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| august 27, 2010 power management 2.5mhz, 1.5a synchronous step down regulator sc189 www.semtech.com 1 typical application circuit gnd en c in 10f v in 2.9v to 5.5v v out 1.20v/1.5a c out 22f l 1h lx vout sc189c vin features v in range: 2.9 C 5.5v v out options: 1.0 - 3.3v up to 1.5a output current ultra-small footprint, <1mm height solution 2.5mhz switching frequency efciency up to 93% low output noise across load range excellent transient response start up into pre-bias output 100% duty-cycle low dropout operation <1a shutdown current internal soft start input under-voltage lockout output over-voltage, current limit protection over-temperature protection adjustable output voltage available in sot23-5 package and 2mm x 2mm x 0.6mm thermally enhanced mlpd-ut6 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 sc189 is a high efciency, synchronous step-down regulator providing up to 1.5a output current in either an ultra-small 2mm x 2mm, low profle package or a low cost 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 1.0 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. total footprint of 25mm 2 can be achieved - making the sc189 the ideal solution for high density systems. solution height of <1mm is also possible. 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. 100% duty-cycle provides 360mv dropout voltage at 1.5a which extends the minimum input voltage for 2.5v and 3.3v outputs. excellent transient response is achieved with no external compensation components. the sc189 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 1a. the sc189 is available in sot23-5 and a thermally enhanced 2mm x 2mm x 0.6mm mlpd-ut6 package. sc189 l chip c in 0603 c out 0805 total pcb area ~25mm 2 actual size
www.semtech.com ? 2009 semtech corp. 2 sc189 pin confguration ordering information marking information device package & description sc189xultrt (2)(3)(4) 2mm x 2mm x 0.6mm mlpd-ut6 sc189xsktrt 2)(3)(4) sot23-5 sc189xevb (5) evaluation board for mlpd-ut6 - standard size (i.e., wire wound inductor) sc189xevb-1 (5) evaluation board for mlpd-ut6 - small size (i.e., chip inductor) sc189xevb-2 (5) evaluation board for sot23-5 - standard size (i.e., wire wound inductor) sc189xevb-3 (5) evaluation board for sot23-5 - small size (i.e., chip inductor) notes: (1) measured in free convection, mounted on 10mm x 10mm, 2 layer fr4 pcb shown in fgure 7 ( for mlpd-ut6 package) and fgure 8 ( for sot23-5 package) with copper of 1oz 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 1 for the code. for example, the device number for vout= 1.20v is sc189cultrt. (5) x is the code of the output voltage. see table 1 for the code. for example, the evb for mlpd-ut6 package with vout= 1.20v is sc189cevb (standard size) or sc189cevb-1 (small size). table 1: available output voltages code for mlpd-ut6 code for sot23-5 vout (1) a a 1.00 b b 1.10 c c 1.20 e not available 1.28 f not available 1.30 h h 1.50 l l 1.80 n not available 2.00 t y 2.50 not available v 2.70 z z 3.30 notes: (1) contact factory for unavaliable output voltage options. 2mmfxf2mmfxf0.6mmfmlpd-ut6 ja f=f60c/w (1) top view nc 1 2 3 6 5 4 en vin vout gnd lx t marking for 2mm x 2mm mlpd-ut 6 lead package: x = code of the output voltage (example: c for vout=1.20v) oyw = pin 1 and datecode (reference package marking design guidelines, appendix a) flx 1 2 3 5 4 vin gnd en lx vout top view sot23-5 ja f=f90c/w (1) 189 x top mark bottom mark marking for sot23, 5 lead package: x = code of the output voltage (example: c for vout=1.20v) yyww = datecode (example: 0852) www.semtech.com ? 2009 semtech corp. 3 sc189 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: (1) measured in free convection, mounted on 10mm x 10mm, 2 layer fr4 pcb shown in fgure 7 ( for mlpd-ut6 package) and fgure 8 ( for sot23- 5 package) with copper of 1oz for each layer. (2) tested according to jedec standard jesd22-a114-b. (3) for sot23-5 package, the limit of the maximum power dissiption shown in fgure 2 may reduce the maximum output current. electrical characteristics recommended operating conditions vin supply voltage 2.9 to 5.5v maximum output current (3) 1.5a thermal resistance, junction to ambient (1) mlpd-ut6 package 60c/w sot23-5 package 90c/w operating junction temperature -40 to +125 ? c maximum junction temperature +150c storage temperature range -65 to +150 c thermal information absolute maximum ratings vin supply voltage -0.3 to 6.0v lx voltage .. -1 to v in +1v, -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, c in =10f, c out =10f; l=2.2h; -40c www.semtech.com ? 2009 semtech corp. 6 sc189 typical characteristics ( continued ) circuit conditions: c in = 10uf/6.3v; c out = 10uf/6.3v for l=2.2uh; c out = 22uf/6.3v for l=1uh. unless otherwise noted, l= 2.2uh (toko: 1071as-2r2m) and sc189 in mlpd-ut6 package. efciencyfvs.floadfcurrentf(v out =1.5v,fsot23-5) totalflossfvs.floadfcurrentf(v out =1.5v,fsot23-5) efciencyfvs.floadfcurrentf(v out =3.3v,fsot23-5) efciencyfvs.floadfcurrentf(sot23-5) efciencyfvs.floadfcurrentf(sot23-5) efficiency 60% 65% 70% 75% 80% 85% 90% 95% 100% 0.0 0.3 0.6 0.9 1.2 1.5 output current (a) efficiency (%) v out = 1.50v t a =25c v in = 5.0v v in = 3.3v efficiency 60% 65% 70% 75% 80% 85% 90% 95% 100% 0.0 0.3 0.6 0.9 1.2 1.5 output current (a) efficiency (%) v out = 3.30v t a =25c v in = 5.0v v in = 4.0v efficiency 60% 65% 70% 75% 80% 85% 90% 95% 100% 0.0 0.3 0.6 0.9 1.2 1.5 output current (a) efficiency (%) v in = 5.0v v out = 1.0v t a =25c l=1071as-1r0 (33m ? _typ) l=1071as-2r2 (50m ? _typ) l=lqm2hpn1r0mg0 (55m ? _typ) l=mdt2520-cr1r0 (60m ? _typ) efficiency 60% 65% 70% 75% 80% 85% 90% 95% 100% 0.0 0.3 0.6 0.9 1.2 1.5 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) losses 0 200 400 600 800 0.0 0.3 0.6 0.9 1.2 1.5 output current (a) loss (mw) v out = 3.30v t a =25c v in = 5.0v v in = 4.0v losses 0 200 400 600 800 0.0 0.3 0.6 0.9 1.2 1.5 output current (a) loss (mw) v out = 1.50v t a =25c v in = 5.0v v in = 3.3v totalflossfvs.floadfcurrentf(v out =3.3v,fsot23-5) www.semtech.com ? 2009 semtech corp. 7 sc189 typical characteristics ( continued ) linefregulation rdson (p & n) variation over line -10% -5% 0% 5% 10% 15% 20% 25% 30% 2.5 3.0 3.5 4.0 4.5 5.0 5.5 input voltage (v) variation i lx = 100ma t a = 25c 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) variation over temperature -20% -15% -10% -5% 0% 5% 10% 15% 20% -40 -15 10 35 60 85 ambient temperature (c) variation 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) fvariationfvs.finputfvoltage r ds(on) fvariationfvs.ftemperature switchingffrequencyfvs.finputfvoltage switchingffrequencyfvs.ftemperature circuit conditions: c in = 10uf/6.3v; c out = 10uf/6.3v for l=2.2uh; c out = 22uf/6.3v for l=1uh. unless otherwise noted, l= 2.2uh (toko: 1071as-2r2m) and sc189 in mlpd-ut6 package. www.semtech.com ? 2009 semtech corp. 8 sc189 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 dropout voltage of 100% duty cycle operation (mlp) 0 50 100 150 200 250 300 350 400 450 500 0.0 0.3 0.6 0.9 1.2 1.5 output current (a) dropout voltage (mv) package: mlpd-ut6 t a = 25c l= mdt2520-cr1r0m (dcr= 80m ? _max) l= 1071as-1r0 (dcr=40m ? _max) loadfregulationf (v out =1.5v) 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 0.3 0.6 0.9 1.2 1.5 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 0.3 0.6 0.9 1.2 1.5 output current (a) load regulation v in = 5.0v v in = 4.0v v out = 3.30v t a =25c loadfregulationf (v out =3.3v) circuit conditions: c in = 10uf/6.3v; c out = 10uf/6.3v for l=2.2uh; c out = 22uf/6.3v for l=1uh. unless otherwise noted, l= 2.2uh (toko: 1071as-2r2m) and sc189 in mlpd-ut6 package. dropoutfvoltagefinf100%fdutyfcyclefoperation dropout voltage of 100% duty cycle operation (sot23 -5) 0 50 100 150 200 250 300 350 400 450 500 0.0 0.3 0.6 0.9 1.2 1.5 output current (a) dropout voltage (mv) package: sot23-5 t a = 25c l= mdt2520-cr1r0m (dcr= 80m ? _max) l= 1071as-2r2 (dcr=60m ? _max) www.semtech.com ? 2009 semtech corp. 9 sc189 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) 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) 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 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 =1.5a 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 =1.5a 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 typical waveforms circuit conditions: v out =1.5v (sc189hultrt); l= 2.2uh (toko: 1071as-2r2m); c in = c out = 10uf/6.3v (murata: grm21br60j106k). www.semtech.com ? 2009 semtech corp. 10 sc189 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 ? 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 ? 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 =1.5v (sc189hultrt); l= 2.2uh (toko: 1071as-2r2); c in = c out = 10uf/6.3v (murata: grm21br60j106k). www.semtech.com ? 2009 semtech corp. 11 sc189 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 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 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 =1.5a 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 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 =2.2 ? typical waveforms ( continued) circuit conditions: v out =3.3v (sc189zultrt); l= 2.2uh (toko: 1071as-2r2); c in = c out = 10uf/6.3v (murata: grm21br60j106k). www.semtech.com ? 2009 semtech corp. 12 sc189 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 =2.2 ? 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 (sc189zultrt); l= 2.2uh (toko: 1071as-2r2); c in = c out = 10uf/6.3v (murata: grm21br60j106k). www.semtech.com ? 2009 semtech corp. 13 sc189 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) 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) 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 v out 10mv/div v lx 2v/div i lx 1a/div 500ns/div output voltage ripple (v out =1.0v) v in =3.3v i out =1.5a 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 =1.5a 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 typical waveforms ( continued) circuit conditions: v out =1.0v (sc189aultrt); l= 1uh (murata: lqm2hpn1r0ng0l); c in = 10uf/6.3v; c out = 22uf/6.3v (murata: grm21br60j226m). www.semtech.com ? 2009 semtech corp. 14 sc189 pin descriptions pin # (mpld-ut6) pin # (sot23-5) pin name pin function 1 not available nc no connection. 2 3 en enable pin. when connected to logic high or tied to vin pin, the sc189 is on. when con - nected to logic low, the device enters shutdown and consumes less than 1a of current. the enable pin has a 1 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 un - dervoltage lockout. 3 1 vin input power supplies. powers the internal circuitry and is connected to the source of high- side p channel mosfet. 4 5 lx switching node - connect an inductor between this pin and the output capacitor. 5 2 gnd ground connection. 6 4 vout output voltage sense pin. t not available thermal pad thermal pad for heatsinking purposes. this pad is not connected internally. connect it to gnd plane. www.semtech.com ? 2009 semtech corp. 15 sc189 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. 16 sc189 detailed description the sc189 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 sc189 is designed for fxed output voltage. there are some options for preset output voltage shown in table 1. if the voltage desired is not shown in the table 1, it can be programmed via an external resistor di - vider. there will be typical 1ua current fowing into the vout pin. the typical schematic of adjustable output voltage option from the part with standard 1.0v, the sc189a, is shown in figure 1. the c ff is needed for main - tain 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 1. to simplify the design, it is recommended to program the desired output voltage from standard 1.0v as shown in figure 1 with a proper c ff calculated from the equation shown above. for programming the output voltage from other standard voltage, the r fb1 , r fb2 and c ff need to be adjusted to meet the equation shown above. maximum power dissiption of sot23-5 package the maximum power dissiption for junction tempera - ture of less than 125c on sot23-5 package is shown in fgure 2. the curve is drawn based on the ja of 90c/w which is measured in free convection, mounted on 10mm x 10mm, 2 layer fr4 pcb shown in fgure 8 with copper of 1oz for each layer. the maximum power dissiption may limit the maximum output current over temperature. the fgure 3 and fgure 4 show the typi - cal maximum output current for t j 125c over tem - perature of v in =5.0v and v in =3.3v, respectively. if using inductor with higher loss (i.e., chip inductor), due to the higher board temperature, the ja will be a little bit higher. protection features the sc189 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 sc189 if the junction temperature exceeds 160c. during thermal shutdown, the on-chip power devices are disabled with the lx output foating. when the die temperature drops by 10c, 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 sc189 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 ? ? ? ? applications information en gnd c in v in v out c out l lx vout enable sc189a 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 sc189a (std v out =1.0v) www.semtech.com ? 2009 semtech corp. 17 sc189 the current limit holding current for the sc189 to exit foldback current limit mode. figure 5 shows the typical current limit holding current decreasing rate over difer - ent output voltage. the sc189 is capable of sustaining an indefnite short circuit without damage and will resume normal operation when the fault is removed. the foldback current limit mode will be disabled during the soft-start. over-voltage protection i n the event of a 15% 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%, & 100%. each step is maintained for 20s following internal reference start up of 20s giving the total nominal startup period of 100s. 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 sc189 will switch into pwm mode operation regardless of the v out level. the sc189 is capable of starting up into a pre-biased output. when the output is precharged by another supply rail, the sc189 will not discharge the output during the soft start interval. shut down when the en pin voltage goes low, the sc189 will run in shutdown mode, drawing less than 1a from the input power supply. the internal switches and bandgap voltage will be immediately turned of. inductor selection the sc189 converter has internal loop compensation. the applications information (continued) figure 3 typical maximum output current over temperature of sot23-5 package v in 5.v figure typical maximum output current over temperature of sot23-5 package v in 3.3v maximum output current for t j ? 125c 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 ambient temperature (c) output current (a) v in = 5.0v ? ja = 90c/w v out =1.2v v out =2.5v v out = 3.3v maximum output current for t j ? 125c 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 ambient temperature (c) output current (a) v in = 3.3v ? ja = 90c/w v out =1.2v v out =2.5v maximum power dissiption for t j ? 125c sot23-5 package 0 300 600 900 1200 1500 -40 -25 -10 5 20 35 50 65 80 95 110 125 ambient temperature (c) power dissiption (mw) ? ja = 90c/w 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. 18 sc189 applications information (continued) tablef2bfCffrecommendedflfandfoutputfcapacitorsfforfvout=1.8vftof3.3v tablef2afCffrecommendedflfandfoutputfcapacitorsfforfvout=1.0vftof1.5v description vender part number description vender part n umber qty. 2.2uh, 60m ? (max) wire wound 2.8x3.0x1.5(mm) toko 1071as-2r2n 10uf,6.3v x5r,0805 murata grm21br60j106k 1 1.0uh, 40m ? (max) wire wound 2.8x3.0x1.5(mm) toko 1071as-1r0n 22uf,6.3v x5r,0805 murata grm21br60j226m 1 22uf,6.3v x5r,0805 murata grm21br60j226m 1 10uf,6.3v x5r,0805 murata grm219r60j106k 1 22uf,6.3v x5r,0805 murata grm21br60j226m 1 10uf,4.0v x5r,0603 murata grm188r60g106m 2 output capacitor toko 1.0uh, 80m ? (max) multilayer chip 2.5x2.0x1.0(mm) vout code (vout) a(1.0v),b(1.1v),c(1.2v),e(1.28v),f( 1.3v),h(1.5v) murata lqm2hpn1r0mg0 inductor 1.0uh, 69m ? (max) multilayer chip 2.5x2.0x1.0(mm) mdt2520-cr1r0m description vender part number description vender part n umber qty. 2.2uh, 60m ? (max) wire wound 2.8x3.0x1.5(mm) toko 1071as-2r2n 10uf,6.3v x5r,0805 murata grm21br60j106k 1 1.0uh, 40m ? (max) wire wound 2.8x3.0x1.5(mm) toko 1071as-1r0n 22uf,6.3v x5r,0805 murata grm21br60j226m 1 22uf,6.3v x5r,0805 murata grm21br60j226m 1 10uf,4.0v x5r,0603 murata grm188r60g106m 2 output capacitor 1.0uh, 80m ? (max) multilayer chip 2.5x2.0x1.0(mm) toko mdt2520-cr1r0m inductor vout code (vout) l(1.8v),n(2.0v),t(y)(2.5v),v(2.7v), z(3.3v) www.semtech.com ? 2009 semtech corp. 19 sc189 applications information (continued) compensation is designed to work with a output flter corner frequency of less than 100khz 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. the sc189 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. sc189 has ocp peak inductor current threshold of 2.0a minimum, to support 1.5a dc load current, the inductor ripple current at 1.5a dc load current needs to be less than 1a. 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. 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 6 shows the typical efciency curves for diferent inductors. efficiency 60% 65% 70% 75% 80% 85% 90% 95% 100% 0.0 0.3 0.6 0.9 1.2 1.5 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) figuref6fftypicalfefciencyfcurves (v in =5.0v,fv out =3.3v) c out fselection the internal voltage loop compensation in the sc189 limits the minimum output capacitor value to 10f 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 10uf to 22uf. when choosing output www.semtech.com ? 2009 semtech corp. 20 sc189 capacitors capacitance, verify the voltage derating efect from the capacitor vendors data sheet. capacitors with x7r or x5r ceramic dielectric are recommended 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 determined 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 calcu - lated 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 sc189 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 applications information (continued) the input capacitor rms ripple current varies with the 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 sc189. manufacturer part nunber value (f) type rated voltage (vdc) value at 3.3v (f) dimensions lxwxh (mm) murata grm21br61a106k 1010% x5r 10 4.42 2.0x1.25x1.25 (eia:0805) murata grm21br71a106k 1010% x7r 10 4.88 2.0x1.25x1.25 (eia:0805) murata grm21br60j106k 1010% x5r 6.3 4.05 2.0x1.25x1.25 (eia:0805) murata grm21br70j106k 1010% x7r 6.3 4.91 2.0x1.25x1.25 (eia:0805) murata grm21br60j226m 2220% x5r 6.3 6.57 2.0x1.25x1.25 (eia:0805) table 3 C recommended capacitors www.semtech.com ? 2009 semtech corp. 21 sc189 figuref7ffrecommendedfpcbftopf&fbottomflayerf layoutfforfmlpd-ut6f2x2fpackage pcb layout considerations the layout diagram in fgure 7 and fgure 8 shows a recommended pcb for mlpd-ut6 2x2 and sot23-5 package, respectively. 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 sc189 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. 1. 2. 3. 4. 5. applications information (continued) (a)ftopflayerfforfmlpd-ut6f2x2fpackage (b)fbottomflayerfforfmlpdf2x2fpackage vin gnd gnd vout en l c in c out u1 gnd gnd figuref8ffrecommendedfpcbftopf&fbottomflayerf layoutfforfsot23-5fpackage (a)ftopflayerfforfsot23-5fpackage (b)fbottomflayerfforfsot23-5fpackage gnd vout l c in c out u1 vin gnd en www.semtech.com ? 2009 semtech corp. 22 sc189 outline drawing C 2x2 mlpd-ut6 land pattern C 2x2 mlpd-ut6 d e a a1 d1 e1 .061 .035 .026 .031 0.80 0.65 0.90 1.55 .071 .067 1.70 1.80 e bxn .075 .079 .083 1.90 2.00 2.10 d1 e1 (laser mark) indicator pin 1 1 n 2 min aaa bbb b e l n d a1 a2 a dim millimeters nom dimensions max nom inches min max a2 lxn notes: controlling dimensions are in millimeters (angles in degrees). coplanarity applies to the exposed pad as well as terminals. 2. 1. .003 .007 .075 6 .010 .079 .000 .018 (.006) 0.08 0.25 6 .012 .083 0.18 1.90 .024 .002 0.00 0.45 2.10 0.30 2.00 0.05 0.60 (0.1524) .004 0.10 0.50 bsc .020 bsc 0.25 .010 .018 .014 0.35 0.45 aaa c seating plane a bbb c a b b e c - - - - y h k 1. controlling dimensions are in millimeters (angles in degrees). this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. .031 .067 0.80 1.70 .106 .020 .012 .030 2.70 0.30 0.75 0.50 (.077) .047 1.20 (1.95) notes: 2. thermal vias in the land pattern of the exposed pad shall be connected to a system ground plane. functional performance of the device. failure to do so may compromise the thermal and/or inches dimensions g k h x y p z c dim millimeters (c) g z p x r .006 0.15 r 3. www.semtech.com ? 2009 semtech corp. 23 sc189 outline drawing C sot23-5 land pattern C sot23-5 controlling dimensions are in millimeters (angles in degrees). 1. y g (c) this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 2. dimensions y z dim g p x c millimeters p z 1.40 (2.50) 0.95 0.60 1.10 3.60 x www.semtech.com ? 2009 semtech corp. 24 sc189 ? semtech 2010 all rights reserved. reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. the information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. no liability will be accepted by the publisher for any consequence of its use. publication thereof does not convey nor imply any license under patent or other industrial or intellectual property rights. semtech assumes no responsibility or liability whatsoever for any failure or unexpected operation resulting from misuse, neglect improper installation, repair or improper handling or unusual physical or electrical stress including, but not limited to, exposure to parameters beyond the specifed maximum ratings or operation outside the specifed range. semtech products are not designed, intended, authorized or warranted to be suitable for use in life-support applications, devices or systems or other critical applications. inclusion of semtech products in such ap - plications is understood to be undertaken solely at the customers own risk. should a customer purchase or use semtech products for any such unauthorized application, the customer shall indemnify and hold semtech and its ofcers, em - ployees, subsidiaries, afliates, and distributors harmless against all claims, costs damages and attorney fees which could arise. semtech corporation power management products division 200 flynn road, camarillo, ca 93012 phone: (805) 498-2111 fax: (805) 498-3804 www.semtech.com contact information |
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