1 lt13 0 9 the lt ? 1309 is a 500khz micropower dc/dc converter for flash memory. the regulator features burst mode tm operation with a 0.5a, 300mv switch, enabling 85% efficiency at the fixed 12v output. high frequency opera- tion permits the use of small value, and therefore small size, surface mount inductors and capacitors. the LT1309 comes in an 8-lead so package allowing extremely compact pc board layouts. these features make the device attractive for pcmcia cards, cellular phones and other applications where pc board space is limited. quiescent current is 650 m a decreasing to 9 m a when the part shuts down. the device includes a soft start feature which limits supply current transients during turn-on. the LT1309 contains a vpp valid comparator with a logic output that goes low when the output voltage is ready to program 12v flash memory. this comparator simplifies the interface to external control logic. 500khz micropower dc/dc converter for flash memory s f ea t u re d u escriptio n 60ma output current at 12v from 3v or 5v supply n shutdown to 9 m a n vpp valid comparator n up to 85% efficiency n switching frequency: 500khz (typical) n quiescent current: 650 m a n low v cesat switch: 300mv at 0.5a (typical) n soft start reduces supply current transients n uses low value, small size, surface mount inductors n available in 8-lead so package u a o pp l ic at i ty p i ca l 12v, 60ma flash memory programming supply 12v output efficiency load current (ma) 1 70 efficiency (%) 72 74 76 78 86 10 100 LT1309 ?ta02 80 82 84 v in = 5v v in = 3.3v v in v sw l1* 10 m h d1 ? vpp 12v, 60ma sense vpp valid LT1309 on/off vpp valid r1 1m LT1309 ?ta01 c3 0.1 m f c2 1 m f** c1 4.7 m f murata erie lqh3c100k0ym00 ceramic motorola mbr0530 * ** ? on/off v in 3.3v to 5v soft start pgnd gnd + u s a o pp l ic at i n flash memory vpp generators n type ii and iii pcmcia card dc/dc converters n 3v to 12v, 5v to 12v converters n portable computers and instruments n cellular telephones n dc/dc converter module replacements , ltc and lt are registered trademarks of linear technology corporation. burst mode is a trademark of linear technology corporation. not recommended for new designs contact linear technology for potential replacement
2 lt13 0 9 a u g w a w u w a r b s o lu t exi t i s v cc voltage............................................................... 7v v sw voltage ............................................................ 20v v sense voltage ....................................................... 20v v on/off voltage......................................................... 7v v sel voltage ............................................................. 7v i lim voltage .............................................................. 7v maximum power dissipation ............................ 500mw operating temperature range ..................... 0 c to 70 c storage temperature range ................. C 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c wu u package / o rder i for atio order part number s8 part marking e lectr ic al c c hara terist ics t a = 25 c, v cc = 5v, v on/off = 3v, unless otherwise noted. symbol parameter conditions min typ max units i q quiescent current v sense = 12v 650 900 m a quiescent current, shutdown v on/off = 0.2v 9 15 m a input voltage range 2 6 v output sense voltage l 11.5 12 12.6 v output referred comparator hysteresis 35 mv f osc oscillator frequency current limit not asserted 400 500 700 khz dc maximum duty cycle l 80 85 92 % t on switch on time 1.7 m s reference line regulation 2v < v in < 6v 0.06 0.15 %/v v cesat switch saturation voltage i sw = 0.5a 230 350 mv switch leakage current v sw = 12v, switch off 0.1 10 m a switch current limit v in = 5v, soft start floating 400 600 900 ma v in = 3v, soft start floating 450 650 950 ma soft start current soft start grounded 80 120 m a on/off input voltage low 0.8 v on/off input voltage high 1.6 v on/off bias current v on/off = 5v 16.0 24.0 m a v on/off = 3v 8.0 14.0 m a v on/off = 0v 0.1 1.0 m a sense pin input current 50.0 90 m a v on/off = 0.2v 0.1 1 m a vpp valid threshold v sense rising (high to low transition) v sense C 200mv vpp valid output voltage low i sink = 100 m a 0.13 0.3 v vpp valid output voltage high i source = 2.5 m a 4 4.5 v LT1309cs8 1309 t jmax = 150 c, q ja = 150 c/w consult factory for industrial and military grade parts. the l denotes specifications which apply over the full operating temperature range. 1 2 3 4 8 7 6 5 top view on/off sense vpp valid gnd soft start v cc pgnd v sw s8 package 8-lead plastic so
3 lt13 0 9 typical perfor m a n ce characteristics u w temperature ( c) ?0 300 oscillator frequency (khz) 400 500 600 700 800 ?5 02550 1309 g01 75 100 oscillator frequency temperature ( c) ?0 100 switch saturation voltage (mv) 125 150 175 200 250 ?5 02550 1309 g03 75 100 225 i sw = 500ma temperature ( c) ?0 400 switch current (ma) 500 600 700 800 1000 ?5 02550 1309 g02 75 100 900 v cc = 3v v cc = 5v switch current limit supply current temperature ( c) ?0 300 supply current ( m a) 400 500 600 700 800 ?5 02550 1309 g05 75 100 v cc = 5v v cc = 3v sense voltage temperature ( c) ?0 sense voltage (v) 11.95 12.00 12.05 25 75 1309 g04 11.90 11.85 11.80 ?5 0 50 12.10 12.15 12.20 100 supply current in shutdown maximum duty cycle temperature ( c) ?0 70 maximum duty cycle (%) 75 80 85 90 95 ?5 02550 1309 g07 75 100 temperature ( c) ?0 8 10 12 25 75 1309 g06 6 4 ?5 0 50 100 2 0 supply current ( m a) 14 v cc = 5v v cc = 3v switch saturation voltage
4 lt13 0 9 typical perfor m a n ce characteristics u w 50 m s/div 1309 g08 12v v out 2v/div v on/off 10v/div vpp valid 10v/div start-up waveforms, i load = 10ma start-up waveforms, i load = 1ma 50 m s/div 1309 g09 v out 5v/div v on/off 10v/div i l 500ma/div 12v output 1v/div ac coupled 10ma 60ma i load 50 m s/div 1309 g10 pi fu ctio s uu u soft start (pin 1): a 0.1 m f/1m w parallel rc from this pin to gnd provides a soft start function upon device turn-on. initially about 80 m a will flow from the pin into the capacitor. when the voltage at the pin reaches approxi- mately 0.4v, current ceases flowing out of the pin. v cc (pin 2): input supply. at least 1 m f input bypass capacitance is required. more capacitance reduces ring- ing on the supply line. pgnd (pin 3) : power ground. connect to ground plane. v sw (pin 4): collector of power switch. high dv/dt present on this pin. to minimize radiated noise keep layout short and direct. gnd (pin 5): signal ground. connect to ground plane. vpp valid (pin 6): this pin provides a logic signal indicating that output voltage has reached 12v. active low with internal 200k pull-up resistor. sense (pin 7): output sense pin. this pin connects to a resistive divider that sets the output voltage. in shutdown, the resistor string is disconnected and current into this pin reduces to < 1 m a. on/off (pin 8): shutdown control. when pulled below 1.5v, this pin disables the LT1309 and reduces supply current to 9 m a. all circuitry is disabled in shutdown. the part is enabled when on/off is greater than 1.5v. load transient response, c out = 1 m f
5 lt13 0 9 operatio u the LT1309 is a current limited, burst mode (gated oscillator) type switching regulator that produces a 12v output from a 3.3v or 5v input. operation can best be understood by referring to the block diagram. when the voltage at the sense pin (pin 7) is less than 12v, compara- tor c1 enables the oscillator, turning switches q1 and q2 on. the switch turns off when current limit is reached or when the oscillator maximum on-time is reached. when q2 turns off, current built up in the inductor flows into the output capacitor and load. this action occurs until the output voltage reaches 12v. during start-up, the sense pin voltage is either 3.3v or 5v, depending on the input. the vpp valid signal remains high until the output voltage reaches 12v, signaling correct voltage level to program flash memory. connecting a 1 m f/0.1 m f parallel rc to the soft start pin limits inrush current during start-up. block diagra w v cc 8 on/off sense 7 4k 864k 200k vpp valid off q3 q2 1 q1 50 100k + c2 v ref 1.24v r1 3 w + c3 36mv v cc pgnd 1309 bd sw r2 700 w 5 3 4 gnd 1 soft start bias + 500khz oscillator + c1 2 power on 6
6 lt13 0 9 applicatio n s i n for m atio n wu u u inductor selection the low inductance value required with the LT1309 (10 m h) allows the use of very small units such as the murata-erie lqh3c100. requirements for the inductor include low dcr, ability to perform efficiently at 500khz and a satura- tion current rating of 700ma to 900ma. often inductor manufacturers rate maximum current for a small inductor based on self-heating considerations. for use in switching regulators where the inductor current is not constant the maximum specified dc current can be safely exceeded. capacitor selection the LT1309 needs very little input and output capacitance to function. output capacitance should be 1 m f or 2 m f for acceptable output ripple voltage. flash memory tolerates higher ripple voltage than might be suitable for a low noise system. the capacitor can be either a single high capaci- tance ceramic unit such as tokin 1e105zy5u-203 or murata-erie grm230y5v105z016, or can be distributed as 10 to 20 0.1 m f ceramic units. lower ripple can be obtained by increasing the capacitance to the 5 m f to 10 m f level. 2 m f to 5 m f of tantalum (low-q) capacitance is recommended on the input side to reduce resonance effects which can otherwise cause hundreds of millivolts of ripple voltage at the input. diode selection the LT1309s high switching speed demands a high speed rectifier. schottky diodes are preferred for their low for- ward drop and fast recovery. a suitable choice is the motorola mbr0520. this is a 0.5a, 20v schottky in a very small package that is 1.35mm high. pc board layout the component placement shown in figure 1 is recom- mended for pc board layouts. the high speed current paths are kept to a minimum distance and the switch node copper is minimized to keep radiated noise low. notice the placement of the input decoupling capacitor next to the ic. this is necessary for best performance. 1 2 3 4 8 7 6 5 on/off r1 v in v out c3 c2 gnd 1309 f01 c1 l1 d1 vpp valid figure 1. LT1309 recommended layout
7 lt13 0 9 package descriptio n u dimensions in inches (millimeters) unless otherwise noted. s8 package 8-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) 1 2 3 4 0.150 ?0.157** (3.810 ?3.988) 8 7 6 5 0.189 ?0.197* (4.801 ?5.004) 0.228 ?0.244 (5.791 ?6.197) 0.016 ?0.050 0.406 ?1.270 0.010 ?0.020 (0.254 ?0.508) 45 0 ?8 typ 0.008 ?0.010 (0.203 ?0.254) so8 0695 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) bsc dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * ** information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
8 lt13 0 9 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax : (408) 434-0507 l telex : 499-3977 ? linear technology corporation 1995 lt/gp 0896 7k ? printed in the usa related parts part number description comments lt1106 micropower step-up dc/dc converter, 12v at 60ma thin tssop package for type i pcmcia card lt1109-12 micropower step-up dc/dc converter, 12v at 60ma flash memory vpp generator, adjustable also lt1109a-12 micropower step-up dc/dc converter, 12v at 120ma vpp generator, adjustable also ltc ? 1262 inductorless flash memory programming supply, 12v at 30ma switched capacitor converter, no inductor lt1303 micropower high efficiency dc/dc converter with low-battery detector adjustable and fixed 5v, i out up to 200ma
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