea5170 - secondary controller for master-slave structure 7/12
iv.4 - error amplifier compensation - a high dc gain is required for good accuracy. - for stability reasons, the ac gain must be attenu- ated so as to avoid injection of the switching frequency component into the regulation loop. - dc gain : g dc = r3 r2 + r1 r2 r1 - ac gain : g ac = r3 1 j w c r3 + 1 j w c r2 + r1 r2 r1 assumptions : - r2 > > r1 since v out >10 v ref so the value of r2 does not modify the result of calculation and only r1 and r3 influence may be taken into consideration. - r1 = 2.2k w , r3 = 75k w - with cut-off frequency in ac regulation mode : -f c = 1 10 t osc t c = 2.2nf r1 v ref r3 r2 c v out 5170-21.eps figure 11 iv.5 - synchronization signal matching stage (figure 12) the synchronization signal is generated from the line flyback. 8 rt v rt r v sync rp c eht transformer 5170-22.eps figure 12 9 3 6 7 13 14 17 20 21 22 19 5170-23.eps figure 13 the pulse amplitude is given by : v 8 ( max ) v sync = r r + r p with r t > > r the pulse time constant is (r+ r p )c and should be lower than the saw-tooth fall time. thus, for a line flyback signal amplitude of 50v : r = 6.8k w , r p = 75k w , c = 150pf comment : practical and theoretical values may differ slightly since the rise time of the line flyback s ignal is not generally negligible. iv.6 - soft-start period duration in this application, the duration of soft-start is around 20ms, with : c (s-start) = t (s-start) x 2 x 10 -6 = 47nf iv.7 - transformer characteristics (reference : g4453-02 orega) winding pin inductance n p 3-6 680 m h n aux 7-9 7 m h n2 19-13 592 m h n3 19-20 12 m h n4 14-17 5 m h n5 22-21 25 m h iv.8 - operation iv.8.1 - start-up the power supply of tea5170 begins rising gradu- ally upon initial start-up of the primary circuit. when v cc reaches the value v cc (start) = 4v, the oscil- lator has already begun running and the soft-start capacitor "c (s-start) " begins charging. the con- duction time is t on (min) and rises gradually. tea5170 - secondary controller for master-slave structure 8/12
iv.8.2 - stand-by this function is externally activated by grounding the "stand-by" input thereby disabling the power supply of tea5170. (figure 15). to return to normal mode of operation, this pin should be left floating. iv.8.3 - synchronized mode the differentiator at synchronization input will transform the line flyback signal into a rect angular pulse whose time constant is around 1ms. in this mode of operation, there is a lapse of time between the falling edge of the synchronization signal and the real transistor turn-off (figure 13). in tv applications, this time should be less than the line flyback duration so as to avoid the occurrence of on-screen visible disturbances. t1 and t3 times are specific to tea5170 (t1 + t3 = 800ns typ.) t4 is specific to the primary circuit (= 800ns typ. with tea2164). only t2 = t on (min) and t5 = t stg of the switching transistor can be modified according to individual application requirements. iv.9 - delay time in synchronized mode flyback signal oscillator voltage (tea5170) output voltage (tea5170) base current collector current i base () i c () v rt t2 t3 t4 t5 t1 2.7v 2v 5170-24.eps figure 14 tea5170 - secondary controller for master-slave structure 9/12
iv.10 - electrical diagram 1 2 3 4 5 6 7 8 9 10 16 11 12 13 14 15 tea2164 100k w 1% 2% 16v 560pf 4.7 m f 47 m f bzx85c3v0 18 w 2.2 m h sgs f344 0.24 w / 1w 100 w 5.6 w 1w 68k w p2 22k w 1nf 100nf 220 m f 25v 120k w 2w 4.7 w 2w ba157 mains 220 v ac 150 m f 385v 4 x 1n4007 470 m f 25v plr811 20 19 13 12v by218-600 100 m f 25v 1000 m f 25v by218-100 14 17 1000 m f 40v by218-100 22 21 25v bc 550c 10k w 3 6 9 7 orega g4453-02 2.2k w 120k w p1 47k w 135v 7.5v stand-by control 2 4 6 5 7 8 3 1 tea5170 75k w 1.2nf 10 m f 16v 560pf 2% 47nf 1n4148 68k w 100k w 1% 150pf sync. input 470k w 8w ba159 2.7nf 1kv 1nf/1kv 270 w puls e transformer p : 120w f : 32khz out 5170-25.eps figure 15 tea5170 - secondary controller for master-slave structure 10/12
22 m f 1 2 3 4 5 6 7 8 tea5170 120k w 470pf 220nf 220nf 68nf 180 w 1n 4148 270k w 1n4148 v in 5v to 13v by100-200 220mf 48v 47k w 3.9k w 47k w 24v 24v 50ma n p n s 5170-26.eps figure 16 v - dc-dc converter (9v 40% => 24v , 1.5w) (figure 16) this low power converter employs a transformer wound on a low-cost ferrite former. the configuration is protected against open loads and short-circuits. transformer characteristics - primary inductance : 53.5 m h - transformation ratio for 24v : n s / n p = 2 regulation characteristics - line regulation at 4.9v to 15v : 24v 0.22% - load regulation for (0.4p max - p max ) : 24v 0.12% - power range : 0.24w to 1.6w - efficiency : 40% v.1 - electrical diagram v.2 - operation - the period of operation is determined by r t and c t components. - minimum conduction duration : 0.6 m s - free-running period : 29 m s - soft-start period duration : preset at 100 ms. v.2.1 - open-load protection in case of low load values, the minimum conduction time t on (min) with respect to the period of operation is too high to maintain the output voltage at its nominal value. the only solution to stabilize the voltage is to increase the period of operation by reducing the charge current of the oscilator capaci- tor c t . this is obtained by injecting additional cur- rent into resistor r t as soon as the output voltage v out rises. v.2.2 - short-circuit protection when the current through transistor becomes sub- stantially high, the transistor is saturated and in- duces a high di c /dt . the diode on switching transistor base is then forward biased and begins deviating a portion of the base current. this phe- nomenon is self amplified and therefore results in rapid transistor turn-off. v.2.3 - demagnetization monitoring in order to avoid magnetic flux runaway, the tran- sistor should be driven into conduction only once the transformer has been fully demagnetized. while the transformer is being demagnetized, the secondary-connected rectifier diode is forward bi- ased and thus maintains the error amplifier output at 0 potential. the allowed conduction period is consequently t on (min) . tea5170 - secondary controller for master-slave structure 11/12
vi - conclusion the tea5170 requires a very simple configuration and yet offers excellent regulation quality combined with synchronization possibil ity for flyback-type converters. the tea5170 can be used in converters operating at 16khz to over 100khz frequency range. access to error amplifier and soft-start input are some of the remarkable features offered by this device whose application areas are by no means limited. the tea5170 belongs to the family of master controller devices characterized by their outstand- ing flexibility of use and application performances. information furnished is believed to be accurate and rel iable. however, sgs-thomson microelectronics 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 licence is granted by implication or otherwise under any patent or patent rights of sgs-thomson microelectronics. specifications mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. sgs-thomson microelectronics products are not authorized for use as critical components in lif e support devices or systems without express written approval of sgs-thomson microelectronics. ? 1994 sgs-thomson microelectronics - all rights reserved purchase of i 2 c components of sgs-thomson microelectronics, conveys a license under the philips i 2 c patent. rights to use these components in a i 2 c system, is granted provided that the system conforms to the i 2 c standard specifications as defined by philips. sgs-thomson microelectronics group of companies australia - brazil - china - france - germany - hong kong - it aly - ja pan - korea - malaysia - malta - morocco the netherlands - singapore - spain - sweden - switzerland - taiwan - thailand - united kingdom - u.s.a. tea5170 - secondary controller for master-slave structure 12/12

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