SD6854_datesheet primary side control smps with built-in mosfet description SD6854 is a primary side control smps with built-in mosfet. it features programmable cable drop compensation function, pfm technology and cv/cc control loop with high reliability and average efficiency. with SD6854, opto-couple and y capacitor, secondary feedback control, loop compensation circuit can be eliminated for reducing cost. in a certain output voltage range, output voltage can be set through feedback resistor, and output current also can be set through peak current sense resistor. setting cable drop compensation and peak current compensation are also available for optimized output voltage/current regulation. features * built-in high voltage mosfet * primary side control * low start-up current * leading edge blanking * pulse-frequency modulation(pfm) * overvoltage protection * undervoltage lockout * over temperature protection * cycle by cycle current limiting * open loop protection * cable drop compensation * peak current compensation applications * mobile charger * adaptor with small power * charger for mp3 and other portable apparatus * stand-by power supply ordering information part no. package marking material packing SD6854 dip-8a-300-2.54 SD6854 pb free tube SD6854g dip-8a-300-2.54 SD6854g pb free tube hangzhou silan microelectronics co.,ltd rev:0.4 2011.02.11 http://www.silan.com.cn page 1 of 9
SD6854_datesheet block diagram hangzhou silan microelectronics co.,ltd rev:0.4 2011.02.11 http://www.silan.com.cn page 2 of 9 pin configuration pin description pin no. pin name i/o function description 1 isen i peak current sense pin 2 gnd - ground 3 vcc - power supply 4 fb i feedback voltage input pin 5 cdc i cable drop compensation resistor connect pin 6 pcc i peak current compensation resistor connect pin 7 -- -- no pin 8 drain o drain pin of high voltage mosfet fb vcc osc drv over voltage protection open loop protection over temperature protection 50mv 2.1v cv control tcv s r q on control cc control t cc pcc pcc cdc reference voltage bias current uvlo cdc err amp. leb
SD6854_datesheet hangzhou silan microelectronics co.,ltd rev:0.4 2011.02.11 http://www.silan.com.cn page 3 of 9 absolute maximum rating ( unless otherwise specified, t amb =25 c ) characteristics symbol rating unit supply voltage v cc -0.3~23 v internal voltage reference v ref5v -0.3~5.5 v input voltage on pin fb v fb -20~18 v input voltage on other pins v in -0.3~ 5.3 v input current i in -10~10 ma operating junction temperature t j +160 c operating temperature range t amb -20~ +85 c storage temperature range t stg -40~+125 c esd(body mode) esd 2500 v mosfet electrical characteristics ( unless otherwise specified, t amb =25 c ) characteristics symbol test conditions min. typ. max. unit drain-source breakdown voltage b vdss v gs =0v, i d =50 a 650 -- -- v static drain-source on-state resistance r ds(on) v gs =10v, i d =0.5a -- 3.4 4.0 input capacitance c iss -- 320 -- output capacitance c oss -- 41 -- reverse transfer capacitance c rss v gs =0v, v ds =25v, f=1mhz -- 0.55 -- pf turn-on delay time t d(on) -- 12.6 -- rise time t r -- 31 -- turn-off delay time t d(off) -- 17.6 -- fall time t f v ds =0.5b vdss , i d =25ma -- 20 -- ns electrical characteristics ( unless otherwise specified, v cc =18v, t amb =25 c) characteristics symbol test conditions min. typ. max. unit supply voltage start-up current i st v cc =14v -- 3 10 a quiescent current i op 300 450 a start threshold voltage v st 13 14.5 16 v shutdown threshold voltage v sp 5.5 6.5 7.5 v reference power supply v ref5v 4.75 5.0 5.25 v feedback enable turn on voltage v en 20 50 80 mv over voltage protection v ovp 4.8 5.0 5.2 v loop open voltage v blank -1.2 -1 -0.8 v
SD6854_datesheet hangzhou silan microelectronics co.,ltd rev:0.4 2011.02.11 http://www.silan.com.cn page 4 of 9 characteristics symbol test conditions min. typ. max. unit constant voltage threshold value v cv 2.0 2.1 2.2 v dynamitic characteristic leading-edge blanking time t leb 0.3 0.6 0.9 s t cvmin 1.0 2.8 s cv loop control off time t cvmax v fb > v cv +0.2v 12 18 24 ms maximum duty of constant- voltage loop d smax 50 57 64 % pfm frequency range f s 100 200k hz over voltage recover time t ovp 12 18 24 ms current limit peak current detecting threshold voltage v pk i pcc =0 500 700 900 mv peak current compensation ? i pk i pcc =-1a 2.2 2.5 2.8 ma cable drop compensation cable drop compensation voltage v cdc r cdc =100k d s =50% 180 200 220 mv over temperature protection over temperature detection t sd 125 140 -- q c over temperature hysteresis t sdhys 20 35 50 q c function description SD6854 is controller designed for off-line smps. it features built-in mosfet, cable drop compensation and peak current compensation. cv/cc is obtained through output voltage/current controlled through detecting feedback voltage of auxiliary winding and peak current of primary winding. the whole operating period consists of peak current detection and feedback voltage detection. when mosfet is on, primary current is detected by s ense resistor and voltage at pin fb is negative, load is powered by output capacitor and output voltage v o decreases. when primary current exceeds the limit, mosfet is off and voltage at pin fb is detected. output capacitor and load are powered by secondary current and v o increases. transistor is on again after stop for t cv and hold for t cc . and then, it comes to peak current detect again. 1. start-up and under voltage lockout at the beginning, the capacitor connected to pin v cc is charged via start resistor by high voltage dc bus and the circuit starts to work if voltage at v cc is 14.5v. the circuit is powered by start resistor and auxiliary winding for normal operation. the whole control circuit enters undervoltage lockout if v cc is decreased to 6.5v, capacitor connected to pin v cc is charged through start resistor and ic only restarts when v cc =14.5v.
SD6854_datesheet 2. peak current detection when v drive 1, mosfet is on, the linearly increased primary current is detected by the sense resistor. when this current increases to the threshold value (peak value), the mosfet is off and the driving voltage v drive 0. there is a burr when mosfet is on, and mosfet will be off by error if its voltage is up to the threshold value v pk for the peak current. so the leading edge blanking time t leb 0.6 s is set to avoid this error. 3. peak current compensation the detected peak current value will be increased following the input ac voltage due to the off delay. and the output current is deeply affected by the peak current, hence the voltage regulation is worse without peak current compensation. peak current compensation is available in SD6854 through pin pcc by ac input voltage detecting. with the compensation, the detected peak current is hold with different input ac voltages for better line regulation. the threshold value v pk 0.7v is set by the circuit, that is, this value can be adjusted by r sen . the peak current compensation ability is decided by r pcc , the lower resistance, the higher compensation. hangzhou silan microelectronics co.,ltd rev:0.4 2011.02.11 http://www.silan.com.cn page 5 of 9
SD6854_datesheet 4. feedback voltage detection when mosfet is off, the voltage at pin fb is positive and voltage is sensed at 2/3 duration of this positive voltage, this sensed voltage is used for t cv control after compared with v cv , amplified and held. cv is available by t cv controlling. without consideration of voltage drop on cable and rectifier diode, the equation is shown as: cv f2 f1 f2 s1 s2 out v rr r n n v = + ? t off1 , t off2 and t on are counted at the same time which indicates durations of positive fb voltage, fb damping oscillation and fb negative voltage respectively. positive fb voltage indicates there is current delivered to the secondary side of transformer, while negative and fb damping oscillation indicate there is no current delivered to the secondary side of transformer. the duty factor is expressed as: hangzhou silan microelectronics co.,ltd rev:0.4 2011.02.11 http://www.silan.com.cn page 6 of 9 t t ttt t d off1 on off2 off1 off1 s = ++ = output current, also the average current in secondary winding: pk s off1 sp out i 2 nd t ti i = ? = 2 i sp ? peak current in secondary winding, i pk ? peak current in primary winding, n ? turns ratio of primary/secondary windings. hence, with constant peak current, when d s =d smax =0.57 (this value is determined by internal circuit), the circuit enters constant-current mode and output current is kept constant. 5. cable drop compensation in the actual design, the cable voltage drop v cab should be taken into consideration: v d is almost constant with different currents, and cable voltage drop v cab is proportional to output current, which is needed to be compensated to get better voltage regulation. for cable compensation, r cdc is used for equivalent cable resistor. and different r cdc is needed for different cable.
SD6854_datesheet 6. over voltage protection the output is shutdown if voltage at fb exceeds the threshold v ovp and this state is kept for 18ms, then the circuit restarts. 7. over temperature protection if the circuit is over temperature, the output is shut down to prevent the circuit from damage. the hysteresis of over temperature protection is used to avoid frequently change between normal and protection modes. the over protection threshold value is 140c and hysteresis value is about 35c. hence, the circuit is only normal when the temperature is 105c below. 8. open loop protection when mosfet is on, if v fb > 1v, the loop is open and open loop protection is active to shutdown the output, which keeps for 18ms and then the circuit restarts 9. pfm frequency setting pfm frequency range is determined by the constant on time t on and constant-voltage loop off time. when off time is t cvmax , the circuit works with no load and operating frequency value is minimum; when off time is t cvmin , the circuit works with full load and operating frequency value is maximum. according to the formula: fil 2 1 ivp s 2 pkm ooo ?? =?= where, lm?primary inductance, i pk ?peak current in primary side, fs?operating frequency, ?efficiency. hence, il i2v f 2 pkm oo s ? ? = hangzhou silan microelectronics co.,ltd rev:0.4 2011.02.11 http://www.silan.com.cn page 7 of 9
SD6854_datesheet typical application circuit note: the circuit and parameters are for reference only; plea se set the parameters of t he real application circuit based on the real test. package outline dip-8a-300-2.54 unit: mm hangzhou silan microelectronics co.,ltd rev:0.4 2011.02.11 http://www.silan.com.cn page 8 of 9
SD6854_datesheet mos devices operate notes: electrostatic charges may exist in many things. please ta ke following preventive measures to prevent effectively the mos electric circuit as a result of the damage which is caused by discharge: z the operator must put on wrist strap which should be earthed to against electrostatic. z equipment cases should be earthed. ? z all tools used during assembly, including soldering tools and solder baths, must be earthed. z mos devices should be packed in antistatic/conductive containers for transportation. disclaimer : x silan reserves the right to make changes to the information herein for the improvement of the design and performance without further notice! customers should obtain the latest relevant information before placing orders and should verify that such information is complete and current. x all semiconductor products malf unction or fail with some probability under special conditions. when using silan products in system design or co mplete machine manufactu ring, it is the responsibility of the buyer to comply with the safety standards strictly and take essential measures to avoid situations in which a malfunction or failure of such silan products could cause loss of body injury or damage to property. x silan will supply the best possible product for customers! hangzhou silan microelectronics co.,ltd rev:0.4 2011.02.11 http://www.silan.com.cn page 9 of 9
|
