WD1014EA 1.5mhz, 800ma synchronous step-down regulator in sot general description the WD1014EA is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. the 2.7v to 5.5v input voltage range makes the WD1014EA ideally suited for single li-ion battery-powered applications. supply current with no load is 2 5 a, dropping to <1 a in shut- down. pwm (pulse width modulation) operation provides very low output ripple voltage for noise sensitive applications. 100% duty cycle capability provides low dropout operation, extending battery life in portable systems. the switching frequency is internally set at 1.5mhz, allowing the use of tiny surface mount inductors and capacitors. low output voltages are easily supported with the 0.6v feedback reference voltage. the WD1014EA is available in sot - 23 package. the internal synchronous switch increas es efficiency and eliminates the need for an external schottky diode. ordering information top view order part number WD1014EA-5/tr part marking features 8 00ma output current high efficiency: up to 95% t iny 5-pin sot-23 package 1.5mhz constant frequency operation 2.7v to 5.5v input voltage range low dropout operation: 100% duty cycle low quiescent current: only 2 5 a during operation shutdown mode draws < 1 a supply current no schottky diode required 0.6v reference allows low output voltages over temperature protected adjustable output voltage. current mode operation for excellent line and load transient response applications cellular telephones personal information appliances wireless and dsl modems digital still cameras mp3 players portable instruments marking information typical application circuit figure 1. high efficient step-down converter w d14 330k 330k 1.2v device package shipping for marking information, contact our sales representative directly or through a willsemi distributor located in your area, otherwise visit our website for detail. WD1014EA-5/tr sot-23-5l 3000/tape&reel yyww 1 of 9 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
absolute maximum ratings (note 1) z input supply voltage .......................................................................................................... ............................................. C 0.3v to 6v z en, fb voltages ............................................................................................................... .............................................. C 0.3v to v in z sw voltage (dc) ............................................................................................................... ............................... C 0.3v to (v in + 0.3v) z p-channel switch source current (dc) .......................................................................................... .......................................... 15 00ma z n-channel switch sink current (dc) ............................................................................................ ........................................... 15 00ma z peak sw sink and source current ............................................................................................... .................................................. 1. 5 a z operating temperature range (note 2) .......................................................................................... ........................... C40 e c to 85 e c z maximum junction temperature (notes 4) ........................................................................................ ................................... 125 e c z storage temperature range ..................................................................................................... ............................... C 65 e c to 150 e c z lead temperature (soldering, 10 sec)........................................................................................... ............................................. 26 0 e c electrical characteristics (v in = 3.6v, v en = v in , t a = 0 to 85 . typical parameters are at t a = +25 , unless otherwise noted.) parameter symbol conditions min typ max units input voltage range v in 2.7 5.5 v under voltage lockout threshold v uvlo v in rising, hysteresis = 0.1v 2.25 2.40 2.60 v operating supply current i q (note 3)v fb = 60%, i out = 0a 150 250 a standby supply current i q (note 3)v fb = 105%, i out = 0a 2 5 30 a shutdown supply current i q v fb = 0v, i out = 0a 0.1 1 a adjustable version regulation voltage v fb t a = 25 0 ? t a ? 85 -40 ? t a ? 85 0.584 0.6 0.616 0.582 0.6 0.618 0.580 0.6 0.620 v v v output voltage line regulation v ? out v in = 3v to 5v 0.016 0.4 %/v output voltage load regulation v loadreg i out = 10ma to 500ma 0.5 % inductor limit current i lim v in = 3.6v, v out = 90% of v out(nom) 1. 0 1. 5 a oscillator frequency f osc v fb or v out in regulation v fb or v out to gnd 1.2 1.5 1.8 230 280 330 mhz khz r ds(on) of p-channel fet r pfet i sw = 100ma 0.37 0.6
r ds(on) of n-channel fet r nfet i sw = 100ma 0.36 0.6
feedback leakage current i fb 30 na sw leakage current i lsw v in = 5.5v, v sw = 0v or 5.5v 0.01 0.1 a en threshold voltage v en v in = 2.7 to 5.5v 0.4 1 1.4 v en leakage current i en v in = 5.5v, v en = 0v or v in 0.01 0.1 a WD1014EA 2 of 9 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
note1. absolute maxim um ratings are those values beyond which the life of a device may be impaired. note2. the wd101 4 ea is guaranteed to meet performance specifications from 0 to 70 . specifications over the C40 to 85 operating temperature range are assured by design, characterization and correlation with statistical process controls. note3. dynamic supply current is higher due to the gate charge being delivered at the switching frequency. note4. this ic includes over temperature protection that is intended to protect the device during momentary overload conditions. junction temperature will exceed 125 when over temperature protection is active. continuous operation above the specified maximum operating junction temperature may impair device reliability. pin functions typical performance characteristics v in (pin 1): main supply pin. must be closely deco- upled to gnd, pin 2, with a 2.2 f or greater ceramic capacitor. gnd (pin 2): ground pin. enable pin of the device. pulling this pin to ground forces the device into shutdown mode. pulling this pin to v in enables the device. this pin must not be left floating and must be terminated. feedback pin of the device. receives the feedback voltage from an external resistive divider across the output. connect the inductor to this pin. this pin is the switch pin and connected to the internal mosfet switches. en (pin 3): sw (pin 5): fb (pin 4): 0.1 1 10 100 1000 60 70 80 90 100 efficiency(%) efficiency vs output current output current(ma) v in =2.7v v in =3.6v v in =4.2v v out =1.8v 0.1 1 10 100 1000 45 50 55 60 65 70 75 80 85 90 95 v out =1.2v efficiency(%) efficiency vs output current output current(ma) v in =4.2v v in =3.6v v in =2.7v WD1014EA 3 of 9 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
3456 50 60 70 80 90 100 v out =1.8v i out =1ma i out =0.1ma i out =10ma i out =100ma i out = 8 00ma efficiency(%) efficiency vs input voltage input voltage(v) 3456 1.3 1.4 1.5 1.6 1.7 frequency vs input voltage i out = 8 00ma, v out =1.8v input voltage(v) frequency(mhz) 3456 0 50 100 150 200 v fb =0.7v v fb =0.5v i out =0ma,v out =1.8v supply current vs input voltage input voltage(v) supply current(ua) start-up from shutdown psm mode operation load step WD1014EA 4 of 9 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
function diagram theory of operation pwm control mode the wd101 4 ea step-down converter operates with typically 1.5mhz fixed-frequency pulse width modulation (pwm) at moderate to heavy load currents. both the main (p-channel mosfet) and synchronous (n-channel mosfet) switches are internal. during pwm operation, the converter uses a current-mode control scheme to achieve good line and load regulation. at the beginning of each clock cycle initiated by the clock signal, the main switch is turned on. the current flows from the input capacitor via the main switch through the inductor to the output capacitor and load. during this phase, the current ramps up until the pwm comparator trips and the control logic turns off the switch. after a dead time, which prevents shoot-through current, the synchronous switch is turned on and the inductor current ramps down. the current flows from the inductor to the output capacitor and to the load. it returns back to the inductor through the synchronous switch. the next cycle is initiated by the clock signal again turning off the synchronous switch and turning on the main switch. pulse skipping mode (psm) at light loads, the inductor current may reach zero or reverse on each pulse. the synchronous switch is turned off by the current reversal comparator, i rcmp , and the switch voltage will ring. this is discontinuous mode operation, and is normal behavior for the switching regulator. at very light loads, the wd101 4 ea will automatically skip pulses in pulse skipping mode (psm) operation to maintain output regulation. short-circuit protection when the output is shorted to ground, the frequency of the oscillator is reduced to about 280khz. this frequency foldback ensures that the inductor current has more time to decay, thereby preventing runaway. the oscillators frequency will progressively increase to 1.5mhz when v fb rises above 0v. WD1014EA 5 of 9 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
dropout operation the device starts to enter 100% duty-cycle mode once the input voltage comes close to the nominal output voltage. in order to maintain the output voltage, the main switch is turned on 100% for one or more cycles. the output voltage will then be determined by the input voltage minus the voltage drop across the p-channel mosfet and the inductor. shutdown mode drive en to gnd to place the wd101 4 ea in shut- down mode. in shutdown mode, the reference, control circuity, main switch, and synchronous switch turn off and the output becomes high impedance. input current falls to 0.1 a (typ) during shutdown mode. drive en high to enable the ic. under voltage lockout (uvlo) the wd101 4 ea do not operate with battery voltages below the uvlo threshold of 2.4v (typ). the output remains off until the supply voltage exceeds the uvlo threshold. the uvlo hysteresis is 0.1v (typ). this guarantees the integrity of the output voltage regulation. applications information external component selection for the application circuit depends on the load current requirements. certain tradeoffs between different performance parameters can also be made. inductor selection the wd101 4 ea high switching frequency allows the use of a physically small inductor. the inductor ripple current is determined by 1 ()() out out l in vv i fl v ' ? ? 1 where ? i l is the peak-to-peak inductor ripple current and f is the switching frequency. the inductor peak-to- peak current ripple is typically set to be 40% of the maximum dc load current. using this guideline and solving for l, () 1 (40% ) out out load max in vv l fi v ? ? 1 it is important to ensure that the inductor is capable of handling the maximum peak inductor current, i lpk , determined by () 2 l lpk load max i ii ' inductor core selection different core materials and shapes will change the size/current and price/current relationship of an inductor. toroid or shielded pot cores in ferrite or permalloy materials are small and dont radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. the choice of which style inductor to use often depends more on the price vs size requirements and any radiated field/emi requirements than on what the wd101 4 ea requires to operate. input capacitor selection capacitor esr is a major contributor to input ripple in high-frequency dc-dc converters. ordinary aluminum electrolytic capacitors have high esr and should be avoided. low-esr tantalum or polymer capacitors are better and provide a compact solution for space constrained surface-mount designs. ceramic capacitors have the lowest overall esr. the input filter capacitor reduces peak currents and noise at the input voltage source. connect a low-esr bulk capacitor (2.2 f to 10 f) to the input. select this bulk capacitor to meet the input ripple requirements and WD1014EA 6 of 9 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
voltage rating rather than capacitance value. use the following equation to calculate the maximum rms input current: out rms out in out in i ivvv v u output capacitor selection ceramic capacitors with low-esr values have the lowest output voltage ripple and are recommended. at nominal load current, the device operates in pwm mode, and the rms ripple current is calculated as: 1 1 23 out in rmscout out v v iv lf u u u u at nominal load current, the device operates in pwm mode, and the overall output voltage ripple is the sum of the voltage spike caused by the output capacitor esr plus the voltage ripple caused by charging and discharging the output capacitor: 1 1 8 out in out out v v vv esr lf c f ' u u ? u u u ? 1 at light load currents, the converter operates in pulse skipping mode, and the output voltage ripple is dependent on the capacitor and inductor values. larger output capacitor and inductor values minimize the voltage ripple in psm operation and tighten dc output accuracy in psm operation. output voltage setting the output voltage can be calculated as: 2 0.6 1 1 out r v r ? ? 1 the external resistive divider is connected to the output, allowing remote voltage sensing as shown in figure 2. to minimize the current through the feedback divider network, r1 should be larger than 100k
. the sum of r1 and r2 should not exceed 1 m
, to keep the network robust against noise. an external feed forward capacitor c fwd , is required for optimum load transient response. the value of c fwd should be in the range between 22pf and 33pf. route the fb line away from noise sources, such as the inductor or the sw line. figure 2. setting the WD1014EA output voltage pc board layout considerations a good circuit board layout aids in extracting the most performance from the wd101 4 ea. poor circuit layout degrades the output ripple and the electromagnetic interference (emi) or electromagnetic compatibility (emc) performance. the evaluation board layout is optimized for the wd101 4 ea. use this layout for best performance. if this layout needs changing, use the following guidelines: 1. use separate analog and power ground planes. connect the sensitive analog circuitry (such as voltage divider components) to analog ground; connect the power components (such as input and output bypass capacitors) to power ground. connect the two ground planes together near the load to reduce the effects of voltage dropped on circuit board traces. 2. locate c in as close to the v in pin as possible, and use separate input bypass capacitors for the analog and power grounds indicated in guideline 1. WD1014EA 7 of 9 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
3. route the high current path from c in , through l, to the sw and pgnd pins as short as possible. 4. keep high current traces as short and as wide as possible. 5. place the feedback resistors as close as possible to the fb pin to prevent noise pickup. 6. avoid routing high impedance traces, such as fb, near the high current traces and components or near the switch node (sw). 7. if high impedance traces are routed near high current and/or the sw node, place a ground plane shield between the traces. figure 3. WD1014EA layout diagram figure 4. WD1014EA suggested layout 4.7uf 10uf vin sw gnd en fb 2.2uh 2.7v to 5.5v v in v out c in l 5 3 4 1 2 c out r1 r2 c1 i r1 WD1014EA ? ? ? ? ? ? + = r1 r2 1 x v v ref out , =0.6v. v ref v out (v) r1(k
) r2(k
) 22p f the choose of external resistive divider WD1014EA 8 of 9 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
applications information sot23-5l package outline dimensions symbol dimensions in millimeters dimensions in inches 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 2.65 2.950 0.104 0.116 e 0.950(bsc) 0.037(bsc) e1 1.800 2.000 0.071 0.079 l 0.300 0.600 0.012 0.024 e 8 e e 8 e WD1014EA 9 of 9 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification
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