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dec, 2007 v1.1 1/11 chengdu chip-rail tech. co., ltd. http://www.chiprail.com CR6853 novel low cost green-power pwm controller with low emi technique feature low cost, pwm&pfm&crm (cycle reset mode) low start-up current (about 1.5 a) low operating current (about 1.4ma) current mode operation under voltage lockout (uvlo) built-in synchronized slope compensation built-in low emi technique programmable pwm frequency audio noise free operation leading edge blanking on sense input constant output power limiting for universal ac input range sot-23-6l sop8 and dip-8 pb-free packaging compatible with sg6848 (6849) / sg5701/sg5848/ld7535 (7550) / ob2262 (2263)/ob2278 2279 complete protection with soft clamped gate output voltage 18.0v vdd over voltage protect 34.0v cycle-by-cycle current limiting sense fault protection otp (over temperature protection) output scp (short circuit protection) output olp (over load protection) latch mode after olp&scp high-voltage cmos process with esd applications switching ac/dc adaptor battery charger open frame switching power supply standby power supplies set-top box power supplies 384x replacement general description the CR6853 is a highly integrated low cost current mode pwm controller, which is ideal for small power current mode of offline ac-dc fly-back converter applications. making use of external resistors, the ic changes the operating frequency and automatically enters the pfm/crm (cycle reset mode) under light-load/zero-load conditions. this can minimize standby power consumption and achieve power- saving functions. with a very low start-up current, the CR6853 could use a large value start-up resistor (2m ). built-in synchronized slope compensation enhances the stability of the system and avoids sub-harmonic oscillation. dynamic peak current limiting circuit minimizes output power change caused by delay time of the system over a universal ac input range. leading edge blanking circuit on current sense input could remove the signal glitch due to snubber circuit diode reverse recovery and thus greatly reduces the external component count and system cost in the design. cycle-by-cycle current limiting ensures safe operation even during short-circuit. excellent emi performance is achieved built-in soft driver and low emi technique. the CR6853 offers perfect protection like ovp(over voltage protection) olp(over load protection) scp(short circuit protection) otp sense fault protection and ocp(over current protection). the CR6853s output driver is soft clamped to maximum 18.0v to protect the power mosfet. CR6853 is offered in sot-23-6l, sot-8 and dip-8 packages. free datasheet http://
CR6853 dec, 2007 v1.1 2/11 chengdu chip-rail tech. co., ltd. http://www.chiprail.com pin assignment pin descriptions name description gnd gnd pin fb voltage feedback pin. output current of this pin could c ontrols the pwm duty cycle olp and scp. ri this pin is to program the switching frequency. by co nnecting a resistor to ground to set the switching frequency. sen current sense pin, a resistor connects to sense the mosfet current. vdd supply voltage pin. gate totem output to drive the external power mosfet. typical application free datasheet http://
CR6853 dec, 2007 v1.1 3/11 chengdu chip-rail tech. co., ltd. http://www.chiprail.com block diagram simplified internal circuit architecture absolute maximum ratings symbol parameter rating unit v dd supply voltage pin voltage 40 v i ovp vdd ovp maximal enter current 20 ma v fb input voltage to fb pin -0.3 to 6v v v sen input voltage to sen pin -0.3 to 6v v p d power dissipation 300 mw esd capability, hbm model 2500 v esd capability, machine model 250 v sot-23-6l (20s) 220 dip- 8 (10s) 260 t l lead temperature (soldering) sop-8 (10s) 230 t stg storage temperature range -55 to + 150 recommended operation condition symbol parameter min ~ max unit vdd vdd supply voltage 10~30 v ri ri pin resistor value 100 k ohm t oa operation ambient temperature -20~85 p omax maximal output power 0~80 w f pwm frequency of pwm 30~150 khz free datasheet http://
CR6853 dec, 2007 v1.1 4/11 chengdu chip-rail tech. co., ltd. http://www.chiprail.com electrical characteristics ( ta=25c unless otherwise noted, v dd = 15v ) symbol parameter conditions min. typ. max. unit supply voltage (v dd pin) i st startup current 3.0 20.0 a v fb =0v 3.0 ma v fb =3v 1.4 ma i ss operating current v fb =open 1.0 ma vdd on turn-on threshold voltage 13.0 14.0 15.0 v vdd off turn-off threshold voltage 7.8 8.8 9.8 v vdd clamp vdd clamp voltage i vdd =10ma 34.0 v vdd ais anti intermission surge vdd voltage 12.7 v t off over temperature protection 130 t restart temperature restart 100 voltage feedback (fb pin) i fb short circuit current v fb =0v 1.2 ma v fb open loop voltage v fb =open 4.8 v i fb_0d zero duty cycle fb current 1.47 ma i pfm enter pfm fb current 1.37 ma i crm enter crm fb current 1.45 ma v pfm enter pfm threshold v fb 0.51 v v crm enter crm threshold v fb 0.30 v i olp&scp enter olp&scp fb current 152 ua v olp&scp enter olp&scp fb voltage 3.7 v t olp&scp olp&scp min. delay time ri=100k 33 35 50 ms current sensing (sen pin) v th_l sen minimum voltage level ri=100k, fb=3.3v 0.70 v v th_h sen maximum voltage level ri=100k, fb=3.3v 0.80 v t pd delay to output fb=3.3v 75 ns r cs input impedance 40 k v scp sense short protect voltage 177 mv free datasheet http://
CR6853 dec, 2007 v1.1 5/11 chengdu chip-rail tech. co., ltd. http://www.chiprail.com t leb leading edge blanking time ( leb ) ri=100k 300 ns oscillator (ri pin) f osc normal frequency ri=100kohm 60 65 70 khz f pfm pfm frequency ri=100kohm 22 khz dc max_w maximum duty cycle pwm ri=100kohm 77 % dc max _ f maximum duty cycle pfm ri=100kohm 14 % f temp frequency temp. stability -30-100 5 % t blank leading-edge blanking time 300 ns f jitter frequency jitter ri=100kohm -4 4 % gate drive output (gate pin) v ol output low level v dd =16v, i o =20ma 0.8 v v oh output high level v dd =16v, i o =20ma 10 v t r1 rising time c l =500pf 123 ns t f1 falling time c l =500pf 71 ns t r2 rising time c l =1000pf 248 ns t f2 falling time c l =1000pf 116 ns t r3 rising time c l =1500pf 343 ns t f3 falling time c l =1500pf 153 ns t r4 rising time c l =2000pf 508 ns t f4 falling time c l =2000pf 209 ns vg clamp output clamp voltage vdd=20v 18.0 v low emi technique f emi low emi frequency ri=100kohm 64 hz ? f_osc frequency modulation range /base frequency ri=100kohm -3 3 % free datasheet http://
CR6853 dec, 2007 v1.1 6/11 chengdu chip-rail tech. co., ltd. http://www.chiprail.com operation description current mode compared to voltage mode control, current mode control has a current feedback loop. when the voltage of the sense resistor peak current of the primary winding reaches the internal setting value v th , the register resets and the power mosfet cuts off. so, to detect and modulate the peak current cycle-by-cycle could control the output of the power supply. the current feedback has a good linear modulation rate and a fast input and output dynamic impact, and avoid the pole that the output filter inductance brings and the two-class system descends to the one-class. so it widens the frequency range and optimizes overload protection and short circuit protection. startup current and under voltage lockout the startup current of CR6853 is set to be very low so that a large value startup resistor can be used to minimize the power loss. for ac to dc adaptor with universal input range design, a 2 m , 1/8 w startup resistor and a 10uf/25v vdd hold capacitor could be used . the turn-on and turn-off threshold of the CR6853 is designed to 12.8v/7.8v. during startup, the hold-up capacitor must be charge to 13.0v through the startup resistor. the hysteresis is implemented to prevent the shutdown from the voltage dip during startup. internal bias and osc operation a resistor connected between ri pin and gnd pin sets the internal constant current source to charge or discharge the internal fixed capacitor. the charge time and discharge time determines the internal clock speed and the switching frequency. increasing the resistance will reduce the value of the input current and reduce the switching frequency. the relationship between ri and pwm switching frequency follows the below equation within the ri allowed range. ) ( ) ( 6500 khz k ri f osc w = for example, a 100k resistor ri could generate a 13ua constant current and a 65khz pwm switching frequency. the suggested operating frequency range of CR6853 is within 30khz to 150khz. green power operation the power dissipation of switching mode power supply is very important in zero load or light load condition. the major dissipation results from conduction loss switching loss and consume of the control circuit. however, all of them relates to the switching frequency. there are many difference topologies has been implemented in different chip. the basic operation theory of all these approaches intends to reduce the switching frequency under light-load or no-load condition. the CR6853`s green power function adapts pwm pfm and crm combining modulation. when ri resistor is 100k , the pwm frequency is 65khz in medium or heavy load operation. through modifying the pulse width, the CR6853 could control output voltage. the current of fb pin increases when the load is in light condition and the internal mode controller enters pfm&pwm when the feedback current is over 1.0ma. the operation frequency of oscillator is to descend gradually. when the feedback current is over 1.40ma, the frequency of oscillator is invariable, namely 22khz. CR6853 green-power function to decrease the standby consumption of the power supply, chip-rail introduces the cycle reset mode technology (crm). if the feedback current is over 1.45ma, mode controller of the CR6853 would reset internal register all the time and cut off the gate pin. while the output voltage is lower than the set value, the register would be set, free datasheet http://
CR6853 dec, 2007 v1.1 7/11 chengdu chip-rail tech. co., ltd. http://www.chiprail.com the gate pin operate again. so the frequency of the internal osc is invariable, the register would reset some pulses so that the practical frequency is decreased at the gate pin. internal synchronized slop compensation although there are more advantages of the current mode control than conventional voltage mode control, there are still several drawbacks of peak-sensing current-mode converter, especially the open loop instability when it operates in higher than 50% of the duty-cycle. to solve this problem, the CR6853 is introduced an internal slope compensation adding voltage ramp to the current sense input voltage for pwm generation. it improves the close loop stability greatly at ccm, prevents the sub-harmonic oscillation and thus reduces the output ripple voltage. duty duty duty v max slop = = 4389 .0 33.0 slop compensation current sensing & dynamic peak limiting the current flowing by the power mosfet comes into being a voltage v sense on the sense pin cycle-by-cycle, which compares to the internal reference voltage, and controls the reverse of the internal register, limits the peak current imax of the primary of the transformer. the transformer energy is 2 2 1 max i l e = . so adjusting the r sense can set the maximal output power of the power supple. the current flowing by the power mosfet has an extra value ( d p in t l v i = d ) due to the system delay time that is from detecting the current through the sense pin to power mosfet off in the CR6853 (among these, v in is the primary winding voltage of the transformer and l p is the primary wind inductance). v in ranges from 85vac to 264vac . to guarantee the output power is a constant for universal input ac voltage, there is a dynamic peak limit circuit to compensate the system delay t that the system delay brings on. ) 264 ( 65.0 v v r v ipeak in sense max = = ) 85 ( 85.0 v v r v ipeak in sense max = = low emi technique the frequency low emi technique is introduced in the CR6853. as following figure, the internal oscillation frequency is modulated by itself. a whole surge cycle includes 8 pulses and the jittering ranges from -4% to +4%. thus, the function could minimize the electromagnetic interferer from the power supply module. frequency low emi olp&scp to protect the circuit from being damaged under the over load or short circuit condition, a smart olp&scp function is implemented in the CR6853. when short circuit or over load occurs in the output end, the feedback cycle would enhance the voltage of fb pin, while the voltage is over 4.2v or the current from fb is below 152ua, the internal detective circuit would send a signal to shut down the gate and pull down the vdd voltage, then the circuit is restart. to avoid the wrong operation when circuit starts, the delay time is set. when the ri free datasheet http://
CR6853 dec, 2007 v1.1 8/11 chengdu chip-rail tech. co., ltd. http://www.chiprail.com resistance is 100kohm, the delay time t olp&scp is between 33ms and 50ms. the relationship between ri and t olp&scp follows the below equation. ) ( 10 6 3 ) ( 10 6 2 3 & 3 ms ri t ms ri scp olp < < over temperature protection the CR6853 has a built-in temperature sensing circuit to shut down pwm output once the junction temperature exceeds 130c. while pwm output is shut down, vdd voltage will gradually drop to the uvlo voltage, and vdd voltage will gradually increase again. if the junction temperature is still higher than 130c, the pwm controller will be shut down again. this situation will continue until the temperature drops below 100c. the pwm output will then be turned back. the temperature hysteresis window for the otp circuit is 30c. sense fault detect changing the resistance of sense pin could limit the maximal peak current of power mosfet. if the sense pin is short circuit to the ground and the CR6853 is overload, the power mosfet and transformer is easy to be shattered. so, the short circuit protection is built in the CR6853. every time to start up, the circuit would detect the voltage of the sense pin when the start signal is send. if the voltage keeps lower than 177mv, the circuit would be cut off and restart in 1.2ms. but, when the switch power is cut off, there could always be a big noise on the ground, so to achieve this function, it is strongly suggested that the board on the ground of the sense pin must be attention. anti intermission surge when the power supplies change the heavy load to light load immediately, there could be tow phenomena caused by system delay. they are output voltage overshot and intermission surge. to avoid it, the anti intermission surge is built in the CR6853. if it occurs, the fb current is to increase rapidly, the gate would be cut off for a while, vdd pin voltage descends gradually. when vdd reaches 12.7v, the gate pin would operate again, which the frequency is 22khz and the max. duty cycle is 14%. leading-edge blanking (leb) each time the power mosfet is switched on, a turn-on spike will inevitably occur at the sense pin, which would disturb the internal signal from the sampling of the r sense . there is a 300ns leading edge blanking time built in to avoid the effect of the turn-on spike, and the power mosfet cannot be switched off during the moment. so that the conventional external rc filtering on sense input is no longer required. over voltage protection (ovp) there is a 25.6v over-voltage protection circuit in the CR6853 to improve the credibility and extend the life of the chip. when the vdd voltage is over 25.6v, the gate pin is to shutdown immediately and the vdd voltage is to descend rapidly. gate driver & soft clamped the CR6853 output designs a totem pole to drive a periphery power mosfet. the dead time is introduced to minimize the transfixion current during the output operating. the novel soft clamp technology is introduced to protect the periphery power mosfet from breaking down and current saturation of the zener. free datasheet http://
CR6853 dec, 2007 v1.1 9/11 chengdu chip-rail tech. co., ltd. http://www.chiprail.com package demensions dip-8l dimensions millimeters inches symbol min. typ. max. min. typ. max. a 5.334 0.210 a1 0.381 0.015 a2 3.175 3.302 3.429 0.125 0.130 0.135 b 1.524 0.060 b1 0.457 0.018 d 9.017 9.271 10.160 0.355 0.365 0.400 e 7.620 0.300 e1 6.223 6.350 6.477 0.245 0.250 0.255 e 2.540 0.100 l 2.921 3.302 3.810 0.115 0.130 0.150 eb 8.509 9.017 9.525 0.335 0.355 0.375 ? 0? 7? 15? 0? 7? 15? free datasheet http://
CR6853 dec, 2007 v1.1 10/11 chengdu chip-rail tech. co., ltd. http://www.chiprail.com sot-23-6l dimensions in millimeters dimensions in inches symbol min max min max a 0.700 1.000 0.028 0.039 a1 0.000 0.100 0.000 0.004 b 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 c 2.591 3.000 0.102 0.118 d 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 h 0.080 0.254 0.003 0.010 l 0.300 0.610 0.012 0.024 free datasheet http://
CR6853 dec, 2007 v1.1 11/11 chengdu chip-rail tech. co., ltd. http://www.chiprail.com sop-8l dimensions disclaimers millimeter inch symbol min. typ. max. min. typ. max. a 1.346 1.752 0.053 0.069 a1 0.101 0.254 0.004 0.010 b 0.406 0.016 c 0.203 0.008 d 4.648 4.978 0.183 0.196 e 3.810 3.987 0.150 0.157 e 1.016 1.270 1.524 0.040 0.050 0.060 f 0.381x45 0.015x45 h 5.791 6.197 0.228 0.244 l 0.406 1.270 0.016 0.050 ? 0 8 0 8 free datasheet http://

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