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preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 1 general description the ap3421/a/b is a fully integrated dual output voltage regulator. the two converters are current mode and internally compensated. the converters include integrated control and synchronous rectifier switches. the outputs are both rated for up to 1a. both outputs are adjustable using external resistors. the step-down converters operate at 1.3mhz fixed switching frequency under normal load and in a pulse skipping mode for light loads. the switching clock is shifted 180 for sw2. the e/s pin provides an enable function and allows the converter to be synchronized to an external clock. with e/s held low, the ap3421/a/b draws less than 10 a current. in the start-up sequence, the vo1 output is designed to precede the vo2 output. the two outputs have controlled start-up sequence. power on reset (por) function is provided by means of an open-drain output present on the por pin. the por function monitors vmon, fb1 and fb2, and pulls low if any of these begin to drop out. the por is internally deglitched and provides a delayed recovery/reset time. the ap3421/a/b provides peak over-current protection, short circuit protection and thermal shutdown. discharge-before-turn-on discharges the outputs completely before soft-starting to always bring them up in the proper sequence at start-up or after a por (for ap3421/a only). the ap3421/a/b is available in dfn-33-10 package. features ? v o1 =1.8 to 3.6v at 1a ? v o2 =1.0 to 3.6v at 1a ? switching frequency: 1.3mhz ? 180 phase shifted switching ? no rectifier diode required ? optional external clocking (2 clock required) ? light load pulse skipping ? enable/sleep state ? internal soft-start ? open-drain power on reset monitors input and ? outputs ? discharge-before-turn-on (for ap3421/a) ? pre-bias function (for ap3421b) ? peak over current protection ? short circuit protection ? over temperature shutdown applications ? hard disk drivers ? set top boxes figure 1. package type of ap3421/a/b dfn-33-10
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 2 pin configuration dn package (dfn-33-10) pin 1 dot by m arking figure 2. pin configuratio n of ap3421/a/b (top view) pin description pin number pin name function 1 fb2 feedback from vo2. connect voltage divider to the load side of vo2 output inductor-capacitor filter 2 avin analog power input. connect a 1 f ceramic capacitor between this pin and agnd 3 pvin control mosfet switch power input. connect a 10 f ceramic capacitor between this pin and pgnd, as close to the ic as possible 4 sw2 vo2 synchronous buck switching output. connect to vo2 inductor 5 pgnd power ground connection. synchronous rectifier mosfet source. provide a star connection between this pin, vo1, vo2 filter capacitor returns, vin input capacitor return, and agnd. keep the star connection as close to the ic as possible 6 sw1 vo1 synchronous buck switching output. connect to vo1 inductor 7 e/s enable/synchronization. pulling this pin high statically enables the ic and pulling the pin low statically will shut down the ic. applying a pulse to this pin will synchronize sw1 and sw2 switching frequency to ? the external clock frequency
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 3 pin description (continued) pin number pin name function 8 por power on reset output pin. monitors fb1, fb2 output voltage levels and v in . por is pulled low if an output voltage drop is detected on fb1 or fb2 or vin, and is hi-z during normal operation 9 vmon voltage monitor?supervisor for one external voltage (could be input voltage). the por output is triggered if this output falls below the vmon threshold 10 fb1 feedback from vo1. connect voltage divider to the load side of vo1 output inductor-capacitor filter 11 agnd signal ground connection. provide a star connection between this pin and pgnd pin
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 4 functional block diagram figure 3. functional block diagram of ap3421/a/b
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 5 ordering information ap3421 - circuit type a: ap3421a b: ap3421b blank: ap3421 package dn: dfn-3 3-10 package temperature range part number marking id packing type ap3421dntr-g1 bcb ap3421adntr-g1 bdd dfn-3 3-10 -40 to 85c AP3421BDNTR-G1 bde tape & reel bcd semiconductor's pb-free products, as designated with "g1" suffix in the part number, are rohs compliant and green. absolute maximum ratings (note 1) parameter symbol value unit input voltage v in -0.3 to 7 v feedback voltage v fb -0.3 to v in +0.3 v e/s pin voltage v e/s -0.3 to v in +0.3 v sw1, sw2 pin voltage v sw v pgnd -1 to v in +1 v thermal resistance ja 33 oc /w operating junction temperature t j 150 oc storage temperature t stg -25 to 150 oc lead temperature (soldering, 10sec) t lead 260 oc note 1: stresses greater than those listed under ?absolute maximum ratings? may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under ?recommended operating co nditions? is not implied. exposure to ?absolute maximum ratings? for extended periods may affect device reliability. recommended operating conditions parameter symbol min max unit ap3421 4.5 5.5 input voltage v in ap3421a/b 3.0 5.5 v vo1 maximum output current i o1 (max) 1 a vo2 maximum output current i o2 (max) 1 a operating ambient temperature t a -40 85 c g1: green tr: tape & reel
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 6 electrical characteristics v in =v e/s =5v, t a =25 , unless otherwise specified. parameter symbol conditions min typ max unit ap3421 4.5 5.0 5.5 operating input voltage v in ap3421a/b 3.0 3.3 5.5 v supply current i cc v fb1 =v fb2 =1.2v 1.0 ma shutdown supply current i shdn v e/s =0v, v in =5.0v 10 a ap3421 3.0 3.5 4.0 under voltage lockout threshold ap3421a/b rising edge 2.4 2.7 3.0 v under voltage lockout hysteresis v huvlo 300 mv por threshold vmon v vmon_por v vmon falling 0.97 1.00 1.03 v feedback voltage v fb1, v fb2 0.975 1.0 1.025 v i lim1 1.2 1.6 switch current limit i lim2 1.2 1.6 a oscillator frequency f osc1 , f osc2 1.0 1.30 1.60 mhz soft-start time t ss_fb1 0.5 1.0 2.0 ms por threshold fb1 v fb1_por fb11falling1 86 89 92 %v fb1 por threshold fb2 v fb2_por fb21falling1 86 89 92 %v fb2 discharge complete threshold (ap3421/a ) v fb1_dct fb1 level where discharge cycle is terminated 50 75 100 mv v en_l 0.6 v e/s pin threshold v en_h 1.5 f e/s_min 1.5 frequency lock-in range f e/s_max f switching =50 % f e/s when externally clocked 3.0 mhz por assert delay time t por_delay fault flag set to por pull low 10 25 40 s por release delay time t por_hold fault flag reset to por hi-z state 10 20 30 ms por low voltage v por_low por sinking 4ma 300 mv vo2 start threshold (ap3421/a ) v fb1_st fb1 rising voltage for fb2 to initiate soft-start 86 89 92 %v fb1 sw1, sw2 discharge resistance r stop_sw1,2 discharge1resistan- ce for sw1, sw2 15 30 45 r ds_sw1_u 277 r ds_sw2_u v in =5.0v i sw =100ma 260 r ds_sw1_l 249 ap3421, ap3421a/b r ds_sw2_l v in =5.0v i sw =-100ma 160 r ds_sw1_u 300 r ds_sw2_u v in =3.3v i sw =100ma 280 r ds_sw1_l 260 internal mosfet on resistance ap3421a/b r ds_sw2_l v in =3.3v i sw =-100ma 180 m thermal shutdown threshold t otsd 160 oc thermal shutdown hysteresis t hys 10 20 30 oc
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 7 typical performance characteristics v in =v e/s =5v, v o1 =2.5v, v o2 =1.2v, l1=l2=3.3 h, c1=c3=10 f, c2=c2?=10 f, t a =25c, unless otherwise specified. figure 4. sw1, sw2 frequency vs. input voltage figure 5. supply current vs. temperature figure 6. current limit 1 vs. temperature figure 7. current limit 2 vs. temperature 3.43.63.84.04.24.44.64.85.05.25.45.65.8 200 400 600 800 1000 1200 sw1, sw2 frequency (khz) input voltage (v) -60 -40 -20 0 20 40 60 80 100 120 140 0.48 0.50 0.52 0.54 0.56 0.58 0.60 0.62 0.64 0.66 v fb1 =v fb2 =1.2v supply current (ma) temperature ( o c) -60 -40 -20 0 20 40 60 80 100 120 140 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 current limit 1 (a) temperature ( o c) -60 -40 -20 0 20 40 60 80 100 120 140 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 current limit 2 (a) temperature ( o c)
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 8 typical performance characteristics (continued) v in =v e/s =5v, v o1 =2.5v, v o2 =1.2v, l1=l2=3.3 h, c1=c3=10 f, c2=c2?=10 f, t a =25c, unless otherwise specified. figure 8. vo1 voltag e vs. output current figure 9. vo2 voltag e vs. output current figure 10. vo1 efficiency vs. output current figure 11. vo2 efficiency vs. output current 200 400 600 800 1000 1200 1400 1.000 1.025 1.050 1.075 1.100 1.125 1.150 1.175 1.200 1.225 1.250 1.275 1.300 v o1 =2.5v, i o1 =1a vo2 voltage (v) output current (ma) 200 400 600 800 1000 1200 40 45 50 55 60 65 70 75 80 85 90 95 100 vo1 efficiency (%) output current (ma) v o1 =2.5v 200 400 600 800 1000 1200 2.40 2.42 2.44 2.46 2.48 2.50 2.52 2.54 2.56 2.58 2.60 v o2 =1.2v, i o2 =1a vo1 voltage (v) output current (ma) 200 400 600 800 1000 1200 1400 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 vo2 efficiency (%) output current (ma) v o2 =1.2v
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 9 i o1 500ma/div v o1 (ac) 100mv/div i o2 500ma/div v o2 (ac) 50mv/div v in 2v/div v o1 2v/div v o2 1v/div v por 2v/div v 01 2v/div v o2 1v/div v por 5v/div v in 5v/div typical performance characteristics (continued) v in =v e/s =5v, v o1 =2.5v, v o2 =1.2v, l1=l2=3.3 h, c1=c3=10 f, c2=c2?=10 f, t a =25c, unless otherwise specified. time 4ms/div time 400 s/div figure 12. start-up from vin figure 13. power-down from vin time 100 s/div time 100 s/div figure 14. load transient figure 15. load transient (v o =2.5v i o =0.5a to 1.0a) (v o =1.2v i o =0.5a to 1.0a)
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 10 v in 5v/div output 2 induction current 20ma/div output 1 induction current 1a/div v in 2v/div output 1 induction current 1a/div v o1 2v/div v o2 2v/div v in 2v/div output 2 induction current 1a/div v o1 2v/div v o2 2v/div v in 5v/div output 2 induction current 1a/div output 1 induction current 1a/div typical performance characteristics (continued) v in =v e/s =5v, v o1 =2.5v, v o2 =1.2v, l1=l2=3.3 h, c1=c3=10 f, c2=c2?=10 f, t a =25c, unless otherwise specified. time 40 s/div time 40 s/div figure 16. short protection for output 1 figure 17. short protection for output 2 time 10ms/div time 10ms/div figure 18. output 1 short recovery figure 19. output 2 short recovery
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 11 application information 1. operation the dc-dc converters are current-mode buck converters with a synchronous rectifier and internal compensation. they are designed to be stable with a 1.5 h to 6.8 h inductor value and 10 f to 22 f output capacitor. both output voltages are resistor programmable. the switching frequency of the converter is fixed and the switches turn on at alternating 180 phase intervals. the converter operates in 2 possible modes: continuous mode (cm), and pulse skipping mode (psm). cm is the default mode under normal loading. under light loads, psm mode occurs, where switching cycles are skippe d if the current demand is low. 2. soft-start the dc-dc converter contains a soft-start function that brings the output voltages up in a slowly increasing ramp with any resistive load from open circuit to 1a (resistive) and any capacitor from 10 f to 22 f. during soft-start, the peak inductor current shall not exceed 750ma until the output voltage reaches 25% of its final valu e. current limit shall be active but not trip during soft-start into a rated resistive load. overshoot voltage during soft-start is limited to 1%. 3. power sequencing and enable when power is applied and if e/s input is asserted (high) or is toggling, the dc-dc converters will enter run mode after a short settling period. if the e/s pin is a static low, the ic will enter a sleep state where it draws very little input current. when in run mode, if there is no fault condition, the vo1 output (sw1) will be the first output to begin soft-start. when the reference voltage for fb1 reaches approximately 90% of the final value, the vo2 output (sw2) will begin soft-start. 4. por under voltage comparators are provided to monitor the output voltages and vmon which could be the input voltage. if any of these voltages falls below its por threshold, a por open drain output will turn on which pulls the por pin low. after the por condition is cleared, there is a delay of 20ms before th the por output transistor is turned off; when off the por pin is high-z and may be pulled up high with a resistor. the por function has built-in deglitching. once the por is detected, the power supply outputs will be discharged prior to restart using the soft-start/sequencing routine. 5.1over current and short circuit protection the dc-dc converters shall have over current and short circuit protection. under any load condition, at any time, any value of load resistor (including 0 ) can be applied to the dc-dc outputs instantaneously and held in place indefinitely without the switch current exceeding the peak current limit and without the ic suffering any permanent damage or loss of performance. the output voltage is allowed to drop under over current or short circuit conditions. recovery to output voltage regulation is required within 10ms of the instant the loading is reduced to maximum allowable rated load; the output voltage shall not exceed the dynamic load excursion limits ( 5% excursion) upon recovery. over current shall not be triggered by a sudden rate of load current change provided the lo ading does not exceed the output load rating of 1a. 6. e/s function enable/synchronization function. pulling this pin high statically enables the ap3421/a/b while pulling the pin low statically for longer than 4 s will shut down the ap3421/a/b. applying a pulse to this pin will synchronize sw1 and sw2 switching frequency to ? the external clock frequency. the external frequency lock-in ranges from 1.5mhz to 3.0mhz.
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 12 typical application pvin avin vmon e/s sw1 fb1 pgnd por sw2 fb2 l1 3.3 l2 3.3 agnd v in =5v c1 10 f c1' 1 f v o2 =1.2v v o1 =2.5v 84.5k 4.7k 24.9k 30.1k 20k c3 10 f c2 10 f c2' 10 f 4.02k 20k off on figure 20. typical applicati on circuit of ap3421 (note 2)
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 13 typical application (continued) pvin avin vmon e/s sw1 fb1 pgnd por sw2 fb2 l1 3.3 l2 3.3 agnd v in =3.3 to 5v c1 10 f c1' 1 f v o2 =1.2v v o1 =2.5v 36k 4.7k 18k 30.1k 20k c3 10 f c2 10 f c2' 10 f 4.02k 20k off on figure 21. typical application circuit of ap3421a /b (note 2) note 2: avin and pvin pin should not be connected together directly to avoid disturbance between them in pcb layout: 1) place a 1.0 f capacitor between avin pin and agnd for power filtering. 2) place a 10 f capacitor between pvin pin an d pgnd for power filtering.
preliminary datasheet 1.3mhz, dual 1.0a synchronous step-down converters ap3421/a/b may. 2011 rev. 1.3 bcd semiconductor manufacturing limited 14 mechanical dimensions dfn-33-10 unit: mm(inch)
important notice bcd semiconductor manufacturing limited reserves the right to make changes without further not ice to any products or specifi- cations herein. bcd semiconductor manufacturing limited does not as sume any responsibility for us e of any its products for any particular purpose, nor does bcd semiconductor manufacturi ng limited assume any liability aris ing out of the application or use of any its products or circui ts. bcd semiconductor manufacturing limited does not convey any license under its patent rights or other rights nor the rights of others. - wafer fab shanghai sim-bcd semiconductor manufacturing co., ltd. 800 yi shan road, shanghai 200233, china tel: +86-21-6485 1491, fax: +86-21-5450 0008 main site regional sales office shenzhen office shanghai sim-bcd semiconductor manuf acturing co., ltd., shenzhen office unit a room 1203, skyworth bldg., gaoxin ave.1.s., nanshan district, shenzhen, china tel: +86-755-8826 7951 fax: +86-755-8826 7865 taiwan office bcd semiconductor (taiwan) company limited 4f, 298-1, rui guang road, nei-hu district, taipei, taiwan tel: +886-2-2656 2808 fax: +886-2-2656 2806 usa office bcd semiconductor corp. 30920 huntwood ave. hayward, ca 94544, usa tel : +1-510-324-2988 fax: +1-510-324-2788 - headquarters bcd semiconductor manufacturing limited no. 1600, zi xing road, shanghai zizhu sc ience-based industrial park, 200241, china tel: +86-21-24162266, fax: +86-21-24162277 bcd semiconductor manufacturing limited important notice bcd semiconductor manufacturing limited reserves the right to make changes without further not ice to any products or specifi- cations herein. bcd semiconductor manufacturing limited does not as sume any responsibility for us e of any its products for any particular purpose, nor does bcd semiconductor manufacturi ng limited assume any liability aris ing out of the application or use of any its products or circui ts. bcd semiconductor manufacturing limited does not convey any license under its patent rights or other rights nor the rights of others. - wafer fab shanghai sim-bcd semiconductor manufacturing limited 800, yi shan road, shanghai 200233, china tel: +86-21-6485 1491, fax: +86-21-5450 0008 bcd semiconductor manufacturing limited main site regional sales office shenzhen office shanghai sim-bcd semiconductor manuf acturing co., ltd. shenzhen office advanced analog circuits (shanghai) corporation shenzhen office room e, 5f, noble center, no.1006, 3rd fuzhong road, futian district, shenzhen 518026, china tel: +86-755-8826 7951 fax: +86-755-8826 7865 taiwan office bcd semiconductor (taiwan) company limited 4f, 298-1, rui guang road, nei-hu district, taipei, taiwan tel: +886-2-2656 2808 fax: +886-2-2656 2806 usa office bcd semiconductor corporation 30920 huntwood ave. hayward, ca 94544, u.s.a tel : +1-510-324-2988 fax: +1-510-324-2788 - ic design group advanced analog circuits (shanghai) corporation 8f, zone b, 900, yi shan road, shanghai 200233, china tel: +86-21-6495 9539, fax: +86-21-6485 9673 bcd semiconductor manufacturing limited http://www.bcdsemi.com bcd semiconductor manufacturing limited

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