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wd312 1 1a output current , fixed 5v (*) output voltage, boost converter with 2.75a main - switch descriptions the wd3121 is a high efficiency, peak current control mode dc - dc boost converter. it supports up to 1a output current with an integrated low r ds(on) ( 130m ?) n - channel mosfet and cycle by cycle current limit protection . the device provides a usb 5v compliant power output from a single li - ion battery. the b oost converter run s in pulse - width modulation (pwm) mode , at 1mhz fixed switching frequency to reduce o utput ripple, improve conversion efficiency. it allows for the use of small external components. at light load currents the converter enters skipping mode to maintain a high efficiency over a wide load current range. the build - in soft start circuitry minim izes the inrush current at start - up. fixed 5v (*) output and internal compensation network require only boost inductor, schottky diode, and input and output capacitors for wd3121 , save pcb area . the wd3121 is available in sot - 23 - 6 l package. standard produc t is pb - free and halogen - free. features ? input voltage range : 2.7~5.5v ? continuous output current : 1.0a ? switch ing frequency : 1 mhz (typ.) ? efficiency : up to 92% ? m ain switch current limit : 2.75a (min.) ? low r ds(on) main switch : 0.1 3 ? fixed output voltage : 5 v (*) ? output voltage accuracy : 2% applications ? mid ? mobile power pack ? mobile phones ? notebook computers ? portable games sot - 23 - 6l pin c onfiguration (top view) **** = device code yy = year code ww = week code marking order i nformation note: * : wd3121e fixed 5v output voltage wd3121e 51 fixed 5.1v output voltage wd3121e 52 fixed 5.2v output voltage device package marking shipping wd3121 e - 6/tr sot - 23 - 6l 3121 3000/reel&tape wd3121 e 51 - 6/tr sot - 23 - 6l e5v1 3000/reel&tape wd3121 e 52 - 6/tr sot - 23 - 6l e5v2 3000/reel&tape lx en gnd nc vdd out 1 2 3 6 5 4 1 2 3 6 5 4 **** yyww 1 of 11 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification lx en gnd nc vdd out 1 2 3 6 5 4 1 2 3 6 5 4 **** yyww
typical applications block diagram pin descriptions symbol sot - 23 - 6l descriptions lx 1 switch pin gnd 2 ground out 3 c onnect to output en 4 enable , active high vdd 5 power supply nc 6 not connect osc 1 mhz ocp pwm logic gate driver current sense vref ea pwm comp soft start uvlo ce lx vdd en gnd out thermal shutdown vdd gnd lx en out l / 2 . 2 h wsb 5509 l cout 1 22 f cin 22 f v in en vout cout 2 22 f nc wd 3121 wd312 1 2 of 11 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification osc 1 mhz ocp pwm logic gate driver current sense vref ea pwm comp soft start uvlo ce lx vdd en gnd out thermal shutdown vdd gnd lx en out l / 2 . 2 h wsb 5509 l cout 1 22 f cin 22 f v in en vout cout 2 22 f nc wd 3121
absolute m aximum r ating s these are stress ratings only. stresses exceeding the range specified under absolute maximum ratings may cause substantial damage to the device. functional opera tion of this device at other conditions beyond those listed in the specification is not implied and prolonged exposure to extreme conditions may affect device reliability. note 1: surface mounted on fr - 4 board using 1 square inch pad size , dual side , 1oz copper note 2: surface mounted on fr - 4 board using minimum pad size, 1oz copper parameter sym bol value unit vdd pin voltage r ange v dd - 0.3 6.5 v out pin voltage r ange v out - 0.3 6.5 v en pin voltage range v en - 0.3 v dd v lx pin voltage range (dc) v lx - 0.3 v dd v power dissipation C sot - 23 - 6l (note 1) p d 0.5 w power dissipation C sot - 23 - 6l (note 2) 0.3 w junction to ambient thermal resistance C sot - 23 - 6l (note 1) r ja 250 o c/w junction to ambient thermal resistance C sot - 23 - 6l (note 2) 416 o c/w junction temperature t j 1 50 o c lead temperature(soldering, 10s) t l 260 o c operation temperature topr - 40 ~ 85 o c storage temperature tstg - 55 ~ 150 o c esd ratings hbm 8000 v mm 400 v wd312 1 3 of 11 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
electronics characteristics (ta=25 o c , v in =3. 7 v, v en =v in , unless otherwise noted) parameter symbol test condition min typ max units operation voltage range v dd 2.7 -- 5.5 v under voltage lockout v uvlo v in rising 1.8 2.2 2.5 v uvlo hysterisis v uvlo - hys 0.1 v quiescent current i q v out = 5.5 v 0.3 1 ma supply current i s v out = 4 .5 v 1 2 ma shutdown current i sd v en < 0.4v 1 a operation frequency f osc 0.8 1 1.2 mhz maximum duty cycle d max 85 % output voltage wd3121e v out i load =100ma 4.9 5 5.1 v wd3121e51 v out i load =100ma 5 5 .1 5. 2 v wd3121e52 v out i load =100ma 5.1 5 .2 5 .3 v main switch mos on - resistance r on_s i lx =1 00ma 0.1 3 ? main switch current limit i lim 2.75 4.2 a shutdown voltage v en l 0.4 v enable voltage v en h 1.5 v en sink current i en 3 a thermal shutdown temperature t sd 160 c t sd hysteresis t sd - hys 30 c wd312 1 4 of 11 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
typical characteristics (ta=25 o c , v in =3.7v, v en =v in , unless otherwise noted ) efficiency vs. output current output voltage vs. input voltage frequency vs. input voltage en threshold voltage vs. input voltage ou tpu t vo ltage vs. output current output voltage vs. output current 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 50 55 60 65 70 75 80 85 90 95 100 v in =4.2v v in =3.7v v in =3.2v efficiency(%) output current(a) 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.90 4.92 4.94 4.96 4.98 5.00 5.02 5.04 5.06 5.08 5.10 i load =0ma i load =100ma i load =500ma i load =1000ma output voltage(v) input voltage(v) 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 0.80 0.85 0.90 0.95 1.00 1.05 1.10 i load =500ma oscillator frequency(mhz) input voltage(v) 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 falling rising enable threshold(v) input voltage(v) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 4.90 4.92 4.94 4.96 4.98 5.00 5.02 5.04 5.06 5.08 5.10 v in =4.2v v in =3.7v v in =3.2v v in =2.7v output voltage(v) output current(a) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 4.90 4.92 4.94 4.96 4.98 5.00 5.02 5.04 5.06 5.08 5.10 t=85 0 c v in =4.2v v in =3.7v v in =3.2v v in =2.7v output voltage(v) output current(a) wd312 1 5 of 11 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 50 55 60 65 70 75 80 85 90 95 100 v in =4.2v v in =3.7v v in =3.2v efficiency(%) output current(a) 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.90 4.92 4.94 4.96 4.98 5.00 5.02 5.04 5.06 5.08 5.10 i load =0ma i load =100ma i load =500ma i load =1000ma output voltage(v) input voltage(v) 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 0.80 0.85 0.90 0.95 1.00 1.05 1.10 i load =500ma oscillator frequency(mhz) input voltage(v) 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 falling rising enable threshold(v) input voltage(v) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 4.90 4.92 4.94 4.96 4.98 5.00 5.02 5.04 5.06 5.08 5.10 v in =4.2v v in =3.7v v in =3.2v v in =2.7v output voltage(v) output current(a) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 4.90 4.92 4.94 4.96 4.98 5.00 5.02 5.04 5.06 5.08 5.10 t=85 0 c v in =4.2v v in =3.7v v in =3.2v v in =2.7v output voltage(v) output current(a)
oscillator frequency vs. temperature uvlo vs. temperature enable threshold voltage vs. temperatur e ou tput voltage vs. temperatur e -50 -25 0 25 50 75 100 125 0.95 0.96 0.97 0.98 0.99 1.00 1.01 1.02 1.03 1.04 1.05 v in =3.7v i load =500ma oscillator frequency(mhz) temperature( o c) -50 -25 0 25 50 75 100 125 0.75 0.80 0.85 0.90 0.95 1.00 1.05 rising falling enable threshold(v) temperature( o c) -50 -25 0 25 50 75 100 125 2.08 2.10 2.12 2.14 2.16 2.18 2.20 2.22 2.24 2.26 falling rising uvlo(v) temperature( o c) -50 -25 0 25 50 75 100 125 4.90 4.92 4.94 4.96 4.98 5.00 5.02 5.04 5.06 5.08 5.10 i load =1000ma i load =500ma i load =100ma i load =0ma vin=3.7v output voltage(v) temperature( o c) wd312 1 6 of 11 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification -50 -25 0 25 50 75 100 125 0.95 0.96 0.97 0.98 0.99 1.00 1.01 1.02 1.03 1.04 1.05 v in =3.7v i load =500ma oscillator frequency(mhz) temperature( o c) -50 -25 0 25 50 75 100 125 0.75 0.80 0.85 0.90 0.95 1.00 1.05 rising falling enable threshold(v) temperature( o c) -50 -25 0 25 50 75 100 125 2.08 2.10 2.12 2.14 2.16 2.18 2.20 2.22 2.24 2.26 falling rising uvlo(v) temperature( o c) -50 -25 0 25 50 75 100 125 4.90 4.92 4.94 4.96 4.98 5.00 5.02 5.04 5.06 5.08 5.10 i load =1000ma i load =500ma i load =100ma i load =0ma vin=3.7v output voltage(v) temperature( o c)
start - up from en shutdown from en load step start - up from en shutdown from en load step wd312 1 7 of 11 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
operation information norma l operation the wd3121 is a fixed 5v (*) output , peak current control led dc - dc boost converter . this means that switch duty cycle is directly controlled by the peak switch current rather than only by output voltage. the wd3121 regulates the output voltage using a combined pulse - width (pwm) and pulse - skipping (psm) modulation topology . in pwm mode, the device runs at a 1mhz fixed frequency . referring to the block diagram, the switch is turned on at the start of each oscillator cycle. it is turned off when sw itch current reaches a predetermined level. the current trip level is set by using a n error amplifier which senses the converter output voltage . the ma in switch current sensing voltage signal is summed by a slope compensation voltage signal . slope compensa tion is necessary to prevent sub - harmonic oscillations that may occur in peak current mode architectures when exceed ing 50% duty cycle. at very light loads, the wd3121 will automatically enter pulse skipping mode (psm) . when the converter output voltage is slightly higher than 5v , the device will stop switching and skip some periods to maintain output regulation. the wd3121 is highly integrated with a low on - resistance n - mos switch, internal control - loop compensation network and soft - start circuitry. addit ional features include cycle - by - cycle current limit protection, u nder voltage protection and over temperature protection . start - up the build - in soft - start function of wd3121 is implement ed to suppress the inrush current to an acceptable value at the begin ning of power on. cycle by cycle current limit the wd3121 uses a cycle - by - cycle current limit circuitry to limit the inductor peak current in the event of an overload condition. the current flow through inductor in charging phase is detected by a current sensing circuit. as the value comes across the current limiting threshold t he n - mosfet turns off , so that the inductor will be forced to leave charging stage and enter discharging stage. therefore, the inductor current will not increase over the current l imiting threshold . uvlo protection to avoid malfunction of the wd3121 at low input voltages, an under voltage lockout is included that disables the device, until the input voltage exceeds 2.2v ( typ. ). shutdown mode drive en to gnd to place the wd3121 in s hutdown mode. i n shutdown mode, the reference, control circuit , and the main switch turn off . i nput current falls to smaller than 1 a during shutdown mode. over temperature protection (otp) as soon as the junction temperature (t j ) exceeds 160 o c (typ.), the wd3121 goes into thermal shutdown. in this mode, the main n - mosfet is turned off until temperature falls below typically 130 o c. then the device starts switching again. note: * : wd3121e fixed 5v output voltage wd3121e 51 fixed 5.1v output volt age wd3121e 52 fixed 5.2v output voltage wd312 1 8 of 11 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
application i nformation e xternal component selection for the application circuit depends on the load current requirements . c ertain tradeoffs between different performance parameters can also be made. boost inductor selection a 2.2 u h inductor is recommended to connect from vdd to lx. t he minimum and maximum inductor values are constrained by many considerations . the minimum inductance is limited by the peak inductor - current value. the ripple current in the inductor is inversely proportional to the inductance value, so the output voltage may fall out o f r egulation if the peak inductor current exceeds the current - li mit value ( 2.75 a minimum). using a nominal 2.2 u h inductor allows full recommended current operation even if the inductance is 20% low (1.76 u h) due to component variation. a maximum 4.7 u h (typical) inductor value is recommended to maintain adequate phase margin over the full range of recommended operating conditions . t he saturation current of inductor should be higher enough than the peak switch current. and the inductor should have low core losses at 1mhz and low dcr (copper wire resistance). input capacitor selection connect the input capacitance from vdd to the reference ground plane. input capacitance red uces the ac voltage ripple on the input rail by providing a low - impedance path for the switching current of the boost converter. the wd3121 does not have a minimum or maximum input capacitance require - ment for operation, but a 22u f, x7r or x5r ceramic cap acitor is recommended for most applications for reasonable input - voltage ripple performance. there are several scenarios where it is reco mmended to use additional input capacitance . output capacitor selection connect the boost - converter output capacitance from output to the reference ground plane. the output capacitance controls the ripple voltage on the output rail and provides a low - impedance path for the switching and transient - load currents of the boost converter. it also sets the location of the output pole in the control loop of the boost converter. there are limitations to the minimum and maximum capacitance on output . the recommend ed minim um capacit ors on output are two 22 u f, x5r or x7r ceramic capacitor. the low esr of the ceramic capacitor minimize s ripple voltage and power dissipation from the large, pulsating currents of the boost converter and provides adequate phase margin a cross all recommended operating conditions. diode selection the rectifier diode supplies current path to the inductor when the internal mosfet is off. use a schottky with low forward voltage to reduce losses. the diode should be rated for a reverse blocking voltage greater than the output voltage used. the average current rating must be greater than the maximum load current ex pected, and the peak current rating must be greater than the peak inductor current. diode the following requirements: ? low forward voltage ? high switching speed : 50 ns max. ? reverse voltage : vout + vf or more ? rated current : ipk or more diode example: de vice package wsb5509l so d - 123fl wd312 1 9 of 11 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
pc b layout considerations a good circuit board layout aids in extracting the most performance from the wd3121 . p oor circuit layout degrades the output ripple and the electr omagnetic interference (emi) or electro - ma g netic compatibility (emc) performance. t he evaluation board layo ut is optimized for the wd3121 . u se this layout for best performance. i f this layout needs changing, use the following guidelines: 1. use separate analog and power ground planes. c onnect the sens itive analog circuitry (such as voltage divider components) to analog ground; connect the power components (such as input and output bypass capacitors) to power ground. c onnect the two ground planes together near the load to reduce the effects of voltage dropped on circuit board traces. locate c in as close to the v dd pin as possible, and use separate input bypass capacitors for the analog. 2. route the high current path from c in , through l to the lx and gnd pins as short as possible. 3. keep high current traces as short and as wide as possible. 4. the output filter of the boost converter is also critical for layout. the diode and output capacitors should be placed to minimize the ar ea of current loop through output C gnd C lx . 5. avoid routing high impedance traces, such as output , near the high current traces and components or near the diode node ( d ). 6. if high impedance traces are routed near high current and/or the lx node, place a ground plane shield between the traces. wd3121 demo board layout (top) wd3121 demo board layout (bottom) wd3121 demo board schematic vdd gnd lx en out l / 2 . 2 h wsb 5509 l cout 1 22 f cin 22 f v in en vout cout 2 22 f nc wd 3121 wd312 1 10 of 11 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification vdd gnd lx en out l / 2 . 2 h wsb 5509 l cout 1 22 f cin 22 f v in en vout cout 2 22 f nc wd 3121
package outline dimensions sot - 23 - 6 l symbol dimensions in millimeter min. typ. max. a 1.050 - 1.250 a1 0.000 - 0.100 a2 1.050 - 1.150 b 0.300 - 0.500 c 0.100 - 0.200 d 2.820 2.900 3.020 e 1.500 1.600 1.700 e1 2.650 2.800 2.950 e 0.950(bsc) e1 1.800 - 2.000 l 0.300 - 0.600 0 - 8 wd312 1 11 of 11 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification

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