e c 3201s 1 a, 1.5m hz, synchronous step down dc/dc converter e - cmos corp. (ww w .e c mo s . c om.tw) 5 e12 n - rev. f001 1 / 9 .. general description EC3201S is a high efficiency step down dc/dc converter operated with current mode and constant frequency. the internal switch and synchronous rectifier are integrated for high efficiency. external schottky diodes are not required. t he supply current is only 110a during operation and drops to les s than 1a in shutdown. EC3201S can supply 1a of load current from 2.5v to 5.5v supply voltage. the switching frequency is set at 1.5mhz, allowing the use of small surface mount inductors and capacitors. it can run 100% duty cyc le for low dropout application. the output voltage of EC3201S is adjustable from the fb pin. EC3201S is rohs compliant and lead (pb) free. features ? 1 a output current ? current mode operation ? high efficiency up to 9 5 % ? shu tdown current < 1a ? 2. 5 v to 5.5 v supply voltage ? over temperature protection ? constant frequency operation ? full duty ratio, 0 C 100% in dropout ? rohs compliant and lead (pb) free applications ? cellular phones ? pdas and smart phones ? mp3 players ? digital still c ameras ? slim - type dvd ? wireless and dsl card ? microprocessors and dsp core supplies ? portable instruments pin assignments 1 2 3 5 4 f b s w g n d e n v i n t o p v i e w t s o t 2 3 - 5 l g n d e n s w t o p v i e w t d f n 2 x 2 - 6 l n c v i n f b 1 2 3 6 5 4
e c 3201s 1 a, 1.5m hz, synchronous step down dc/dc converter e - cmos corp. (ww w .e c mo s . c om.tw) 5 e12 n - rev. f001 2 / 9 pin description tsot23 - 5l tdfn 2x2 - 6l symbol description 1 2 en en able control input pin. 2 5 gnd ground pin. 3 4 sw power switch output. 4 3 vin main supply pin. --- 1 nc no connected. 5 6 fb feedback pin. vout=0.6(1+r1/r2). add optional c1 to speed up transient response. typical application circuit , adjustable output voltage vout = v fb (1 + r1/r2) with r1 = 300k for typical application, and c1 should be in the range between 10pf and 47pf for component selection. ordering information part number package marking marking information ec320 1snt2r tsot23 - 5l 06l dd 1. l
e c 3201s 1 a, 1.5m hz, synchronous step down dc/dc converter e - cmos corp. (ww w .e c mo s . c om.tw) 5 e12 n - rev. f001 3 / 9 absolute maximum ratings (note 1) vin to gnd C 0.3v to +6v sw voltage to gnd ... C 0.3v to vin+0.3v en voltage to gnd .. C 0.3v to vin fb/vout to gnd .. C 0.3v to vin sw peak current .. 3a operating temperature range ... C 40c to +85c junction temperature ........... +150c storage temperature range ... C 65c to +150c lead temperature (soldering 10s) .... +260c esd classification class 2 caution: stresses above those listed in absolute maximum ratings may cause permanent damage to the device. this is a stress only rating and operation of the device at these or any other condi tions above those indicated in the operational sections of this specification is not implied. package thermal characteristics (note 2) tsot23 - 5l: thermal resistance, ja .. 250c/w thermal resistance, jc .. 130c/w tdfn 2x2 - 6l: ther mal resistance, ja ... 120c/w thermal resistance, jc .. 20c/w recommended operating conditions (note 3) supply input voltage . +2.5v to +5.5v junction temperature range C 40c to +125c ambient temperature range C 40c to +85c block diagram p w m l o g i c o s c i l l a t o r + _ + _ + _ r e f e r e n c e v i n z e r o - c u r r e n t c o m p a r a t o r d c c m 1 m 2 c u r r e n t s e n s e a m p l i f i e r u g l g s w g n d p w m c o m p a r a t o r c l o c k 0 . 6 v f b e n e r r o r a m p l i f i e r s l o p c o m p
e c 3201s 1 a, 1.5m hz, synchronous step down dc/dc converter e - cmos corp. (ww w .e c mo s . c om.tw) 5 e12 n - rev. f001 4 / 9 electrical characteristics (v in = 5v, v out = 1.8 v, l = 2.2uh, c out = 10uf, t a = 25c, unless otherwise specified) parameter symbol test conditions min typ max unit supply voltage vin 2. 5 5.5 v o utput voltage line regulation ? ? lr ? r ef for adjustable vout 0.588 0.6 0.612 v output range ( adjustable voltage) vout vin = 2.5v to 5.5v ? s v en = 0v 0.1 1 a quiesc ent current i q v en = v in , v fb = v ref 1. 1 no switching 110 a sw leakage current i leak v en = 0v, v sw = 0v or v in ? dsonp i sw = 100ma 250 m dsonn i sw = ? lim duty cycle = 100% current pulse width < 1ms 2 a oscillator frequency f osc 1.2 1. 5 1.8 mhz thermal shutdown threshold* t s 160 c en high level input voltage v enh ? 40c t a 85c enl ? 40c t a 85c en v en = 0v to vin ? * guaranteed by design not for test . note 1 : stresses beyond those listed absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional operation of t he device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions may affect device reliability. note 2 : ja is measured in the natural convec tion at ta = 25c on a low effective single layer thermal conductivity test board of jedec 51 - 3 thermal measurement standard. pin 2 of t sot23 - 5 packages is the case position for jc measurement. m easured at the exposed pad of the package. note 3: the devi ce is not guaranteed to function outside its operating conditions.
e c 3201s 1 a, 1.5m hz, synchronous step down dc/dc converter e - cmos corp. (ww w .e c mo s . c om.tw) 5 e12 n - rev. f001 5 / 9 typical characteristics startup (vin=5.0v, vout=1.8v, iload= 1 a) shutdown (vin=5.0v, vout=1.8v, iload= 1 a) vin 5v/div ven 5v/div vout 1v/div isw 1a/div 200us/div vin 5v/div ven 5v/div vout 1v/div isw 1a/div 10us/div output ripple (vin=5.0v, vout=1.8v, iload=1a) load transient (vin=5.0v, vout=1.8v, iload=0. 05a ~ 1 a) vout 10mv/div isw 1a/div 500ns/div vout 50mv/div il 1a/div 200us/div short protection/current limit (vin=5.0v, vout=1.8v, iload= 0a~ short) vout 1v/div isw 2a/div 200us/div light load efficiency curve efficiency vs. load current curve
e c 3201s 1 a, 1.5m hz, synchronous step down dc/dc converter e - cmos corp. (ww w .e c mo s . c om.tw) 5 e12 n - rev. f001 6 / 9 functional description overview the e c3201s is a constant frequency current mode pwm step down converter. EC3201S is optimized for low voltage, li - ion battery, powered applications where high efficiency and small size are critical. the device integrates both a main switch and a synchronous re ctifier, which provides high efficiency and eliminates an external schottky diode. EC3201S can achieve 100% duty cycle. the duty cycle d of a step down converter is defined as: d = t on f osc 100% 100% where t on is the main sw itch on time, f osc is the oscillator frequency (1. 5 mhz), v out is the output voltage and v in is the input voltage. current mode pwm control slope compensated current mode pwm control provides stable switching and cycle - by - cycle current limit for superior l oad and line response and protection of the internal main switch and synchronous rectifier. EC3201S switches at a constant frequency (1. 5 mhz) and regulates the output voltage. during each cycle the pwm comparator modulates the power transferred to the load by changing the inductor peak current based on the feedback error voltage. during normal operation, the main switch is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. when the main switch is off, the synchronous rectifier will be turned on immediately and stay on until either the next cycle starts or the inductor current drops to zero. the device skips pulses to improve effi ciency at light load. dropout operation EC3201S allows the main switch to remain on for more than one switching cycle and increases the duty cycle while the input voltage is dropping close to the output voltage. when the duty cycle reaches 100%, the main switch is held on continuously to deliver current to the output up to the p mosfet current limit. the output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. short circuit protection the EC3201S has short circuit protection. when the output is shorted to ground, the oscillator frequency is reduced to prevent the inductor current from increasing beyond the p mosfet current limit. the frequency will return to the normal values once the short circuit condition is removed and the vout reaches regulated voltage . maximum load current the EC3201S can operate down to 2. 5 v input voltage; however the maximum load current decreases at lower input due to large ir drop on the main switch and synchronous rectifier. the s lope compensation signal reduces the peak inductor 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. vin vout
e c 3201s 1 a, 1.5m hz, synchronous step down dc/dc converter e - cmos corp. (ww w .e c mo s . c om.tw) 5 e12 n - rev. f001 7 / 9 application i nformation inductor selection a 2.2h to 4.7h is recommended for general used. the value of inductor depends on the operating frequency. higher frequency allows smaller inductor and capacitor but increases internal switching loss. two inductor parameters should be considered, current rating and dcr. the inductor with the lowest dcr is chosen for the highest efficiency. the inductor value can be calculated as: l [v out /(f il)](1 C v out /vin) i l : inductor ripple current, which is defined as: i l = v out [(1 C v out /v in )/(l f)] (general setting) i o - max ( = 0.2~0.4) the inductor should be rated for the maximum output current (i o - max ) plus the inductor ripple current (il) to avoid saturation. the maximum inductor current (i l - max ) is given by: i l - max = i o - max + i l /2 capacitor selection the small size of ceramic capacitors are ideal for EC3201S applications. x5r and x7r types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types, suc h as y5v or z5u. a 4.7f input capacitor and a 1 0f output capacitor are su ff icient for most EC3201S applications. when selecting an output capacitor, consider the output ripple voltage and the ripple current. the esr of capacitor is a major factor to the output ripple. for the best performance, a low esr output capacitor is required. the ripple voltage is given by: v o = i l [esr + 1/(8 f c o )] output voltage programming (adjustable voltage version) the output voltage of EC3201S is set by the resistor divider according to the following formula: v out = v fb (1 + r1/r2) r1 is the upper resistor of the voltage divider. for transient response reasons, a small feed - forward capacitor (c f ) is required in parallel to the upper feedback resistor, and 22pf is recommended. checking transient response the regulator loop response can be checked by looking at the load transient response. switching regulators take several cycles to respond to a step in load current. when a load step occurs, v out will be shifted immediately by an amount equal to ( i load e sr), where e sr is the e ff ective series resistance of c out . i load will also begin to charge or discharge c out , which generates a feedback error signal. then the regulator loop will act to return v out to its ste ady state value. during this recovery time, v out can be monitored for overshoot or ringing that will indicate the stability problem. the discharged bypass capacitors are effectively put in parallel with c out , causing a rapidly drop in v out . no regulator ca n deliver enough current to prevent this problem if the load switch resistance is low and it is driven quickly. the only solution is to limit the rise time of the switch drive, so that the load rise time will be limited to approximately ( 2 5 c load ).
e c 3201s 1 a, 1.5m hz, synchronous step down dc/dc converter e - cmos corp. (ww w .e c mo s . c om.tw) 5 e12 n - rev. f001 8 / 9 package information tsot23 - 5 l symbol dimensions in mm dimensions in inch min max min max a 0.700 1. 10 0 0.0 28 0.0 43 a1 0.0 00 0.1 3 0 0.00 0 0.00 5 b 1.5 00 1. 700 0.0 59 0.06 7 b 0.300 0.5 59 0.012 0.02 2 c 2. 5 00 3.1 00 0. 098 0.1 22 d 2. 8 00 3. 100 0.11 0 0.1 22 e 0.950 bsc 0.037 bsc h 0.080 0.200 0.003 0.008 l 0. 2 00 0. 8 00 0.0 08 0.0 31 a c d b a 1 h l e b
e c 3201s 1 a, 1.5m hz, synchronous step down dc/dc converter e - cmos corp. (ww w .e c mo s . c om.tw) 5 e12 n - rev. f001 9 / 9 package information tdfn 2x2 - 6l symbols dimension (mm) dimension (inch) min nom max min nom max a 0.700 -- - 0.800 0.0 28 -- - 0.0 31 a1 0.0 00 -- - 0.050 0.00 0 -- - 0.00 2 a 3 0.175 --- 0.250 0.0 07 --- 0.0 10 b 0. 200 -- - 0. 3 5 0 0.0 08 -- - 0.0 14 d 1.950 2.000 2.050 0.0 77 0.079 0.0 81 d 2 1.000 --- 1.450 0. 039 --- 0. 057 e 1.950 2.000 2.050 0. 077 0. 079 0 . 081 e 2 0.500 --- 0.850 0.0 20 --- 0.0 33 e 0.650 0.026 l 0. 250 --- 0.400 0.01 0 --- 0.0 16 1 1 2 see detail a detail a d e d2 e2 l e b a a1 a3
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