lx1736 p roduction d ata s heet microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 1 www. microsemi . com 5v 1.25a 1.0mhz pwm/pfm step down regulator tm ? copyright ? 2007 rev. 1.1., 11/25/2008 description the lx1736 operates as a current mode pwm buck regulator that switches to pfm mode under light loads. the entire regulator function is implemented with only a few, low- cost external components. the lx1736 responds quickly to dynamic load changes using a high bandwidth error amplifier and internal compensation. tight output voltage regulation is maintained with the temperature compensated 800mv, bandgap reference achieving +/-3.5% regulation tolerance for all line, load and thermal conditions. the output voltage is easily programmed, from 800mv to 90% of v in with two external resistors the regulator is capable of providing an output load current up to 1.25a and has no minimum load current requirement for stable operation. current limit senses on a cycle-by cycle basis to protect the switch. power conversion efficiency is maximized with pfm mode of operation and low regulator quiescent current. the lx1736 operational supply voltage range covers 4.0v to 6.0v, features include: power on delay; soft start to limit inrush currents and thermal shutdown during fault conditions. the 6-pin jedec mo-229 package provides a small form factor and low profile at 3x3x1mm with excellent power dissipation capability on surface mount pcb?s. important: for the most current data, consult microsemi ?s website: http://www.microsemi.com key features ? few external components ? 800mv internal reference ? tight regulation over line, load and temperature ? 4.5v to 5.5v input range ? internal soft start controls inrush current ? high efficiency ? low quiescent current, 600 a ? fully fault protected ? thin mo-229, 6-pin package applications ? point of load regulation ? dsp, asic and core voltage supplies ? hard disk drives ? set top boxes ? rohs compliant product product highlight figure 1 ? lx1736 application circuit and typical efficiency performance efficiency @ v in= 5v, vo=1.25v (lower) vo=3.3v (upper) 25% 35% 45% 55% 65% 75% 85% 95% 1 10 100 1000 output current, ma package order info ld plastic mlpd 6 pin 3mm x 3mm t a ( c) rohs compliant / pb-free 0 to 125 lx1736cld note: available in tape & reel. append the letters ?tr? to the part number. (i.e. LX1736CLD-TR) package marking msc xxxx 3049 l l x x 1 1 7 7 3 3 6 6
lx1736 p roduction d ata s heet microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 2 www. microsemi . com 5v 1.25a 1.0mhz pwm/pfm step down regulator tm ? copyright ? 2007 rev. 1.1., 11/25/2008 absolute maximum ratings input voltage (vcc or vp wr) ..................................................................... -0 .3v to 7.0v sw to gnd........................................................................................ -0.3v to (v in + 0.3v) vfb to gnd................................................................................................... -0.3v to +2v sw peak current .....................................................................................i nternally limited junction operating temperat ure range ........................................................0c to +125c storage temperature rang e, ta..................................................................-65 c to 150c maximum junction te mperatur e ............................................................................... 150c package peak temp. for solder reflow ( 40 seconds max. expos ure)........... 260c (+0, -5) note: exceeding these ratings could cause damage to the device. all voltages are with respect to ground. currents are positive into, negative out of specified terminal . thermal data ld plastic mlp 3x3mm mo-229, 6-pin thermal resistance - junction to c ase , jc 4 c/w thermal resistance - junction to a mbient , ja 25 to 50 c/w junction temperature calculation: t j = t a + (p d x ja ). the ja numbers are guidelines for the thermal performa nce of the device/pc-board system. all of the above assume no ambient airflow. package pin out fb g nd sw vpwr vcc nc 1 2 3 4 5 6 ld p ackage (top view) rohs / pb-free 100% matte tin pin finish functional pin description name pin # description vcc 5 unregulated supply voltage input, ranging from +4v to 6.0v for internal analog control circuitry. vpwr 4 unregulated supply voltage input (+4v to 6.0v), high current path, supplies pmosfet drain of pwm switch. fb 1 feedback input for setting programming output voltage. gnd 2 circuit ground for ic analog circuitry and high fr equency gate drive bias, exposed pad area on bottom of package may be connected to ground or left floating. sw 3 inductor and commutation diode connection point. con nects to internal pmosfet source of pwm switch output. recommended operating conditions lx1736 parameter symbol min typ max unit ` input operating voltage range v in 4.5 5.5 v continuous output current range i out 0 0.9 a output voltage range v out 0.8 80% of v in v operating junction temperature t j 0 125 c d d e e v v i i c c e e d d a a t t a a
lx1736 p roduction d ata s heet microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 3 www. microsemi . com 5v 1.25a 1.0mhz pwm/pfm step down regulator tm ? copyright ? 2007 rev. 1.1., 11/25/2008 electrical characteristics specifications are guaranteed over the junctio n temperature range of: 0c < t < 125c for vin = 4.5v to 5.5v (unless noted othe rwise), not all of these parameters are production tested but are assure d by design, characterization an d correlation wi th statistical process controls.. typical values are at ta=23c. lx1736 parameter symbol test conditions min typ max units feedback threshold v fbt 4.0v < vin < 6.0v 772 800 828 mv feedback input current i fb-in v fb = v fbt + 10mv 75 na pwm frequency f op-pwm pwm mode 800 1450 khz pfm mode transition io-pfm pfm mode 80 ma minimum dc output current i out 0 ma maximum dc output current i outmax t j 70 ? c 1.25 or 0.7/duty cycle whichever is less a maximum duty cycle d max i sw = i out max 80 % closed loop load regulation v out load reg 10ma1.1v, i out 150ma 70 % quiescent current i q v fb = v fbt + 10mv 600 900 a p-channel switch on resistance r ds(on) i sw = 0.9a 0.375 ? peak current at switch pin (not dc current) 1.1 p-channel switch current limit i sw cl t j 70 ? c 1.4 a p-channel switch leakage i sw lkg v fb = v fbt + 10mv 5 a soft start, vout slew rate v o-sr initial power on or after a short circuit, c out = 20f 21 50 v/ms thermal shutdown t sd (silicon temperature) 135 150 c dc average in-rush current at vcc and vpwr (summed) i inrush v in ramping from 0v to 5v having a slew rate of 0.1v/s min to 0.5v/us max and c out = 20f 550 ma output voltage overshoot (from either removal of a short circuit condition from v out or applied power during start up) v o os applied power v in ramp rate of 0.1v/s min to 0.5v/us max 5 % output voltage response to dynamic load change v o os output load current change from 100ma to 700ma or 700ma to 100ma, transition time <100ns -5 5 % circuit output capacitance c out closed loop stability 20 f e e l l e e c c t t r r i i c c a a l l s s
lx1736 p roduction d ata s heet microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 4 www. microsemi . com 5v 1.25a 1.0mhz pwm/pfm step down regulator tm ? copyright ? 2007 rev. 1.1., 11/25/2008 application support cout vout vin lx1736 ground cout cout cout diode vpwr vin n/c sw gnd fb inductor rf rf cin pcb layout considerations 1- maintain separate traces leadi ng from the decoupling capacitor, c in , to the supply input pins of the ic for vcc and vpwr. this ensures that the noise and voltage drops associated with the high di/dt pulses from the pwm switching are minimized for the internal control circuitry of the ic. 2- diode ground shou ld return to c out ground with minimum physical distance before joining the ic ground connection. 3- feed back resistor return path to ground should be located closely to the ic pin 2 to avoid v out offsets induced by ground drops and noise. a a p p p p l l i i c c a a t t i i o o n n
lx1736 p roduction d ata s heet microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 5 www. microsemi . com 5v 1.25a 1.0mhz pwm/pfm step down regulator tm ? copyright ? 2007 rev. 1.1., 11/25/2008 simplified block diagram vpwr cl clock and ramp pwm ea gnd bg ref 800mv ovp 920mv ref s r fb sw lx1736 vcc uvlo bias application performance dynamic load change response ch1 = vout ac coupled ch2 = load switch ch4 = output current, 100ma to 750ma v in =5v, l=3.3uh, c out = 20uf a a p p p p l l i i c c a a t t i i o o n n
lx1736 p roduction d ata s heet microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 6 www. microsemi . com 5v 1.25a 1.0mhz pwm/pfm step down regulator tm ? copyright ? 2007 rev. 1.1., 11/25/2008 start-up inrush current control ch1 = sw pin ch2 = vout @ 3.32v ch4 = input current v in =5v, no output load, c out = 20uf vout response to short circuit removal ch1 = vout programmed at 1.2v ch2 = short ckt duration ch4 = output current c out = 20uf a a p p p p l l i i c c a a t t i i o o n n
lx1736 p roduction d ata s heet microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 7 www. microsemi . com 5v 1.25a 1.0mhz pwm/pfm step down regulator tm ? copyright ? 2007 rev. 1.1., 11/25/2008 package dimensions ld mo-229 6-pin plastic 3 x 3 x .9 mm d e l1 l e d2 e2 b k pin 1 id a a1 note: 1. dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006?) on any side. lead dimension shall not include solder coverage. 2. exposed heatsink pad on bottom may be left floating or connected to ground. m illimeters i nches dim min max min max a 0.80 1.00 0.031 0.039 a1 0.00 0.05 0.000 0.002 k 0.20 min 0.008 min e 0.95 bsc 0.037 bsc l 0.30 0.50 0.012 0.020 b 0.30 0.45 0.012 0.018 d2 1.90 2.40 0.075 0.094 e2 1.15 1.65 0.045 0.065 d 3.00 bsc 0.118 bsc e 3.00 bsc 0.118 bsc l1 0.00 0.15 0.000 0.006 notes production data ? information contained in this document is proprietary to microsemi and is current as of publication date. this document may not be modified in any way without the express written consent of microsemi. product processing does not necessarily include testing of all parameters. micros emi reserves the right to change the configuration and performance of the product and to discontinue product at any time. m m e e c c h h a a n n i i c c a a l l
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