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general description the HWD20011/hwd2001/hwd20012 compact, high efficiency, step-up dc-dc converters fit in small msop packages. they feature a built-in synchronous rectifier, which improves efficiency and reduces size and cost by eliminating the need for an external schottky diode. quiescent supply current is only 16?. the input voltage ranges from 0.7v to v out , where v out can be set from 2v to 5.5v. start-up is guaran- teed from 1.1v inputs. the HWD20011/hwd2001/ hwd20012 have a preset, pin-selectable output for 5v or 3.3v. the outputs can also be adjusted to other volt- ages using two external resistors. all three devices have a 0.3 ? n-channel mosfet power switch. the HWD20011 has a 1a current limit. the hwd2001 has a 0.5a current limit, which permits the use of a smaller inductor. the hwd20012 comes in a 10-pin msop package and features an adjustable cur- rent limit and circuitry to reduce inductor ringing. ________________________applications pagers wireless phones medical devices hand-held computers pdas rf tags 1 to 3-cell hand-held devices ____________________________features 94% efficient at 200ma output current 16a quiescent supply current internal synchronous rectifier (no external diode) 0.1a logic-controlled shutdown lbi/lbo low-battery detector selectable current limit for reduced ripple low-noise, anti-ringing feature (hwd20012) 8-pin and 10-pin msop packages preassembled evaluation kit (hwd20012evkit) HWD20011/hwd2001/hwd20012 high-efficiency, low-supply-current, compact, step-up dc-dc converters 1 gnd lbo shdn ref 1 2 8 7 out lx lbi fb HWD20011 hwd2001 msop top view 3 4 6 5 1 2 3 4 5 10 9 8 7 6 out lx gnd batt clsel lbo lbi fb hwd20012 msop shdn ref HWD20011 hwd2001 input 0.7v to v out shdn lx lbo out lbi 0.1 f low-battery detect out off on ref gnd fb output 3.3v, 5v, or adj (2v to 5.5v) up to 300ma low-battery detect in part HWD20011eua -40? to +85? temp. range pin-package 8 msop _______________ordering information hwd2001eua -40? to +85? 8 msop hwd20012eub -40? to +85? 10 msop typical operating circuit pin configurations
HWD20011/hwd2001/hwd20012 high-efficiency, low-supply-current, compact, step-up dc-dc converters 2 absolute maximum ratings electrical characteristics (v batt = 2v, fb = out (v out = 3.3v), r l = , t a = 0?c to +85?c , unless otherwise noted. typical values are at t a = +25?c.) supply voltage (out to gnd) ..............................-0.3v to +6.0v switch voltage (lx to gnd) .....................-0.3v to (v out + 0.3v) battery voltage (batt to gnd).............................-0.3v to +6.0v shdn lbo s s
HWD20011/hwd2001/hwd20012 high-efficiency, low-supply-current, compact, step-up dc-dc converters 3 electrical characteristics (v batt = 2v, fb = out, r l = , t a = -40?c to +85?c , unless otherwise noted.) (note 4) v out = 2v, i load = 1ma v out = 3.3v, i load = 200ma = gnd conditions % 85 efficiency 90 a 0.1 1 shutdown current into out units min typ max symbol parameter hwd20012, v batt = 2v v = 5.5v, v lbi = 5.5v v lbi = 0, i sink = 1ma v = 0 or v out v fb = 1v, v out = 3.3v hwd20012, clsel = out v lbi = 1.4v v fb = 1.4v v fb = 1v, v out = 3.3v 0.8v out v ih 0.2v out v il clsel input voltage v 0.8v out v ih 0.2v out v il input voltage 88 150 damping switch resistance a 0.07 1 i off leakage current v 0.2 0.4 low output voltage na 0.07 50 i input current a 1.4 3 i clsel clsel input current na 150 i lbi lbi input current na 0.03 50 i fb fb input current s 0.8 1 1.2 t off lx switch off-time s 347 t on lx switch on-time v electrical characteristics (continued) (v batt = 2v, fb = out (v out = 3.3v), r l = , t a = 0?c to +85?c , unless otherwise noted. typical values are at t a = +25?c.) fb = gnd fb = out v fb = 1v, v out = 3.3v v fb = 1v, v out = 3.3v = gnd v fb = 1.4v, v out = 3.3v i ref = 0 hwd2001, hwd20012 (clsel = gnd) hwd20012, hwd20012 (clsel = out) conditions 0.36 0.69 a 0.75 1.25 i lim lx switch current limit (nfet) v 2.20 5.5 output voltage range v 4.75 5.25 3.13 3.47 v out output voltage s 0.75 1.25 t off lx switch off-time s 2.7 7.0 t on lx switch on-time a 1 shutdown current into out a 40 operating current into out (note 3) v 1.2675 1.3325 v ref reference voltage v 1.2675 1.3325 fb, lbi thresholds 0.6 r ds(on) internal nfet, pfet on-resistance units min max symbol parameter v fb = 1.4v, v out = 3.3v a 16 35 operating current into out (note 3)
HWD20011/hwd2001/hwd20012 high-efficiency, low-supply-current, compact, step-up dc-dc converters 4 typical operating characteristics (l = 22?, c in = 47?, c out = 47? 0.1?, c ref = 0.1?, t a = +25?, unless otherwise noted.) v = 5.5v, v lbi = 5.5v v shdn = 0 or v out hwd20012, clsel = out conditions ? 1 i off leakage current na 75 i input current ? 3 i clsel clsel input current units min max symbol parameter electrical characteristics (continued) (v batt = 2v, fb = out, r l = , t a = -40? to +85? , unless otherwise noted.) (note 4) note 1: start-up voltage operation is guaranteed with the addition of a schottky mbr0520 external diode between the input and output. note 2: steady-state output current indicates that the device maintains output voltage regulation under load. see figures 5 and 6. note 3: device is bootstrapped (power to the ic comes from out). this correlates directly with the actual battery supply. note 4: specifications to -40? are guaranteed by design, not production tested. 100 0 0.01 0.1 1 10 100 1000 efficiency vs. load current 20 30 10 HWD20011 toc01 load current (ma) efficiency (%) 40 50 60 70 90 80 v in = 1.2v v out = 5v i limit = 500ma v in = 2.4v v in = 3.6v 100 0 0.01 0.1 1 10 100 1000 efficiency vs. load current 20 30 10 HWD20011 toc02 load current (ma) efficiency (%) 40 50 60 70 90 80 v in = 1.2v v out = 5v i limit = 1a v in = 2.4v v in = 3.6v 100 0 0.01 0.1 1 10 100 1000 efficiency vs. load current 20 30 10 HWD20011 toc03 load current (ma) efficiency (%) 40 50 60 70 90 80 v in = 1.2v v out = 3.3v i limit = 500ma v in = 2.4v 100 0 0.01 0.1 1 10 100 1000 efficiency vs. load current 20 30 10 HWD20011 toc04 load current (ma) efficiency (%) 40 50 60 70 90 80 v in = 1.2v v out = 3.3v i limit = 1a v in = 2.4v 1.290 1.292 1.296 1.294 1.298 1.300 -40 0 -20 20 40 60 80 100 reference output voltage vs. temperature HWD20011 toc05 temperature (?c) reference output voltage (v) i ref = 0 i ref = 100 a
HWD20011/hwd2001/hwd20012 high-efficiency, low-supply-current, compact, step-up dc-dc converters 5 0 40 20 100 80 60 140 120 160 0 1.5 2.0 0.5 1.0 2.5 3.0 3.5 4.0 4.5 no-load battery current vs. input battery voltage HWD20011 toc07 input battery voltage (v) input battery current ( a) i limit = 1a, 5.0v i limit = 0.5a, 5.0v i limit = 0.5a, 3.3v i limit = 1a, 3.3v 1.8 0 0.01 1 10 0.1 100 start-up voltage vs. load current 0.2 0.4 HWD20011 toc08 load current (ma) start-up voltage (v) 0.8 0.6 1.0 1.2 1.4 1.6 without diode with 1n5817 -1.0 -0.6 -0.8 -0.2 -0.4 0.2 0 0.4 0.8 0.6 1.0 1 2.0 2.5 3.0 1.5 3.5 4.0 4.5 5.0 5.5 shutdown current vs. supply voltage HWD20011 toc09 supply voltage (v) shutdown current ( a) 0 0.4 0.2 0.8 0.6 1.2 1.0 1.4 0 1.0 1.5 0.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 shutdown threshold vs. supply voltage HWD20011 toc10 supply voltage (v) shutdown threshold (v) 0 200 100 500 300 400 800 700 600 900 1.0 2.0 1.5 2.5 3.0 3.5 4.0 4.5 maximum output current vs. input voltage (v out = 5v) HWD20011 toc11 input voltage (v) maximum output current (ma) 1a current limit 0.5a current limit 0 200 100 400 300 600 500 800 700 1.0 1.4 1.6 1.2 1.8 2.0 2.2 2.4 2.6 2.8 3.0 maximum output current vs. input voltage (v out = 3.3v) HWD20011 toc12 input voltage (v) maximum output current (ma) 0.5a current limit 1a current limit typical operating characteristics (continued) (l = 22h, c in = 47f, c out = 47f 0.1f, c ref = 0.1f, t a = +25?c, unless otherwise noted.) 1 s/div heavy-load switching waveforms HWD20011 toc13 v lx 5v/div i lx 0.5a/div v out ac coupled 100mv/div v in = 2.4v v out = 5.0v 0 0.4 0.2 0.8 0.6 1.0 1.2 2.0 3.0 3.5 2.5 4.0 4.5 5.0 lx current limit vs. output voltage HWD20011 toc14 output voltage (v) i lim (a) HWD20011, hwd20012 (clsel = out) hwd2001,hwd20012 (clsel = gnd) 0 0.15 0.10 0.05 0.25 0.20 0.35 0.30 0.45 0.40 -60 -20 -40 0 20 40 60 80 100 switch resistance vs. temperature HWD20011 toc13.5 temperature ( ? c) resistance ( ) p-channel n-channel
10 s/div line-transient response HWD20011 toc15 v in 2v to 3v 1v/div v out ac coupled 100mv/div i load 100ma 5 s/div load-transient response HWD20011 toc16 i out 200ma/div v out 50mv/div ac coupled v in = 2.4v v out = 3.3v 500 s/div exiting shutdown HWD20011 toc17 v shdn 2v/div v out 2v/div HWD20011/hwd2001/hwd20012 high-ef ficiency , low-supply-cur r ent, compact, step-up dc-dc converters 6 typical operating characteristics (continued) (l = 22h, c in = 47f, c out = 47f 0.1f, c ref = 0.1f, t a = +25?c, unless otherwise noted.) pin description pin name function HWD20011 hwd2001 hwd20012 1 1 fb dual-modea feedback input. connect to gnd for +5.0v output. connect to out for +3.3v output. use a resistor network to set the output voltage from +2.0v to +5.5v. 2 2 lbi low-battery comparator input. internally set to trip at +1.30v. 3 3 open-drain low-battery comparator output. connect to out through a 100k resistor. output is low when v lbi is <1.3v. is high impedance during shutdown. ? 4 clsel current-limit select input. clsel = out sets the current limit to 1a. clsel = gnd sets the current limit to 0.5a. 4 5 ref 1.3v reference voltage. bypass with a 0.1f capacitor. 5 6 shutdown input. drive high (>80% of v out ) for operating mode. drive low (<20% of v out ) for shutdown mode. connect to out for normal operation. ? 7 batt battery input and damping switch connection. if damping switch is unused, leave batt unconnected. 6 8 gnd ground 7 9 lx n-channel and p-channel power mosfet drain 8 10 out power output. out provides bootstrap power to the ic.
detailed description the HWD20011/hwd2001/hwd20012 compact, step-up dc-dc converters start up with voltages as low as 0.9v and operate with an input voltage down to 0.7v. consuming only 16? of quiescent current, these devices offer a built-in synchronous rectifier that reduces cost by eliminating the need for an external diode and improves overall efficiency by minimizing losses in the circuit (see synchronous rectification sec- tion for details). the internal mosfet resistance is typi- cally 0.3 , which minimizes losses. the current limit of the HWD20011 and hwd2001 are 1a and 0.5a, respec- tively. the hwd2001's lower current limit allows the use of a physically smaller inductor in space-sensitive applications. the hwd20012 features a circuit that elimi- nates noise due to inductor ringing. in addition, the hwd20012 offers a selectable current limit (0.5a or 1a) for design flexibility. pfm control scheme a unique minimum-off-time, current-limited, pulse-fre- quency-modulation (pfm) control scheme is a key fea- ture of the HWD20011/hwd2001/hwd20012. this scheme combines the high output power and efficiency of a pulse-width-modulation (pwm) device with the ultra-low quiescent current of a traditional pfm ( figure 1 ). there is no oscillator; a constant-peak-current limit in the switch allows the inductor current to vary between this peak limit and some lesser value. at light loads, the switching frequency is governed by a pair of one-shots that set a typical minimum off-time (1?) and a typical maximum on-time (4?). the switching frequency depends upon the load and the input voltage, and can range up to 500khz. the peak current of the internal n- channel mosfet power switch is fixed at 1a (HWD20011), at 0.5a (hwd2001), or is selectable (hwd20012). unlike conventional pulse-skipping dc-dc converters (where ripple amplitude varies with input voltage), ripple in these devices does not exceed the product of the switch current limit and the filter-capaci- tor equivalent series resistance (esr). synchronous rectification the internal synchronous rectifier eliminates the need for an external schottky diode, thus reducing cost and board space. during the cycle off-time, the p-channel mosfet turns on and shunts the mosfet body diode. HWD20011/hwd2001/hwd20012 high-efficiency, low-supply-current, compact, step-up dc-dc converters 7 HWD20011 hwd2001 hwd20012 one-shot trig q f/f r s q one-shot trig q current-limit amplifier error amplifier low-battery comparator reference ref fb v in 47 f 47 f r1 200 r5 r6 damping switch 22 h batt (hwd20012) gnd lx out 0.1 f 0.1 f v out r4 lbi lbo r2 100k r3 v in v out clsel (hwd20012) shdn minimum off-time one-shot zero crossing amplifier en maximum on-time one-shot p n figure 1. simplified functional diagram
HWD20011/hwd2001/hwd20012 as a result, the synchronous rectifier significantly improves efficiency without the addition of an external component. conversion efficiency can be as high as 94%, as shown in the typical operating characteristics . for low-voltage inputs from single cells (alkaline, nicd, or nimh), use an external schottky diode such as the 1n5817 to ensure start-up. voltage reference the voltage at ref is nominally +1.30v. ref can source up to 100? to external circuits. the reference maintains excellent load regulation (see typical oper- ating characteristics ). a bypass capacitor of 0.1? is required for proper operation. shutdown the device enters shutdown when v shdn is low (v shdn <20% of v out ). for normal operation, drive shdn high (v shdn >80% of v out ) or connect shdn to out. during shutdown, the body diode of the p- channel mosfet allows current flow from the battery to the output. v out falls to approximately v in - 0.6v and lx remains high impedance. the capacitance and load at out determine the rate at which v out decays. shutdown can be pulled as high as 6v, regardless of the voltage at out. current limit select pin (hwd20012) the hwd20012 allows a selectable inductor current limit of either 0.5a or 1a. this allows flexibility in designing for higher current applications or for smaller, compact designs. connect clsel to out for 1a or to gnd for 0.5a. clsel draws 1.4? when connected to out. batt/damping switch (hwd20012) the hwd20012 is designed with an internal damping switch to minimize ringing at lx. the damping switch connects an external resistor (r1) across the inductor when the inductor? energy is depleted (figure 2). normally, when the energy in the inductor is insufficient to supply current to the output, the capacitance and inductance at lx form a resonant circuit that causes ringing. the ringing continues until the energy is dissi- pated through the series resistance of the inductor. the damping switch supplies a path to quickly dissipate this energy, minimizing the ringing at lx. damping lx ring- ing does not reduce v out ripple, but does reduce emi. r1 = 200 works well for most applications while reduc- ing efficiency by only 1%. larger r1 values provide less damping, but have less impact on efficiency. generally, lower values of r1 are needed to fully damp lx when the v out /v in ratio is high (figures 2, 3, and 4). high-efficiency, low-supply-current, compact, step-up dc-dc converters 8 hwd20012 damping switch batt r1 200 lx out 22 h v in 0.1 f 47 f v out figure 2. simplified diagram of inductor damping switch 2 s/div v lx 1v/div figure 3. lx ringing without damping switch 2 s/div v lx 1v/div figure 4. lx waveform with damping switch (with 200 external resistor)
selecting the output voltage v out can be set to 3.3v or 5.0v by connecting the fb pin to gnd (5v) or out (3.3v) (figures 5 and 6). to adjust the output voltage, connect a resistor-divider from v out to fb to gnd (figure 7). choose a value less than 260k for r6. use the following equation to calculate r5: r5 = r6 [(v out / v ref ) - 1] where v ref = +1.3v and v out may range from 2v to 5v. the input bias current of fb has a maximum value of 50na which allows large-value resistors (r6 260k ) to be used. low-battery detection the HWD20011/hwd2001/hwd20012 contain an on-chip comparator for low-battery detection. if the voltage at lbi falls below the internal reference voltage (1.30v), (an open-drain output) sinks current to gnd. the low-battery monitor threshold is set by two resistors, r3 and r4 (figures 5, 6, and 7). since the lbi current is less than 50na, large resistor values (r4 260k ) can be used to minimize loading of the input supply. calculate r3 using the following equation: r3 = r4 [(v trip / v ref ) - 1] for v trip 1.3v. v trip is the level where the low-battery detector output goes low, and v ref is the internal 1.30v reference. connect a pull-up resistor of 100k or greater from to out when driving cmos circuits. is an open-drain output, and can be pulled as high as 6v regardless of the voltage at out. when lbi is above the threshold, the output is high imped- ance. if the low-battery comparator is not used, ground HWD20011/hwd2001/hwd20012 high-efficiency, low-supply-current, compact, step-up dc-dc converters 9 HWD20011 hwd2001 hwd20012 batt (hwd20012) v in lbi ref gnd r3 r1 200 r4 r2 100k 47 f 22 h 0.1 f lx lbo 0.1 f 47 f output +3.3v v out low-battery output fb shdn out clsel (hwd20012) figure 5. preset output voltage of +3.3v HWD20011 hwd2001 hwd20012 batt (hwd20012) v in lbi ref gnd r6 r5 r3 r1 200 r4 r2 100k 22 h 47 f 0.1 f lx lbo output 2v to 5.5v fb shdn out clsel (hwd20012) low- battery output 0.1 f 47 f figure 7. setting an adjustable output HWD20011 hwd2001 hwd20012 batt (hwd20012) v in lbi ref gnd r3 r1 200 r4 r2 100k 22 h 47 f 0.1 f lx lbo 0.1 f 47 f output 5.0v fb shdn out clsel (hwd20012) low- battery output figure 6. preset output voltage of +5v
HWD20011/hwd2001/hwd20012 lbi and . for v trip less than 1.3v, configure the comparator as shown in figure 8. calculate the value of the external resistors r3 and r4 as follows: r3 = r4(v ref - v trip ) / (v out - v ref ) since the low-battery comparator is noninverting, exter- nal hysteresis can be added by connecting a resistor between and lbi as shown in figure 9. when is high, the series combination of r2 and r7 source current into the lbi summing junction. applications information inductor selection an inductor value of 22h performs well in most appli- cations. the HWD20011/hwd2001/hwd20012 will also work with inductors in the 10h to 47h range. smaller inductance values typically offer a smaller physical size for a given series resistance, allowing the smallest overall circuit dimensions. however, due to higher peak inductor currents, the output voltage ripple (i peak x output filter capacitor esr) also tends to be higher. circuits using larger inductance values exhibit higher output current capability and larger physical dimen- sions for a given series resistance. the inductor?s incre- mental saturation current rating should be greater than the peak switch-current limit, which is 1a for the HWD20011, 500ma for the hwd2001, and 1a or 0.5a for the hwd20012. however, it is generally acceptable to bias the inductor into saturation by as much as 20%, although this will slightly reduce efficiency. table 1 lists suggested components. the inductor?s dc resistance significantly affects effi- ciency. see table 2 for a comparison of inductor speci- fications. calculate the maximum output current as follows: where i out(max) = maximum output current in amps v in = input voltage l = inductor value in h = efficiency (typically 0.9) t off = lx switch?s off-time in s i lim = 0.5a or 1.0a i v v it vv xl out max in out lim off out in
e e 2 high-efficiency, low-supply-current, compact, step-up dc-dc converters 10 HWD20011 hwd2001 hwd20012 batt (hwd20012) v in lbi ref gnd r3 r1 200 r4 22 h 47 f 0.1 f lx lbo v out fb r2 100k shdn out clsel (hwd20012) low- battery output 0.1 f 47 f figure 8. setting resistor values for the low-battery indicator when v in < 1.3v HWD20011 hwd2001 hwd20012 lbi gnd v trip (v h , v l ) r3 r4 r7 v h is the upper trip level v l is the lower trip level where r2 100k lbo out v out 0.1 f 47 f v = 1.3v v = 1.3v h l

( .) (. ) ( ) 1 3 7 3 4 1 3 4 13 3 13 2 7 r r r r r r vvr vr r out figure 9. adding external hysteresis to the low-battery indicator
capacitor selection a 47f, 10v surface-mount tantalum (smt) output filter capacitor provides 80mv output ripple when stepping up from 2v to 5v. smaller capacitors (down to 10f with higher esrs) are acceptable for light loads or in applications that can tolerate higher output ripple. values in the 10f to 100f range are recommended. the equivalent series resistance (esr) of both bypass and filter capacitors affects efficiency and output rip- ple. output voltage ripple is the product of the peak inductor current and the output capacitor esr. use low-esr capacitors for best performance, or connect two or more filter capacitors in parallel. low-esr, smt tantalum capacitors are currently available from sprague (595d series) avx (tps series) and other sources. ceramic surface-mount and sanyo os-con organic-semiconductor through-hole capacitors also exhibit very low esr, and are especially useful for oper- ation at cold temperatures. see table 3 for a list of sug- gested component suppliers. HWD20011/hwd2001/hwd20012 high-efficiency, low-supply-current, compact, step-up dc-dc converters 11 production method inductors capacitors rectifiers (optional) surface mount sumida cd43 series sumida cd54 series coilcraft dt1608c coilcraft do1608c coiltronics uni-pac murata lqh4 series sprague 593d series sprague 595d series avx tps series ceramic motorola mbr0530 nihon ec 15qs02l miniature through-hole sumida rch654-220 sanyo os-con series table 1. suggested components table 2. surface-mount inductor specifications manufacturer part number ? (max) i peak (a) height (mm) coilcraft dt1608c-103 10 0.095 0.7 2.92 coilcraft do1608c-153 15 0.200 0.9 2.92 coilcraft do1608c-223 22 0.320 0.7 2.92 coiltronics up1b-100 10 0.111 1.9 5.0 table 3. component suppliers company phone fax avx usa (803) 946-0690 usa (803) 626-3123 coilcraft usa (847) 639-6400 usa (847) 639-1469 coiltronics usa (561) 241-7876 usa (561) 241-9339 murata usa (814) 237-1431 (800) 831-9172 usa (814) 238-0490 nihon usa (805) 867-2555 japan 81-3-3494-7411 usa (805) 867-2556 japan 81-3-3494-7414 motorola usa (303) 675-2140 (800) 521-6274 usa (303) 675-2150 sanyo usa (619) 661-6835 japan 81-7-2070-6306 usa (619) 661-1055 japan 81-7-2070-1174 sumida usa (647) 956-0666 japan 81-3-3607-5111 usa (647) 956-0702 japan 81-3-3607-5144 taiyo yuden usa (408) 573-4150 usa (408) 573-4159 sprague usa (603) 224-1961 usa (603) 224-1430 coiltronics up1b-150 15 0.175 1.5 5.0 coiltronics up1b-220 22 0.254 1.2 5.0 murata lqh4n100 10 0.560 0.4 2.6 murata lqh4n220 22 0.560 0.4 2.6 sumida cd43-8r2 8.2 0.132 1.26 3.2 sumida cd43-100 10 0.182 1.15 3.2 sumida cd54-100 10 0.100 1.44 4.5 sumida cd54-180 18 0.150 1.23 4.5 sumida cd54-220 22 0.180 1.11 4.5
HWD20011/hwd2001/hwd20012 high-efficiency, low-supply-current, compact, step-up dc-dc converters 12 _ __ transistor count: 751 chip information package information optional external rectifier although not required, a schottky diode (such as the mbr0520) connected between lx and out allows lower start-up voltages (figure 10) and is recommend- ed when operating at input voltages below 1.3v. note that adding this diode provides no significant efficiency improvement. pc board layout and grounding careful printed circuit layout is important for minimizing ground bounce and noise. keep the ic?s gnd pin and the ground leads of the input and output filter capaci- tors less than 0.2in (5mm) apart. in addition, keep all connections to the fb and lx pins as short as possi- ble. in particular, when using external feedback resis- tors, locate them as close to the fb as possible. to maximize output power and efficiency and minimize output ripple voltage, use a ground plane and solder the ic?s gnd directly to the ground plane. HWD20011 hwd2001 hwd20012 batt (hwd20012) v in lbi ref gnd r3 r1 200 ? figure 10. adding a schottky diode for low input voltage operation 10lumax.eps
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