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july 2010 doc id 15133 rev 5 1/31 31 viper27 off-line high voltage converters features 800 v avalanche rugged power section pwm operation with frequency jittering for low emi operating frequency: ? 60 khz for l type ? 115 khz for h type standby power < 50 mw at 265 vac limiting current with adjustable set point adjustable and accurate overvoltage protection on-board soft-start safe auto-restart after a fault condition hysteretic thermal shutdown application auxiliary power supply for consumer and home equipments atx auxiliary power supply low / medium power ac-dc adapters smps for set-top boxes, dvd players and recorders, white goods description the device is an off-line converter with an 800 v rugged power section, a pwm control, two levels of over-current protection, overvoltage and overload protections, hysteretic thermal protection, soft-start and safe auto-restart after any fault condition removal. burst mode operation and device very low consumption help to meet the standby energy saving regulations. advance frequency jittering reduces emi filter cost. brown-out function protects the switch mode power supply when the rectified input voltage level is below the normal minimum level specified for the system. the high voltage start-up circuit is embedded in the device. figure 1. typical topology dip-7 so 16 so16 dc inp u t high volt a ge wide r a nge - + dc o u tp u t volt a ge - + viper27 drain drain br vdd cont fb gnd table 1. device summary order codes package packaging viper27ln / VIPER27HN dip-7 tu b e viper27hd / viper27ld so16 narrow viper27hdtr / viper27ldtr tape and reel www.st.com
contents viper27 2/31 doc id 15133 rev 5 contents 1 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 typical power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4 electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1 maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.2 thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.3 electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 typical electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6 typical circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7 operation descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.1 power section and gate driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.2 high voltage startup generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7.3 power-up and soft-start up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 7.4 power down operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7.5 auto restart operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7.6 oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7.7 current mode conversion with adjustable current limit set point . . . . . . . 18 7.8 overvoltage protection (ovp) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.9 about cont pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 7.10 feed-back and overload protection (olp) . . . . . . . . . . . . . . . . . . . . . . . . 20 7.11 burst-mode operation at no load or very light load . . . . . . . . . . . . . . . . . . 23 7.12 brown-out protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.13 2nd level over current protection and hiccup mode . . . . . . . . . . . . . . . . . 25 8 package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 9 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 viper27 block diagram doc id 15133 rev 5 3/31 1 block diagram 2 typical power figure 2. block diagram vdd th er mal shutdown 6ua leb & ovp logic soft start ocp block ref tu r n -on logic drain supply & uvlo otp olp burst internal supply bus br burst-mode logic burst s r1 r2 q + - uvlo vin_ok + - ocp ref erence voltages ovp 15ua i ddch ovp vcc oscillator fb v brth hv_on otp . gnd + - rsense cont + - pwm 2nd ocp logic vdd table 2. typical power part number 230 v ac 85-265 v ac adapter (1) open frame (2) adapter (1) open frame (2) viper27 18 w 20 w 10 w 12 w 1. typical continuous power in non ventilated enclosed adapter measured at 50 c ambient. 2. maximum practical continuous pow er in an open frame design at 50 c ambient, with adequate heat sinking. pin settings viper27 4/31 doc id 15133 rev 5 3 pin settings figure 3. connection diagram (top view) note: the copper area for heat dissipation has to be designed under the drain pins. table 3. pin description pin n. name function dip7 so16n 1 1...2 gnd this pin represents the device ground and the source of the power section. -4n.a. not available for user. it can be connected to gnd (pins 1-2) or left not connected. 25vdd supply voltage of the control section. this pin also provides the charging current of the external capacitor during start-up time. 3 6 cont control pin. the following functions can be selected: 1. current limit set point adjustment. the internal set default value of the cycle-by-cycle current limit can be reduced by connecting to ground an external resistor. 2. output voltage monitoring. a voltage exceeding v ovp threshold (see table 8 on page 7 ) shuts the ic down reducing the device consumption. this function is strobed and digitally filtered for high noise immunity. 47fb control input for duty cycle control. internal current generator provides bias current for loop regulation. a voltage below the threshold v fbbm activates the burst-mode operation. a level close to the threshold v fblin means that we are approaching the cycle-by-cycle over-current set point. 58br brownout protection input with hysteresis. a voltage below the threshold v brth shuts down (not latch) the device and lowers the power consumption. device operation restarts as the voltage exceeds the threshold v brth + v brhyst . it can be connected to ground when not used. 7,8 13...16 drain high voltage drain pin. the built-in high voltage switched start-up bias current is drawn from this pin too. pins connected to the metal frame to facilitate heat dissipation. viper27 electrical data doc id 15133 rev 5 5/31 4 electrical data 4.1 maximum ratings 4.2 thermal data table 4. absolute maximum ratings symbol parameter value unit min max v drain drain-to-source (ground) voltage 800 v e av repetitive avalanche energy (limited by t j = 150 c) 5mj i ar repetitive avalanche current (limited by t j = 150 c) 1.5 a i drain pulse drain current (limited by t j = 150 c) 3 a v cont control input pin voltage (with i cont = 1 ma) -0.3 self limited v v fb feed-back voltage -0.3 5.5 v v br brown-out input pin voltage (with i br = 0.5 ma) -0.3 self limited v v dd supply voltage (i dd = 25 ma) -0.3 self limited v i dd input current 25 ma p tot power dissipation at t a < 40 c (dip-7) 1 w power dissipation at t a < 60 c (so16n) 1.5 t j operating junction temperature range -40 150 c t stg storage temperature -55 150 c table 5. thermal data symbol parameter max value unit so16n dip7 r thjp thermal resistance junction pin (dissipated power = 1 w) 25 35 c/w r thja thermal resistance junction ambient (dissipated power = 1 w) 60 100 c/w r thja thermal resistance junction ambient (1) (dissipated power = 1 w) 1. when mounted on a standard single side fr4 board with 100 mm 2 (0.155 sq in) of cu (35 m thick) 50 80 c/w electrical data viper27 6/31 doc id 15133 rev 5 4.3 electrical characteristics (t j = -25 to 125 c, v dd = 14 v (a) ; unless otherwise specified) a. adjust v dd above v ddon start-up threshold before settings to 14 v. table 6. power section symbol parameter test condition min typ max unit v bvdss break-down voltage i drain = 1 ma, v fb = gnd t j = 25 c 800 v i off off state drain current v drain = max rating, v fb = gnd 60 a r ds(on) drain-source on state resistance i drain = 0.4 a, v fb = 3 v, v br = gnd, t j = 25 c 7 i drain = 0.4 a, v fb = 3 v, v br = gnd, t j = 125 c 14 c oss effective (energy related) output capacitance v drain = 0 to 640 v 40 pf table 7. supply section symbol parameter test condition min typ max unit voltag e v drain _start drain-source start voltage 60 80 100 v i ddch start up charging current v drain = 120 v, v br = gnd, v fb = gnd, v dd = 4 v -2 -3 -4 ma v drain = 120 v, v br = gnd, v fb = gnd, v dd = 4 v after fault. -0.4 -0.6 -0.8 ma v dd operating voltage range after turn-on 8.5 23.5 v v ddclamp v dd clamp voltage i dd = 20 ma 23.5 v v ddon v dd start up threshold v drain = 120 v, v br = gnd, v fb = gnd 13 14 15 v v ddoff v dd under voltage shutdown threshold 7.5 8 8.5 v v dd(restart) v dd restart voltage threshold v drain = 120 v, v br = gnd, v fb = gnd 4 4.5 5 v current i dd0 operating supply current, not switching v fb = gnd, f sw = 0 khz, v br = gnd, v dd = 10 v 0.9 ma i dd1 operating supply current, switching v drain = 120 v, f sw = 60 khz 2.5 ma v drain = 120 v, f sw = 115 khz 3.5 ma i dd_fault operating supply current, with protection tripping 400 a i dd_off operating supply current with v dd < v dd_off v dd = 7 v 270 a viper27 electrical data doc id 15133 rev 5 7/31 table 8. controller section symbol parameter test condition min typ max unit feed-back pin v fbolp over load shutdown threshold 4.5 4.8 5.2 v v fblin linear dynamics upper limit 3.2 3.5 3.7 v v fbbm burst mode threshold voltage falling 0.6 v v fbbmhys burst mode hysteresis voltage rising 100 mv i fb feed-back sourced current v fb = 0.3 v -150 -200 -280 a 3.3 v < v fb < 4.8 v -3 a r fb(dyn) dynamic resistance v fb < 3.3 v 14 21 k h fb v fb / i d 26v/a cont pin vcont_l low level clamp voltage i cont = -100 a 0.5 v current limitation i dlim max drain current limitation v fb = 4 v, i cont = -10 a t j = 25 c 0.66 0.7 0.74 a t ss soft-start time 8.5 ms t on_min minimum turn on time 220 400 480 ns td propagation delay 100 ns t leb leading edge blanking 300 ns i d_bm peak drain current during burst mode v fb = 0.6 v 160 ma oscillator section f osc viper27l v dd = operating voltage range, v fb = 1 v 54 60 66 khz viper27h 103 115 127 khz fd modulation depth viper27l 4 khz viper27h 8 khz fm modulation frequency 250 hz d max maximum duty cycle 70 80 % over current protection (2 nd ocp) i dmax second over current threshold 1 a overvoltage protection v ovp overvoltage protection threshold 2.7 3 3.3 v t strobe overvoltage protection strobe time 2.2 us electrical data viper27 8/31 doc id 15133 rev 5 symbol parameter test condition min typ max unit brown out protection v brth brown out threshold voltage falling 0.41 0.45 0.49 v v brhyst voltage hysteresis above v brth voltage rising 50 mv i brhyst current hysteresis 7 12 a v brclamp clamp voltage i br = 250 a 3 v v dis brown out disable voltage 50 150 mv thermal shutdown t sd thermal shutdown temperature 150 160 c t hyst thermal shutdown hysteresis 30 c table 8. controller section (continued) viper27 electrical data doc id 15133 rev 5 9/31 figure 4. minimum turn-on time test circuit figure 5. brown out threshold test circuit figure 6. ovp threshold test circuit note: adjust v dd above v ddon start-up threshold before settings to 14 v 14 v 3 .5 v 50 30 v gnd cont fb vdd drain br drain v drain i drain i dlim time time t onmin 90 % 10 % gnd cont fb vdd drain br drain 14 v 2 v 10 k 30 v i brhyst v brth +v brhyst v brth v br i br v dis i brhyst i drain time time time gnd cont fb vdd drain br drain v ovp v cont v drain 14 v 2 v 10 k 30 v time time typical electrical characteristics viper27 10/31 doc id 15133 rev 5 5 typical electrical characteristics figure 7. current limit vs t j figure 8. switching frequency vs t j figure 9. drain start voltage vs t j figure 10. hfb vs t j figure 11. brown out threshold vs t j figure 12. brown out hysteresis vs t j viper27 typical electrical characteristics doc id 15133 rev 5 11/31 figure 13. brown out hysteresis current vs t j figure 14. operating supply current (no switching) vs t j figure 15. operating supply current (switching) vs t j figure 16. current limit vs r lim figure 17. power mosfet on-resistance vs t j figure 18. power mosfet break down voltage vs t j typical electrical characteristics viper27 12/31 doc id 15133 rev 5 figure 19. thermal shutdown t j v dd i drain v ddon time v ddoff v dd(restart) t sd time time t sd - t hyst shut down after over temperature normal operation normal operation viper27 typical circuit doc id 15133 rev 5 13/31 6 typical circuit figure 20. min-features flyback application figure 21. full-features flyback application opto r5 c6 ac in r3 ac in vout d3 r1 c5 u2 r4 br c4 r6 c3 c1 d1 gnd c2 r2 d2 br cont drain source control vcc fb v dd gnd br cont drain source control vcc fb c3 c2 br vout r2 daux c5 gnd rl r3 rovp rh rlim r6 d2 u2 ac in d3 r1 c6 opto d1 c4 r5 ac in c1 r4 v dd gnd operation descriptions viper27 14/31 doc id 15133 rev 5 7 operation descriptions viper27 is a high-performance low-voltage pwm controller chip with an 800 v, avalanche rugged power section. the controller includes: the oscillator with jittering feature, the start up circuits with soft-start feature, the pwm logic, the current limit circuit with adjustable set point, the second over current circuit, the burst mode management, the brown-out circuit, the uvlo circuit, the auto-restart circuit and the thermal protection circuit. the current limit set-point is set by the cont pin. the burst mode operation guaranties high performance in the stand-by mode and helps in the energy saving norm accomplishment. all the fault protections are built in auto restart mode with very low repetition rate to prevent ic's over heating. 7.1 power section and gate driver the power section is implemented with an avalanche ruggedness n-channel mosfet, which guarantees safe operation within the specified energy rating as well as high dv/dt capability. the power section has a b vdss of 800 v min. and a typical r ds(on) of 7 at 25 c. the integrated sensefet structure allows a virtually loss-less current sensing. the gate driver is designed to supply a controlled gate current during both turn-on and turn- off in order to minimize common mode emi. under uvlo conditions an internal pull-down circuit holds the gate low in order to ensure that the power section cannot be turned on accidentally. 7.2 high voltage startup generator the hv current generator is supplied through the drain pin and it is enabled only if the input bulk capacitor voltage is higher than v drain_start threshold, 80 v dc typically. when the hv current generator is on, the i ddch current (3 ma typical value) is delivered to the capacitor on the v dd pin. in case of auto restart mode after a fault event, the i ddch current is reduced to 0.6 ma, in order to have a slow duty cycle during the restart phase. viper27 operation descriptions doc id 15133 rev 5 15/31 7.3 power-up and soft-start up if the input voltage rises up till the device start threshold, v drain_start , the v dd voltage begins to grow due to the i ddch current (see table 7 on page 6 ) coming from the internal high voltage start up circuit. if the v dd voltage reaches v ddon threshold (see ta b l e 7 o n page 6 ) the power mosfet starts switching and the hv current generator is turned off. see figure 23 on page 16 . the ic is powered by the energy stored in the capacitor on the vdd pin, c vdd , until when the self-supply circuit (typically an auxiliary winding of the transformer and a steering diode) develops a voltage high enough to sustain the operation. c vdd capacitor must be sized enough to avoid fast discharge and keep the needed voltage value higher than v ddoff threshold. in fact, a too low capacitance value could terminate the switching operation before the controller receives any energy from the auxiliary winding. the following formula can be used for the v dd capacitor calculation: equation 1 the t ssaux is the time needed for the steady state of the auxiliary voltage. this time is estimated by applicator according to the output stage configurations (transformer, output capacitances, etc.). during the converter start up time, the drain current limitation is progressively increased to the maximum value. in this way the stress on the secondary diode is considerably reduced. it also helps to prevent transformer saturation. the soft-start time lasts 8.5 ms and the feature is implemented for every attempt of start up converter or after a fault. figure 22. i dd current during start-up and burst mode c vdd i ddch t ssaux v ddon v ddoff ? ---------------------------------------- = burst mode normal mode start- up normal mode i ddch (-3 ma) i dd1 i dd0 i dd v fbbm v fb v drain v fbbmhys v fblin v fbolp v dd v ddoff v ddon t t t t operation descriptions viper27 16/31 doc id 15133 rev 5 figure 23. timing diagram: normal power-up and power-down sequences figure 24. soft-start: timing diagram i dd v dd v drain v ddon time v in v drain_start power-on power-off normal operation regulation is lost here v in < v drain_start hv startup is no more activated v ddoff v dd(restart) i ddch (3ma) time time time t ss ( soft start- up ) steady state v fb v fblin v fbolp i drain i dlim v out delay (olp) t t t viper27 operation descriptions doc id 15133 rev 5 17/31 7.4 power down operation at converter power down, the system loses regulation as soon as the input voltage is so low that the peak current limitation is reached. the v dd voltage drops and when it falls below the v ddoff threshold (see table 7 on page 6 ) the power mosfet is switched off, the energy transfers to the ic interrupted and consequently the v dd voltages decreases, figure 23 on page 16 . later, if the v in is lower than v drain_start (see table 7 on page 6 ), the start up sequence is inhibited and the power down completed. this feature is useful to prevent converter?s restart attempts and ensures monotonic output voltage decay during the system power down. 7.5 auto restart operation if after a converter power down, the v in is higher than v drain_start, the start up sequence is not inhibited and will be activated only when the v dd voltage drops down the v dd(restart) threshold (see table 7 on page 6 ). this means that the hv start up current generator restarts the v dd capacitor charging only when the v dd voltage drops below v dd(restart) . the scenario above described is for instance a power down because of a fault condition. after a fault condition, the charging current, i ddch , is 0.6 ma (typ.) instead of the 3 ma (typ.) of a normal start up converter phase. this feature together with the low v dd(restart) threshold ensures that, after a fault, the restart attempts of the ic has a very long repetition rate and the converter works safely with extremely low power throughput. the figure 25 shows the ic behavioral after a short circuit event. figure 25. timing diagram: behavior after short circuit 7.6 oscillator the switching frequency is internally fixed to 60 khz or 115 khz. in both case the switching frequency is modulated by approximately 4 khz (60 khz version) or 8 khz (115 khz version) at 250 hz (typical) rate, so that the resulting spread-spectrum action distributes the energy of each harmonic of the switching frequency over a number of side- band harmonics having the same energy on the whole but smaller amplitudes. 6 $ 2 ! ) . 6 k r u w f l u f x l w r f f x u v k h u h w w w w 7 u h s 7 u h s w 6 & |