unisonic technologies co., ltd us3706 preliminary cmos ic www.unisonic.com.tw 1 of 8 copyright ? 2015 unisonic technologies co., ltd qw-r129-001.b current mode pwm power switch ? description the utc us3706 combines a dedicated current mode pwm controller with a high voltage power mosfet. low v dd startup current make the power reliable on startup design and a large value resistor could be used in t he startup circuit to minimize the standby power. at no load c ondition, the ic operates in power-saving mode for lower standby power, decreasing frequency for higher conversion efficiency at light load condition. the utc us3706 offers complete protection coverage with automatic self-recovery feature including cycle-by-cycle current limiting (ocp), over load prot ection (olp), over temperature protection (otp), over voltage protection and v dd under voltage lockout (uvlo). the internal slope compensation improves system stability at high pwm duty cycle output. leading-edge blanking on current sense input removes the signal glitch, which offering minimal external component count in the design. excellent emi performance is achieved with utc proprietary frequency hopping technique (zl201020615247.1) together with soft driver control. audio noise is eliminated due to switch frequency more than 20khz during operation. the us3706 has such applications as: battery charger, power adaptor, set-top box power supplies, ink jet printers, open-frame smps. ? features to-220f-6 1 * utc proprietary frequency hopping technology for improved emi performance. * power-saving mode for high light-load and standby efficiency * soft start * dynamic peak current limitin g for constant output power * built-in synchronized slope compensation * olp,ovpand otp for higher security * fixed switch frequency 65khz * low start-up current * cycle-by-cycle current limiting * under voltage lockout (uvlo) * leading edge blanking on source input * few external components required ? ordering information ordering number package packing lead free halogen free US3706L-TF6-T us3706g-tf6-t to-220f-6 tube
us3706 preliminary cmos ic unisonic technologies co., ltd 2 of 8 www.unisonic.com.tw qw-r129-001.b ? marking ? pin configuration ? pin description pin no. pin name description 1 drain hv mosfet drain pin. the drain pin is connected to the primary lead of the transformer. 2 v dd supply voltage 3 source hv mosfet source pin. 4 rt connected through a ntc resistor to ground for over temperature protection. 5 fb feedback input pin. the pwm duty cycle is determined by voltage level into this pin and the current-sense signal at pin 3. 6 gnd ground ? block diagram
us3706 preliminary cmos ic unisonic technologies co., ltd 3 of 8 www.unisonic.com.tw qw-r129-001.b ? absolute maximum rating parameter symbol ratings unit v dd voltage -0.3~30 v fb input voltage -0.3~7 v source input volt age -0.3~7 v operating junction temperature t j 150 c storage temperature t stg -55~150 c lead temperature (soldering, 10secs) t l 260 c note : absolute maximum ratings are those values beyo nd which the device could be permanently damaged. absolute maximum ratings are stress ratings only and functional device oper ation is not implied. ? electrical characteristics (t a =25c , v dd =16v, r t =100k ? , unless otherwise noted) parameter symbol test conditions min typ max unit supply section start up current i str v dd = v dd ( on ) -0.1v 2.5 20 a ic operating current i op v fb =3.5v 2.4 3.0 ma v dd zener clamp current v clamp i vdd =10ma 26 27.5 29 v under-voltage lockout section start threshold voltage v dd ( on ) 12 13.5 15 v min. operating voltage v dd ( min ) 7 8 9 v control section v fb open loop voltage level v fb-open 4.9 5.1 5.3 v burst-mode out fb voltage v fb ( out ) v sense =0 1.6 v reduce-frequency end fb voltage v fb ( end ) v sense =0 2.2 v burst-mode enter fb voltage v fb ( in ) v sense =0 1.5 v switch frequency normal f sw v fb =3.5v 55 60 65 khz power-saving before enter burst mode 17 22 27 khz duty cycle d max v fb =3.5v, v sense =0 70 77 85 % frequency hopping f j ( sw ) -4 +4 % frequency v dd stability f dv v dd =12v~20v 5 % frequency temperature stability f dt t=-20~100c 10 % feedback resistor r fb 17 20 23 k ? protection section v cc over voltage protection threshold v ovp v fb =3.5v 22.5 23 24.5 v fb pin over load protection threshold v olp 4.6 4.8 5.0 v power limiting debounce time t d _p l 100 125 150 ms soft start time t ss 1 2 3 ms current limiting section peak current flat threshold voltage v cs-f v fb =4.2v, duty 60% 0.8 v peak current valley threshold voltage v cs-v v fb =4.2v, duty=0% 0.7 v lead edge blanking time t leb 350 ns rt section output current of rt pin i rt 90 100 110 ua threshold voltage for otp v th _ otp 0.9 1 1.1 v mosfet section mosfet drain-source breakdown voltage bvdss 600 v static drain to source on resistance rdson 1.5 ?
us3706 preliminary cmos ic unisonic technologies co., ltd 4 of 8 www.unisonic.com.tw qw-r129-001.b ? operation description the utc us3706 is a low power off-line smps switcher optimized for off-line flyback converter. it integrates many useful designs into one controller for low-power switch-mode power supplies. the following descriptions highlight some of t he features of the us3706 series. startup current and start up control the start-up current is only 2.5 a. low start-up current allows a start- up resistor with a high resistance and a low-wattage to supply the start-up power for the controller. for ac/dc adaptor with universal input range design, a 2.5~3m ? , 1/8w startup resistor c ould be used together with a v dd capacitor to provide a fa st startup and low power dissipation solution. power-saving mode operation the proprietary power-saving mode function provides linearly decreasing the switching frequency under light-load conditions for higher efficiency. the feedback volt age, which is sampled from the voltage feedback loop, is taken as the reference. once the feedback voltage dropped below the thresh old voltage, the switching frequency starts to decrease. this power-savin g mode function dramatically reduce s power consumption under light-load conditions. the 22khz minimum frequency control also elim inates the audio noise at any loading conditions. at zero load condition, the magnitude of power loss is in proportion to the number of switching events within a fixed period of time. reducing switching events leads to the reduction on the power loss and thus conserves the energy. the us3706 enter burst mode at standby condition to mi nimize the switching lo ss and reduces the standby power consumption. power supplies using the us3706 can easily meet even the stri ctest regulations regarding standby power consumption. switch frequency set the maximum switch frequency is fixed to 60khz. switch frequency is modulated by output power p out during ic operating. at no load or light load cond ition, most of the power dissipation in a switching mode power supply is from switching loss on the mosfet transistor, the core loss of the transformer and the loss on the snubber circuit. the magnitude of power loss is in proportion to the number of sw itching events within a fixed period of time. so lower switch frequency at lower load, which more and more improve ic?s efficiency at light load. at from no load to light load condition, the ic will operate at from burst m ode to reducing frequency mode. the relation curve between f sw and p out /p out (max) as followed fig.1. 1%~100% load @ 115 & 230 vac p out /p out (max) 10 25 40 55 70 1% 9% 30% 19% 100% 115v 230v 60 fig.1 the relation curve between f sw and relative output power p out / p out (max)
us3706 preliminary cmos ic unisonic technologies co., ltd 5 of 8 www.unisonic.com.tw qw-r129-001.b ? operation description (cont.) frequency hopping for emi improvement the frequency hopping is implemented in the ic; there are two oscillators built-in the ic. the first oscillator is to set the normal switching frequency; the switching frequency is modulated with a period signal generated by the 2nd oscillator. the relation between the first oscillator and th e 2nd oscillator as followed fig.2. so the tone energy is evenly spread out, the spread spectrum minimizes the conduction band emi and therefor e eases the system design in meeting stringent emi requirement. fig.2 frequency hopping built-in slope compensation built-in slope compensation circuit greatly improv es the close loop stabilit y at ccm and prevents the sub-harmonic oscillation. leading-edge blanking each time the power mosfet is switched on, a turn-on sp ike will inevitably occur at t he sense-resistor. to avoid premature termination of the switching pulse, a 400ns leading-edge blanking time is built in. conventional rc filtering can therefore be omitted. during this blanking period, the curr ent-limit comparator is disabled and it cannot switch off the power mosfet. under voltage lockout (uvlo) the turn-on and turn-off thresholds of the us3706 are fixed internally at v dd(on) /v dd(min) during start-up, the hold-up capacitor must be charged to v dd(on) through the start-up re sistor, so that the us3706 will be enabled. the hold-up capacitor will continue to supply v dd until power can be delivered from the auxiliary winding of the main transformer. v dd must not drop below v dd(min) during this start-up process. this uvlo hysteresis window ensures that hold-up capacitor will be adequate to supply v dd during start-up.
us3706 preliminary cmos ic unisonic technologies co., ltd 6 of 8 www.unisonic.com.tw qw-r129-001.b ? operation description (cont.) protection controls the ic takes on more protection functions such as ovp, olp and otp etc. in case of those failure occurs for continual blanking time, the power mosfet is shut down . power mosfet is reset a fter failure is eliminated. ovp the ovp will shut down the switchin g of the power mosfet whenever v dd >v ovp . the ovp event as followed fig.3. fig.3 ovp case fig.4 olp case olp olp will shut down driver when v fb > v olp for continual a blanking time. the olp event as followed fig.4. otp otp will shut down driver when the ntc resistor temperature t j >t (thr) .
us3706 preliminary cmos ic unisonic technologies co., ltd 7 of 8 www.unisonic.com.tw qw-r129-001.b ? typical application circuit gnd fb rt drain v dd source 6 5 4 1 2 3 + + l n f1 3 1 lf1 4 2 r1 r2 3 1 4 2 lf2 4 bd1 1 + 2 3 r6 r23 c1 r7 + r8 d1 4 t1 5 8 9 rm-8 r41 2 b r40 c40 d5 c41 l1 c42 c43 v out + v out gnd r42 r43 c45 r47 r46 c46 u4 cy1 1 2 3 4 u3 d3 r13 c10 + c7 u1 r20 r21 r22 rt1 r12 c5 c12 c6 c2 r45 bom reference component reference component bd1 2a_600v r6, r2 resistor, chip,1.5m, 1/4w,5%, smd1206 c2 capacitor, aluminum electrolytic,33uf/400v, 105 ,20% r7, r8 resistor, chip,180k, 1/4w,5%, smd1206 c3 capacitor, ceramic, 1000pf/1kv, npo, smd1206 r13 resistor, chip,4.7-, 1/8w,5%, smd0805 c6 capacitor, ceramic, 1nf/50v, x7r, smd0805 r18 resistor, chip,1k, 1/8w,5%, smd0805 c10 capacitor, aluminum electrolytic,10uf/50v; 105 ,20% r20, r21 resistor, chip, 1.8-, 1/4w,5%, smd1206 c7, c46 capacitor, ceramic, 0.1uf/50v, x7r, smd0805 r40 resistor, chip, 47-, 1/4w,5%, smd1206 c11 capacitor, ceramic, 68pf/50v, x7r, smd0805 r41 resistor, chip,820-, 1/10w,5%, smd0603 c43 capacitor, aluminum electrolytic, 680uf/25v, 105 ,20% r42 resistor, chip,2.2k, 1/10w,5%, smd0603 c45 capacitor, ceramic, 10nf/50v, x7r, smd0805 r43 resistor, chip,300-, 1/10w,1%, smd0603 cx1 capacitor, x2, 0.33uf/275vac, 105 ,20% r45 resistor, chip,39k, 1/10w,1%, smd0603 cy1 capacitor, y1, 1000pf/400v, 105 ,20% r47 resistor, chip,10k, 1/10w,1%, smd0603 c40 capacitor, ceramic, 100pf/200v, 20%, smd1206 t1 transformer, rm-8 d1 diode , fast recovery, 1n4007, 1.0a/1000v u1 ic, pwm controller, utc us3706, to-220f-6 d3 diode , fast re covery, bav20wg, sot-123 u4 ic, tl431 sot-23 d5 diode, mgbr20l60cg, 20a/60v,to-220 u3 ic, opto-coupler, ltv-357-t-c, smd f1 fuse, 3.15a / 250v no component c1, c41, c42, c5, r1, r2, r3, r5, r12, r22, r47 lf1, lf2 choke pcb 32mmx71mmx1.6mm
us3706 preliminary cmos ic unisonic technologies co., ltd 8 of 8 www.unisonic.com.tw qw-r129-001.b utc assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all utc products described or contained herein. utc products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. the information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice.
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