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| april 23, 2009 power management 2.5mhz, 1a synchronous step down regulator in sot23-5 SC4626 www.semtech.com typical application circuit features v in range: 2.9 C 5.5v v out options: .0 - 3.3v up to a output current 2.5mhz switching frequency efciency up to 93% low output noise across load range excellent transient response start up into pre-bias output 00% duty-cycle low dropout operation < a shutdown current internal soft start input under-voltage lockout output over-voltage, current limit protection over-temperature protection adjustable output voltage sot23-5 package -40 to 85c temperature range fully weee and rohs compliant applications bluetooth radios dsc and pmps gps devices xdsl systems pol regulators portable hdd wireless lan ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? description the SC4626 is a high efciency, synchronous step-down regulator providing up to a output current in a sot23- 5 package. the device requires only three external flter components for a complete step-down regulator solution. the input voltage range is 2.9 to 5.5v with either factory programmed outputs from .0 to 3.3v or adjustable output via an external resistor divider. the converter operates at fxed 2.5mhz switching frequency allowing small l/c fltering components. the voltage mode architecture is compatible with chip inductors and capacitors for minimum pcb footprint and lowest overall system cost. up to 93% efciency is achieved with l ow r ds(on) internal switches. pwm constant frequency operation ensures low output ripple across the load range. 00% duty-cycle provides 300mv dropout voltage at a which extends the minimum input voltage for 2.5v and 3.3v outputs. excellent transient response is achieved with no external compensation components. the SC4626 provides input under-voltage, output over- voltage, output short circuit and over-temperature protection to safeguard the device and system under fault conditions. the regulator provides integrated soft-start to minimize inrush currents. standby quiescient current is less than a. the SC4626 is available in a sot23-5 package rated for -40 to +85c ambient temperature range. en gnd c in 10f v in 2.9v to 5.5v v out 1.20v/1a c out 10f l 2.2h lx vout enable SC4626c vin
www.semtech.com ? 2009 semtech corp. 2 SC4626 pin confguration ordering information device package & description SC4626xsktrt (2)(3)(4) sot23-5 SC4626xevb (5) evaluation board - standard size (i.e., wire wound inductor) SC4626xevb-1 (5) evaluation board - small size (i.e., chip inductor) notes: () measured in free convection, mounted on 0mm x 0mm, 2 layer fr4 pcb shown in fgure 4 with copper of oz for each layer. (2) available in tape and reel only. a reel contains 3,000 devices. (3) available in lead-free package only. device is weee and rohs compliant. (4) x is the code of the output voltage. see table for the code. for example, the device number for vout= .20v is SC4626csktrt. (5) x is the code of the output voltage. see table for the code. for example, the evb for vout= .20v is SC4626cevb (standard size) or SC4626cevb- (small size). table 1: available output voltages code vout () a .00 c .20 e .28 f .30 h .50 l .80 y 2.50 z 3.30 notes: () contact factory for unavaliable output voltage options. sot23-5 ja f=f90c/w (1) 1 2 3 5 4 vin gnd en lx vout (topfview) x marking for sot23, 5 lead package: x = code of the output voltage (example: c for vout= .20v) yyww = datecode (example: 0852) marking information www.semtech.com ? 2009 semtech corp. 3 SC4626 exceeding the absolute maximum ratings may result in permanent damage to the device and/or device malfunction. operation outside of the parameters specifed in the electrical characteristics section is not recommended. notes: () measured in free convection, mounted on 0mm x 0mm, 2 layer fr4 pcb shown in fgure 4 with copper of oz for each layer. (2) tested according to jedec standard jesd22-a 4-b. electrical characteristics recommended operating conditions vin supply voltage 2.9 to 5.5v maximum output current .0a temperature range -40 to +85 ? c thermal resistance, junction to ambient () 90c/w maximum junction temperature + 50c storage temperature range -65 to + 50 c thermal information absolute maximum ratings vin supply voltage -0.3 to 6.0v lx voltage .. - to v in + v, -3v (20ns max), 6v max vout voltage -0.3 to v in +0.3v en voltage . -0.3 to v in +0.3v peak ir reflow temperature . 260c esd protection level (2) . 3kv unless specifed: v in = 5.0v; -40c www.semtech.com ? 2009 semtech corp. 6 SC4626 typical characteristics ( continued ) linefregulation rdson (p& n) over line 110 130 150 170 190 210 2.5 3.0 3.5 4.0 4.5 5.0 5.5 input voltage (v) r ds(on) (m ? ) t a = 25c i lx = 100ma n-channel p-channel switching frequency variation over line -5% -4% -3% -2% -1% 0% 1% 2% 3% 4% 5% 2.5 3.0 3.5 4.0 4.5 5.0 5.5 input voltage (v) variation i out = 0a t a = 25c v out = 3.3v v out = 1.5v line regulation ove line -1.0% -0.8% -0.6% -0.4% -0.2% 0.0% 0.2% 0.4% 0.6% 0.8% 1.0% 2.5 3.0 3.5 4.0 4.5 5.0 5.5 input voltage (v) regulation i out = 0a t a = 25c v out = 3.3v v out = 1.5v rdson (p & n) over temperature 90 110 130 150 170 190 -40 -15 10 35 60 85 ambient temperature (c) r ds(on) (m ? ) v in = 5.0v i lx = 100ma n-channel p-channel switching frequency variation -1.0% -0.8% -0.6% -0.4% -0.2% 0.0% 0.2% 0.4% 0.6% 0.8% 1.0% -40 -15 10 35 60 85 ambient temperature (c) variation v in = 5.0v i out = 0a line regulation over temperature -1.0% -0.8% -0.6% -0.4% -0.2% 0.0% 0.2% 0.4% 0.6% 0.8% 1.0% -40 -15 10 35 60 85 ambient temperature (c) regulation v out = 1.5v i out = 0a linefregulationfvs.ftemperature r ds(on) fvs.finputfvoltage r ds(on) fvs.ftemperature switchingffrequencyfvs.finputfvoltage switchingffrequencyfvs.ftemperature circuit conditions: v out = .0v (SC4626a), .5v (SC4626h) & 3.3v (SC4626z);c in = 0uf/6.3v;c out = 0uf/6.3v for l=2.2uh;c out = 22uf/6.3v for l= uh. unless otherwise noted, l= 2.2uh (toko: 07 as-2r2m). www.semtech.com ? 2009 semtech corp. 7 SC4626 typical characteristics ( continued ) uvlofrisingfthresholdfvariation uvlo rising threshold variation -1.0% -0.8% -0.6% -0.4% -0.2% 0.0% 0.2% 0.4% 0.6% 0.8% 1.0% -40 -15 10 35 60 85 ambient temperature (c) variation i out = 0a uvlo hysteresis variation -5% -4% -3% -2% -1% 0% 1% 2% 3% 4% 5% -40 -15 10 35 60 85 ambient temperature (c) variation i out = 0a uvlofhysteresisfvariation dropoutfvoltagefinf100%fdutyfcyclefoperation loadfregulationf (v out =1.5v) loadfregulationf (v out =3.3v) circuit conditions: v out = .0v (SC4626a), .5v (SC4626h) & 3.3v (SC4626z);c in = 0uf/6.3v;c out = 0uf/6.3v for l=2.2uh;c out = 22uf/6.3v for l= uh. unless otherwise noted, l= 2.2uh (toko: 07 as-2r2m). load regulation -1.0% -0.8% -0.6% -0.4% -0.2% 0.0% 0.2% 0.4% 0.6% 0.8% 1.0% 0.0 0.2 0.4 0.6 0.8 1.0 output current (a) load regulation v in = 5.0v v in = 3.3v v out = 1.50v t a =25c load regulation -1.0% -0.8% -0.6% -0.4% -0.2% 0.0% 0.2% 0.4% 0.6% 0.8% 1.0% 0.0 0.2 0.4 0.6 0.8 1.0 output current (a) load regulation v in = 5.0v v in = 4.0v v out = 3.30v t a =25c dropout voltage of 100% duty cycle operation 0 50 100 150 200 250 300 350 400 0.0 0.2 0.4 0.6 0.8 1.0 output current (a) dropout voltage (mv) t a = 25c l= mdt2520-cr1r0m (dcr= 60m ? _typ) l= 1071as-2r2n (dcr=50m ? _typ) www.semtech.com ? 2009 semtech corp. 8 SC4626 outputfvoltagefripplef(v out =1.5v) outputfvoltagefripple f(v out =1.5v) transientfresponsef( v out =1.5v;f 0aftof0.5a) outputfvoltagefripple f(v out =1.5v) outputfvoltagefripple f(v out =1.5v) transientfresponsef( v out =1.5v;f 0.5aftof1.0a) v out 10mv/div v lx 2v/div i lx 500ma/div 500ns/div v in =5.0v i out =0a output voltage ripple (v out =1.5v) 4626 - w1 v out 10mv/div v lx 2v/div i lx 500ma/div 500ns/div v in =3.3v i out =0a output voltage ripple (v out =1.5v) 4626 - w3 v out 100mv/div i out 500ma/div 50s/div transient response (v out =1.5v) v in =5.0v i out =0a to 0.5a 4626 - w5 v out 10mv/div v lx 2v/div i lx 500ma/div 500ns/div output voltage ripple (v out =1.5v) v in =5.0v i out =1.0a 4626 - w2 v out 10mv/div v lx 2v/div i lx 500ma/div 500ns/div output voltage ripple (v out =1.5v) v in =3.3v i out =1.0a 4626 - w4 v out 100mv/div i out 500ma/div 50s/div transient response (v out =1.5v) v in =5.0v i out =0.5a to 1a 4626 - w6 typical waveforms circuit conditions: v out = .5v (SC4626h); l= 2.2uh (toko: 07 as-2r2m); c in = c out = 0uf/6.3v (murata: grm2br60j 06k). www.semtech.com ? 2009 semtech corp. 9 SC4626 startfupf(enable)( v out =1.5v) startfupf(powerfupfv in )f ( v out =1.5v) startfupfintofpre-biasfoutputf(enable) startfupf(enable)( v out =1.5v) startfupf(powerfupfv in )f ( v out =1.5v) shutdownf(disable)f ( v out =1.5v) v out 1v/div 100s/div start up (v out =1.5v) v in =5.0v r out =1k ? v en 2v/div v in 2v/div v out 500mv/div 200s/div start up (v out =1.5v), en=vin v in 2v/div v in =5.0v r out =1k ? v out 500mv/div 200s/div v in 2v/div v in =5.0v r out =1k ? start up into pre-biased output (v out =1.5v) enable v en 2v/div v out 1v/div 100s/div start up (v out =1.5v) v en 2v/div v in 2v/div v in =5.0v r out =1.5 ? v out 500mv/div 200s/div start up (v out =1.5v), en=vin v in 2v/div v in =5.0v r out =1.5 ? 50s/div shutdown-disable v out 500mv/div v en 2v/div v in 2v/div v in =5.0v r out =1.5 ? typical waveforms ( continued ) circuit conditions: v out = .5v (SC4626h); l= 2.2uh (toko: 07 as-2r2m); c in = c out = 0uf/6.3v (murata: grm2br60j 06k). www.semtech.com ? 2009 semtech corp. 0 SC4626 outputfvoltagefripplef(v out =3.3v) transientfresponsef( v out =3.3v;f 0aftof0.5a) startfupf(enable)( v out =3.3v) outputfvoltagefripple f(v out =3.3v) transientfresponsef( v out =3.3v;f 0.5aftof1.0a) startfupf(enable)( v out =3.3v) v out 10mv/div v lx 2v/div i lx 500ma/div 500ns/div output voltage ripple (v out =3.3v) v in =5.0v i out =0a 4626 - w13 v out 100mv/div i out 500ma/div 50s/div transient response (v out =3.3v) v in =5.0v i out =0a to 0.5a 4626 - w15 v out 1v/div 200s/div start up (v out =3.3v) v in =5.0v r out =1k ? v en 2v/div v in 5v/div v out 10mv/div v lx 2v/div i lx 500ma/div 500ns/div output voltage ripple (v out =3.3v) v in =5.0v i out =1.0a 4626 - w14 v out 100mv/div i out 500ma/div 50s/div transient response (v out =3.3v) v in =5.0v i out =0.5a to 1a 4626 - w16 v out 1v/div 200s/div start up (v out =3.3v) v en 2v/div v in 5v/div v in =5.0v r out =3.3 ? typical waveforms ( continued) circuit conditions: v out =3.3v (SC4626z); l= 2.2uh (toko: 07 as-2r2m); c in = c out = 0uf/6.3v (murata: grm2br60j 06k). www.semtech.com ? 2009 semtech corp. SC4626 startfupf(powerfupfv in )f ( v out =3.3v) startfupfintofpre-biasfoutputf(enable) shutdownf(disable)f ( v out =3.3v) startfupf(powerfupfv in )f ( v out =3.3v) startfupfintofpre-biasfoutputf(powerfupfv in ) shutdownf(disable)f ( v out =3.3v) v out 1v/div 200s/div start up (v out =3.3v), en=vin v in 2v/div v in =5.0v r out =1k ? v out 1v/div 200s/div start up into pre-biased output (v out =3.3v)(enable) v in =5.0v r out =1k ? v en 2v/div v in 2v/div 500s/div shutdown-disable (v out =3.3v) v out 2v/div v en 2v/div v in 5v/div v in =5.0v r out =33 ? v out 1v/div 200s/div start up (v out =3.3v), en=vin v in 2v/div v in =5.0v r out =3.3 ? v out 1v/div 200s/div start up into pre-biased output (v out =3.3v)(power up) v in =5.0v r out =1k ? v in 2v/div 100s/div shutdown-disable (v out =3.3v) v out 2v/div v en 2v/div v in 5v/div v in =5.0v r out =3.3 ? typical waveforms ( continued ) circuit conditions: v out =3.3v (SC4626z); l= 2.2uh (toko: 07 as-2r2m); c in = c out = 0uf/6.3v (murata: grm2br60j 06k). www.semtech.com ? 2009 semtech corp. 2 SC4626 outputfvoltagefripplef(v out =1.0v) outputfvoltagefripplef( v out =1.0v ) transientfresponsef( v out =1.0v ) outputfvoltagefripple f(v out =1.0v) outputfvoltagefripplef( v out =1.0v ) transientfresponsef( v out =1.0v ) v out 10mv/div v lx 2v/div i lx 500ma/div offset: 0a 500ns/div v in =3.3v i out =0a output voltage ripple (v out =1.0v) 4626 - w25 v out 10mv/div v lx 2v/div i lx 500ma/div 500ns/div v in =5.0v i out =0a output voltage ripple (v out =1.0v) 4626 - w27 v out 20mv/div i out 500ma/div 50s/div transient response (v out =1.0v) v in =5.0v i out =0a to 0.5a 4626 - w29 v out 10mv/div v lx 2v/div i lx 500ma/div 500ns/div output voltage ripple (v out =1.0v) v in =3.3v i out =1.0a 4626 - w26 v out 10mv/div v lx 2v/div i lx 1a/div 500ns/div output voltage ripple (v out =1.0v) v in =5.0v i out =1.0a 4626 - w28 v out 20mv/div i out 500ma/div 50s/div transient response (v out =1.0v) v in =5.0v i out =0.5a to 1a 4626 - w30 typical waveforms ( continued) circuit conditions: v out = .0v (SC4626a); l= .0uh (murata: lqm2hpnr0ng0l); c in = 0uf/6.3v; c out = 22uf/6.3v (murata: grm2 br60j226m). www.semtech.com ? 2009 semtech corp. 3 SC4626 pin descriptions pin # pin name pin function vin input power supplies. powers the internal circuitry and is connected to the source of high-side p channel mosfet. 2 gnd ground connection. 3 en enable pin. when connected to logic high or tied to vin pin, the SC4626 is on. when connected to logic low, the device enters shutdown and consumes less than a of current. the enable pin has a m internal pulldown resistor. this resistor is switched in circuit whenever the en pin is below the enable input high threshold, or when the part is in undervoltage lockout. 4 vout output voltage sense pin. 5 lx switching node - connect an inductor between this pin and the output capacitor. www.semtech.com ? 2009 semtech corp. 4 SC4626 block diagram control logic plimit amp current amp pwm comp error amp 500 mv ref vout gnd l x v in ramp generator internal oscillator + - + - + - v ovp ovp + - + - en voltage select plimit comp www.semtech.com ? 2009 semtech corp. 5 SC4626 detailed description the SC4626 is a synchronous step-down pulse width modulated (pwm) voltage mode dc-dc regulator operating at 2.5mhz fxed-frequency. the switching frequency is chosen to minimize the size of the external inductor and capacitors while maintaining high efciency. operation during normal operation, the internal high- side pmos device is activated on each ris - ing edge of the internal oscillator. the voltage feedback loop uses an internal feedback resistor divider. the period is set by the on board oscillator when in pwm mode at average to high loads. the device has an internal low-side synchronous nmos device and does not require a schottky diode on the lx pin. the device operates as a buck converter in pwm mode with a fxed frequency of 2.5mhz. output voltage selection the SC4626 is designed for fxed output voltage. there are some options for preset output voltage shown in table . if the voltage desired is not shown in the table , it can be programmed via an external resistor di - vider. there will be typical ua current fowing into the vout pin. the typical schematic of adjustable output voltage option from the part with standard .0v, the SC4626a, is shown in figure . the c ff is needed for maintain the performance of the transient response. the proper value of c ff can be calculated by the equation ( ) ( ) ) 5.0 ( ] [ 5.0 10 ] [ 1 2 ? ? ? ? ? = ostd ostd ostd out fb out ff v v v v k r v nf c ,where the v ostd is the standard voltage shown in table . to simplify the design, it is recommended to program the desired output voltage from standard .0v as shown in figure with a proper c ff calculated from the equation shown above. for programming the output voltage from other standard voltage, the r fb , r fb2 and c ff need to be adjusted to meet the equation shown above. protection features the SC4626 provides the following protection features: thermal shutdown current limit over-voltage protection soft-start operation thermal shutdown the device has a thermal shutdown feature to protect the SC4626 if the junction temperature exceeds 60c. during thermal shutdown, the on-chip power devices are disabled with the lx output foating. when the die temperature drops by 0c, the part will initiate a soft start recovery to normal operation. current limit the internal pmos power device in the switching stage is protected by current limit feature. if the output is loaded above the pmos current limit for 32 consecutive cycles, the SC4626 enters foldback current limit mode and the output current is limited to the current limit holding current (i cl_hold ) of a few hundred milliampere. under these conditions the output voltage will be the product of i cl_hold and the load resistance. the current limit holding current (i cl_hold ) will be decreased when output voltage is increased. the load presented must fall below the current limit holding current for the SC4626 to exit foldback current limit mode. figure 2 shows the typical current limit holding current decreasing rate over difer - ent output voltage. the SC4626 is capable of sustaining a indefnite short circuit without damage and will resume normal operation when the fault is removed. the fold - back current limit mode will be disabled during the soft-start. ? ? ? ? applications information en gnd c in v in v out c out l lx vout enable SC4626a vin r fb1 c ff r fb2 10k ? r en note: (1) r en is optional. (2) r fb2 =10k ? and c ff =10nf for standard design. 2 1 )1 ( fb out fb r v r ? = schematic of adjustable v out from SC4626a (std v out =1.0v) current limit holding current over vout 0 30 60 90 120 150 1.0 1.5 2.0 2.5 3.0 3.5 output voltage (v) current limit holding current (ma) t a = 25c v in = 5.0v v in = 3.6v www.semtech.com ? 2009 semtech corp. 6 SC4626 over-voltage protection in the event of a 5% over-voltage on the output, the pwm drive is disabled with lx pin foating. soft-start the soft-start mode is activated after vin reaches its uvlo and en signal is set high to enable the part. an over temperature shutdown event will also activate the soft start sequence. soft-start mode controls the maximum current during startup thus limiting in-rush current. the pmos current limit is stepped through four soft start levels of approximately 20%, 25%, 40%, & 00%. each step is maintained for 20s following internal reference start up of 20s giving the total nominal startup period of 00s. during startup, the chip operates in controlling the inductor current swings between 0a and current limit. if v out reaches 90% of the target within the frst 2 current levels, the chip continues in hysteretic mode till the end of the soft-start time period before switching to pwm mode. if v out does not reach 90% by the end of the second current limit level, soft start will continue to level 3 or level 4 till the output voltage reaches 96% and will then transition into pwm mode. after the full soft start time period, the SC4626 will switch into pwm mode operation regardless of the v out level. the SC4626 is capable of starting up into a pre-biased output. when the output is precharged by another supply rail, the SC4626 will not discharge the output during the soft start interval. shut down when the en pin voltage goes low, the SC4626 will run in shutdown mode, drawing less than a from the input power supply. the internal switches and bandgap voltage will be immediately turned of. inductor selection the SC4626 converter has internal loop compensation. the compensation is designed to work with a output flter corner frequency is less than 00khz over any operating condition, tolerance and bias efect. the corner frequency of output flter can be defned by the equation out c c l f ? s 2 1 values outside this range may lead to instability, malfunction, or out-of-specifcation performance. when choosing an inductor, it is important to consider the change in inductance with dc bias current. the inductor saturation current is specifed as the current at which the inductance drops a specifc percentage from the nominal value. this is approximately 30%. except for short-circuit or other fault conditions, the peak current must always be less than the saturation current specifed by the manufacturer. the peak current is the maximum load current plus one half of the inductor ripple current at the maximum input voltage. load and/or line transients can cause the peak current to exceed his level for short durations. maintaining the peak current below the inductor saturation specifcation keeps the inductor ripple current and the output voltage ripple at acceptable levels. manufacturers often provide graphs of actual inductance and saturation characteristics versus applied inductor current. the saturation characteristics of the inductor can vary signifcantly with core temperature. core and ambient temperatures should be considered when examining the core saturation characteristics. when the inductance has been determined, the dc resistance (dcr) must be examined. the efciency that can be achieved is dependent on the dcr of the inductor. the lower values give higher efciency. the rms dc current rating of the inductor is associated with losses in the copper windings and the resulting temperature rise of the inductor. this is usually specifed as the current which produces a 40?c temperature rise. most copper windings are rated to accommodate this temperature rise above maximum ambient. magnetic felds associated with the output inductor can interfere with nearby circuitry. this can be minimized by the use of low noise shielded inductors which use the minimum gap possible to limit the distance that magnetic felds can radiate from the inductor. however shielded inductors typically have a higher dcr and are thus less efcient than a similar sized non-shielded inductor. applications information (continued) www.semtech.com ? 2009 semtech corp. 7 SC4626 applications information (continued) tablef2bfCffrecommendedflfandfoutputfcapacitorsfforfvout=1.8vftof3.3v tablef2afCffrecommendedflfandfoutputfcapacitorsfforfvout=1.0vftof1.5v 2 grm188r60g106m murata 10uf,4.0v x5r,0603 1 grm21br60j226m murata 22uf,6.3v x5r,0805 lqm2hpn1r0mg0 murata 1.0uh, 69m ? (max) multilayer chip 2.5x2.0x1.0(mm) 1 grm219r60j106k murata 10uf,6.3v x5r,0805 1 grm21br60j226m murata 22uf,6.3v x5r,0805 mdt2520-cr1r0m toko 1.0uh, 80m ? (max) multilayer chip 2.5x2.0x1.0(mm) 1 grm21br60j106k murata 10uf,6.3v x5r,0805 1222as-h-2r2m toko 2.2uh, 120m ? (max) wire wound 2.5x2.0x1.2(mm) 1 grm21br60j226m murata 22uf,6.3v x5r,0805 1071as-1r0n toko 1.0uh, 40m ? (max) wire wound 2.8x3.0x1.5(mm) 1 grm21br60j106k murata 10uf,6.3v x5r,0805 1071as-2r2m toko 2.2uh, 60m ? (max) wire wound 2.8x3.0x1.5(mm) qty. part number vender description part number vender description output capacitor inductor a(1.0v),c(1.2v),e(1.28v),f(1.3v),h(1.5v) vout code (vout) 2 grm188r60g106m murata 10uf,4.0v x5r,0603 1 grm21br60j226m murata 22uf,6.3v x5r,0805 mdt2520-cr1r0m toko 1.0uh, 80m ? (max) multilayer chip 2.5x2.0x1.0(mm) 1 grm21br60j106k murata 10uf,6.3v x5r,0805 1222as-h-2r2m toko 2.2uh, 120m ? (max) wire wound 2.5x2.0x1.2(mm) 1 grm21br60j226m murata 22uf,6.3v x5r,0805 1071as-1r0n toko 1.0uh, 40m ? (max) wire wound 2.8x3.0x1.5(mm) 1 grm21br60j106k murata 10uf,6.3v x5r,0805 1071as-2r2m toko 2.2uh, 60m ? (max) wire wound 2.8x3.0x1.5(mm) qty. part number vender description part number vender description output capacitor inductor l(1.8v),y(2.5v),z(3.3v) vout code (vout) www.semtech.com ? 2009 semtech corp. 8 SC4626 applications information (continued) the SC4626 is compatible with small shielded chip inductors for low cost, low profle applications. the inductance roll of characteristic of chip inductor is worse resulting in high ripple current and increased output voltage ripple at heavy load operation. SC4626 has ocp peak inductor current threshold of .5a minimum, to support a dc load current, the inductor ripple current at a dc load current needs to be less than a. final inductor selection depends on various design considerations such as efciency, emi, size, and cost. table 2a and 2b list the manufacturers of recommended inductor and output capacitors options. chip inductors provide smaller footprint and height with lower efciency and increased output voltage ripple. transient load performance is equivalent to wire wound inductors. figure 3 shows the typical efciency curves for diferent inductors. efficiency 60% 65% 70% 75% 80% 85% 90% 95% 100% 0.0 0.2 0.4 0.6 0.8 1.0 output current (a) efficiency (%) v in = 5.0v v out = 3.3v t a =25c l=1071as-1r0n (33m ? _typ) l=1071as-2r2n (50m ? _typ) l=lqm2hp1r0mg0 (55m ? _typ) l=mdt2520-cr1r0m (60m ? _typ) figuref3fftypicalfefciencyfcurves (v in =5.0v,fv out =3.3v) c out fselectionf the internal voltage loop compensation in the SC4626 limits the minimum output capacitor value to 0f if using the inductor of 2.2h. this is due to its infuence on the the loop crossover frequency, phase margin, and gain margin. increasing the output capacitor above this minimum value will reduce the crossover frequency and provide greater phase margin. a total output capacintance should not exceed 30uf to avoid any start-up problems. for most typical applications, it is recommended to use output capacitance of 0uf to 22uf. when choosing output capacitors capacitance, verify the voltage derating efect from the capacitor vendors data sheet. capacitors with x7r or x5r ceramic dielectric are recom - mended for their low esr and superior temperature and voltage characteristics. y5v capacitors should not be used as their temperature coefcients make them unsuitable for this application. the output voltage droop due to a load transient is deter - mined by the capacitance of the ceramic output capacitor. the ceramic capacitor supplies the load current initially until the loop responds. within a few switching cycles the loop will respond and the inductor current will increase to match the required load. the output voltage droop during the period prior to the loop responding can be related to the choice of output capacitor by the relationship osc droop load out f v i c ? ? ? = 3 the output capacitor rms current ripple may be calculated from the equation ( ) ? ? ? ? ? ? ? ? ? ? ? ? = in osc out max in out rms cout v f l v v v i ) ( ) ( 3 2 1 table 3 lists the manufacturers of recommended output capacitor options. c in selection the SC4626 source input current is a dc supply current with a triangular ripple imposed on it. to prevent large input voltage ripple, a low esr ceramic capacitor is required. a minimum value of 4.7f should be used. it is important to consider the dc voltage coefcient charac - teristics when determining the actual required value. to estimate the required input capacitor, determine the acceptable input ripple voltage and calculate the minimum value required for c in from the equation osc out in out in out in f esr i v v v v v c ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? = 1 the input capacitor rms ripple current varies with the www.semtech.com ? 2009 semtech corp. 9 SC4626 input and output voltage. the maximum input capacitor rms current is found from the equation ? ? ? ? ? ? ? ? ? = in out in out rms cin v v v v i 1 ) ( the input voltage ripple and rms current ripple are at maximum when the input voltage is twice the output voltage or 50% duty cycle. the input capacitor provides a low impedance loop for the edges of pulsed current drawn by the pmos switch. low esr/esl x5r ceramic capacitors are recommended for this function. to minimise stray inductance ,the capacitor should be placed as closely as possible to the vin and gnd pins of the SC4626. manufacturer part nunber value (f) type rated voltage (vdc) value at 3.3v (f) dimensions lxwxh (mm) murata grm21br61a106k 00% x5r 0 4.42 2.0x.25x.25 (eia:0805) murata grm21br71a106k 00% x7r 0 4.88 2.0x.25x.25 (eia:0805) murata grm21br60j106k 00% x5r 6.3 4.05 2.0x.25x.25 (eia:0805) murata grm21br70j106k 00% x7r 6.3 4.9 2.0x.25x.25 (eia:0805) murata grm21br60j226m 2220% x5r 6.3 6.57 2.0x.25x.25 (eia:0805) table 3 C recommended capacitors applications information (continued) www.semtech.com ? 2009 semtech corp. 20 SC4626 pcb layout considerations the layout diagram in figure 4 shows a recommended pcb top-layer and bottom layer for the SC4626 and supporting components. fundamental layout rules must be followed since the layout is critical for achieving the performance specifed in the electrical characteristics table. poor layout can degrade the performance of the dc-dc converter and can contribute to emi problems, ground bounce, and resistive voltage losses. poor regulation and instability can result. the following guidelines are recommended when developing a pcb layout: the input capacitor, c in should be placed as close to the vin and gnd pins as possible. this capacitor provides a low impedance loop for the pulsed currents present at the buck converters input. use short wide traces to connect as closely to the ic as possible. this will minimize emi and input voltage ripple by localizing the high frequency current pulses. keep the lx pin traces as short as possible to minimize pickup of high frequency switching edges to other parts of the circuit. c out and l should be connected as close as possible between the lx and gnd pins, with a direct return to the gnd pin from c out . route the output voltage feedback/sense path away from inductor and lx node to minimize noise and magnetic interference. use a ground plane referenced to the SC4626 gnd pin. use several vias to connect to the component side ground to further reduce noise and interference on sensitive circuit nodes. if possible, minimize the resistance from the vout and gnd pins to the load. this will reduce the voltage drop on the ground plane and improve the load regulation. and it will also improve the overall efciency by reducing the copper losses on the output and ground planes. . 2. 3. 4. 5. applications information (continued) figure 4 recommended pcb top & bottom layer layout gnd vout l c in c out u1 vin gnd en (a) top layer (b) bottom layer www.semtech.com ? 2009 semtech corp. 2 SC4626 semtech corporation power management products division 200 flynn road, camarillo, ca 930 2 phone: (805) 498-2 fax: (805) 498-3804 www.semtech.com contact information outline drawing C sot23-5 land pattern C sot23-5 .110 bsc .037 bsc detail aaa c seating plane c ccc c 2x n/2 tips 2x e/2 5 see detail a1 a a2 bxn d a .008 1 2 n e1 e d .060 .114 .063 .118 .010 - 5 a 0.20 1.60 3.00 2.80 bsc 0.95 bsc .069 1.50 2.90 .020 0.25 1.75 0.50 - ei l (l1) c 01 0.25 plane gage h 2.80 .110 bbb c a-b d a b e 0 .008 - .004 .012 .003 (.024) .018 - .035 .000 .035 - - .045 0.10 0.20 10 0 - 10 1.15 (0.60) 0.45 .024 .009 0.30 0.08 .057 .051 .006 0.00 .90 0.90 0.22 0.60 - 0.15 1.45 1.30 - - 1.90 bsc .075 bsc dimensions "e1" and "d" do not include mold flash, protrusions datums and to be determined at datum plane or gate burrs. controlling dimensions are in millimeters (angles in degrees). notes: 1. 3. 2. -a- -b- -h- dimensions inches l1 aaa bbb ccc 01 n dim e e1 l e e1 c d a a2 b a1 min nom millimeters nom max min max side view dimensions inches y z dim g p x c millimeters p (c) z y g .043 .141 .055 (.098) .037 .024 1.40 (2.50) 0.95 0.60 1.10 3.60 x dimensions inches y z dim g p x c millimeters this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 1. |
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