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________________________________________________________________________ http://www.union-ic.com rev.02 jun.2012 1/11 UM3500 600ma, 1.5mhz, synchronous step-down dc-dc converter UM3500 sot23-5 general description the UM3500 is a 1.5mhz constant frequency, sl ope compensated current mode pwm step-down converter. the device integrates a main switch and a synchronous rectifier for high efficiency without an external schottky diode. it is ideal for powering portable equipment that runs from a single cell lithium-ion (li+) battery. the UM3500 can supply 600ma of load current from a 2.5v to 5.5v input voltage. the output voltage can be regulated as low as 0.6v. the UM3500 can also run at 100% duty cycle for low dropout operation, extending battery life in portable system. pulse skipping mode operation at light loads provides very low output ripple voltage for noise sensitive applications. the UM3500 is available in a low profile sot23-5 package. applications features z cellular and smart phones z microprocessors and dsp core supplies z wireless and dsl modems z pdas, gps z mp3 player z portable instruments z high efficiency: up to 96% z 1.5mhz constant switching frequency z 600ma output current z integrated main switch and synchronous rectifier. no external schottky diode z 2.5v to 5.5v input voltage range z output voltage as low as 0.6v z 100% duty cycle in dropout z low quiescent current: 50a z short circuit protection z thermal fault protection z <1a shutdown current z lead free sot23-5 package pin configurations top view ww: week code UM3500 sot23-5
________________________________________________________________________ http://www.union-ic.com rev.02 jun.2012 2/11 UM3500 ordering information part number packaging type marking code shipping qty UM3500 sot23-5 lta5 3000pcs/7inch tape & reel pin description pin number symbol function 1 run regulator enables control input. drive run above 1.0v to turn on the part. drive run below 0.4v to turn it off. in shutdown, all functions are disabled drawing <1 a supply current. do not leave run floating. 2 gnd ground. 3 sw p ower switch output. it is the switch node connection to inductor. this pin connects to the drains of the internal p-ch and n-ch mosfet switches. 4 vin supply input pin. must be closely decoupled to gnd, pin 2, with a 2.2 f or greater ceramic capacitor. 5 vfb feedback input pin. connect fb to the center point of the external resistor divider. bonding option absolute maximum ratings (note 1) symbol parameter value unit v in input voltage -0.3 to +6.0 v v run ,v fb run, vfb voltages +0.3 to v in +0.3 v v sw ,v out sw, vout voltages +0.3 to v in +0.3 v i sw peak sw sink and source current 1.5 a t o operating temperature -40 to +85 c t stg storage temperature range -65 to +150 c note 1: stresses greater than those listed under maximum ratings may cause permanent damage to the device. this is a stress rating only and functional opera tion of the device at these or any other conditions above those indi cated in the operational sections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect reliability.
________________________________________________________________________ http://www.union-ic.com rev.02 jun.2012 3/11 UM3500 electrical characteristics (note 2) (v in =v run =3.6v, t a =+25 , unless otherwise noted) symbol parameter test conditions min typ max unit v in input voltage range 2.5 5.5 v i q (active) input dc supply current (active mode) v fb =3.6v, v fb =vref+5% 50 100 a i q (shutdown) input dc supply current (shutdown mode) v fb =0v, v in =4.2v 0.08 1.0 a t a = +25oc 0.5880 0.6000 0.6120 0oc t a 85oc 0.5865 0.6000 0.6135 v fb regulated feedback voltage -40oc t a 85oc 0.5850 0.6000 0.6150 v i fb vfb input bias current v fb =0.65v 30 na reference voltage line regulation 2.5v v in 5.5v, v out =v fb (r2=0) 0.11 0.40 %/v output voltage line regulation 2.5v v in 5.5v, i out =10ma 0.11 0.40 %/v output voltage load regulation 100ma i out 600ma 0.0015 %/ma i o(max ) maximum output current v in =3.6v, v out =1.8v 600 ma f oscillator frequency v fb =0.6v or v out =100% 1.2 1.5 1.8 mhz r ds(on) of p-ch mosfet v in =3.6v, i sw =100ma 0.40 0.50 ? r ds(on) r ds(on) of n-ch mosfet v in =3.6, i sw = -100ma 0.35 0.45 ? i p peak induct or current v in =3.0v, v fb =0.5v or v out =90%, duty cycle<35% 1.20 a i swl sw leakage v run =0v, v sw =0v or 5v v in =5v 0.01 1 a v h run high-level threshold -40oc t a 85oc 1.0 v v l run low-level threshold -40oc t a 85oc 0.4 v i runl run leakage current vrun=3.6v 2.0 3.5 a (max) max. efficiency v in =2.7v, v out =2.5v 90 % thermal shutdown temp 160 oc note2: 100% production test at +25oc. specifica tions over the temperature range are guaranteed by design and characterization.
________________________________________________________________________ http://www.union-ic.com rev.02 jun.2012 4/11 UM3500 block diagram typical application circuit
________________________________________________________________________ http://www.union-ic.com rev.02 jun.2012 5/11 UM3500 function description UM3500 is a monolithic switching mode step-d own dc-dc converter. it utilizes internal mosfets to achieve high efficiency and can genera te very low output voltage by using internal reference at 0.6v. it operates at a fixed switc hing frequency, and uses the slope compensated current mode architecture. this step-down dc -dc converter supplies 600ma output current at v in =3.6v with input voltage range from 2.5v to 5.5v. current mode pwm control slope compensated current mode pwm control provides stable switching and cycle by cycle current limit for excellent load and line responses. during normal operation, the internal main switch is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and turned off when the peak inductor curre nt reaches the controlled value. when the main switch is off, the synchronous rec tifier will be turned on immediately and stay on until either the inductor current starts to reverse, as indicated by the current reversal comparator, ircmp, or the beginning of the next clock cycle. pulse skipping mode operation at very light loads, the UM3500 will automati cally enter pulse skipping mode to increase efficiency, further extending battery life. in th is mode, the control loop skips pwm pulses while maintaining output in regulation, and the switchi ng frequency depends on the load condition. this is a kind of pfm mode operation. dropout operation when the input voltage decreases toward the va lue of the output voltage, the UM3500 allows the main switch to remain on for more than one sw itching cycle and increases the duty cycle (note 1) until it reaches 100%. the output voltage then is th e input voltage minus the voltage drop across the main switch and the inductor. at low input supply voltage, the r ds(on) of the p-channel mosfet increases, and the efficiency of the convert er decreases. caution must be exercised to ensure the heat dissipated not to exceed th e maximum junction temperature of the ic. note 1: the duty cycle d of a step-down converter is defined as: d=t on f osc 100% v out /v in 100% where t on is the main switch on time and f osc is the oscillator frequency (1.5mhz). maximum load current the UM3500 will operate with input supply volta ge as low as 2.5v, however, the maximum load current decreases at lower input due to large ir drop on the main switch and synchronous rectifier. the slope compensation signal reduces the peak induc tor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. conversely the current limit increases as the duty cycle decreases.
________________________________________________________________________ http://www.union-ic.com rev.02 jun.2012 6/11 UM3500 typical performance characteristics ( l1 = 2.2h, c1 = 4.7f, c3 = 10f, t a = +25c, unless otherwise noted.) 0.1 1 10 100 1000 0 10 20 30 40 50 60 70 80 90 100 efficiency vs load current efficiency(%) load current(ma) vin=2.7v vin=3.6v vin=4.2v 0.1 1 10 100 1000 0 10 20 30 40 50 60 70 80 90 100 efficiency vs load current vin=2.7v vin=3.6v vin=4.2v efficiency(%) load current(ma) 0 200 400 600 800 1000 1200 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 output voltage vs load current vin=3.6v output voltage(v) load current(ma) -50 -25 0 25 50 75 100 125 1.780 1.782 1.784 1.786 1.788 1.790 1.792 1.794 1.796 1.798 1.800 output voltage vs temperature output voltage(v) temperature( o c) vin=3.6v 0.1 1 10 100 1000 0 10 20 30 40 50 60 70 80 90 100 efficiency vs load current efficiency(%) load current(ma) vin=2.7v vin=3.6v vin=4.2v 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 1.780 1.785 1.790 1.795 1.800 1.805 1.810 1.815 1.820 i o =10ma i o =100ma i o =600ma output voltage vs supply voltage output voltage(v) supply voltage(v)
________________________________________________________________________ http://www.union-ic.com rev.02 jun.2012 7/11 UM3500 typical performance characteristics (continued) ( l1 =2.2h, c1 = 4.7f, c3 = 10f, t a = +25c, unless otherwise noted.) run current vs run voltage load transient start-up from shutdown short-circuit protection 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 irun(ua) vrun (v) vout=1.8v,i o =0ma
________________________________________________________________________ http://www.union-ic.com rev.02 jun.2012 8/11 UM3500 applications information output voltage setting the external resistor divider sets the output vol tage.the feedback resistor r1 also sets the feedback loop bandwidth with the internal compensation capacitor. choose r1 around 300k ? for optimal transient response. r2 is then given by: 1 6 . 0 1 2 ? = v v r r out inductor selection a 1h to 10h inductor with dc current rati ng at least 25% higher than the maximum load current is recommended for most applications.for be st efficiency, the inductor dc resistance shall be<200m ? . for most designs, the inductance value can be derived from the following equation: osc l in out in out f i v v v v l ? = ) ( where ? i l is the inductor ripple current. choose inducto r ripple current approximately 30% of the maximum load current, 600ma. the maximum inductor peak current is: 2 ) ( l load max l i i i + = under light load conditions below 100ma, larg er inductance is recommended for improved efficiency. input capacitor selection the input capacitor reduces the surge current draw n from the input and switching noise from the device. the input capacitor impedance at the switc hing frequency shall be less than input source impedance to prevent high frequency switching curre nt passing to the input. ceramic capacitors with x5r or x7r dielectrics are highly recomme nded because of their low esr and small temperature coefficients. for most applications, a 4.7f capacitor is sufficient. output capacitor selection the output capacitor keeps output voltage ripple small and ensures regulation loop stable. the output capacitor impedance shall be low at the switching frequency. ceramic capacitor with x5r or x7r dielectrics are recommended. the output ripple ? v out is approximately: ? ? ? ? ? ? ? ? + ? 3 8 1 ) ( c f esr l f v v v v v osc osc in out in out out
________________________________________________________________________ http://www.union-ic.com rev.02 jun.2012 9/11 UM3500 layout guidance when laying out the pc board, the following su ggestions should be taken to ensure proper operation of theUM3500. 1. the power traces, including the gnd trace, the sw trace and the vin trace should be kept short, direct and wide to allow large current flow. put enough multiply-layer pads when they need to change the trace layer. 2. connect the input capacitor c1 to the vin pin as closely as possible to get good power filter effect. 3. keep the switching node, sw, away from the sensitive fb node. 4. do not trace signal line under inductor.
________________________________________________________________________ http://www.union-ic.com rev.02 jun.2012 10/11 UM3500 package information UM3500: sot23-5 outline drawing dimensions millimeters inches symbol min max min max a 1.050 1.250 0.041 0.049 a1 0.000 0.100 0.000 0.004 a2 1.050 1.150 0.041 0.045 b 0.300 0.500 0.012 0.020 c 0.100 0.200 0.004 0.008 d 2.820 3.020 0.111 0.119 e 1.500 1.700 0.059 0.067 e1 2.650 2.950 0.104 0.116 e 0.950ref 0.037ref e1 1.800 2.000 0.071 0.079 l 0.300 0.600 0.012 0.024 0 8 0 8 land pattern notes: 1. compound dimension: 2.921.60 ; 2. unit: mm; 3. general tolerance 0.05mm unless otherwise specified; 4. the layout is just for reference. tape and reel orientation
________________________________________________________________________ http://www.union-ic.com rev.02 jun.2012 11/11 UM3500 important notice the information in this document has been ca refully reviewed and is believed to be accurate. nonetheless, this document is subjec t to change without notice. union assumes no responsibility for any inaccuracies that may be contained in this document, and makes no commitment to update or to keep current the contained information, or to notify a person or organization of any update. union rese rves the right to make changes, at any time, in order to improve reliability, function or design and to attempt to supply the best product possible. union semiconductor, inc add: 2f, no. 3, lane 647 songtao road, shanghai 201203 tel: 021-51093966 fax: 021-51026018 website: www.union-ic.com

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