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1 cat37 cmos white led driver boost converter ?2004 by catalyst semiconductor, inc. characteristics subject to change without notice doc no. 5005, rev. p typical application c1: taiyo yuden jmk212bj475 c2: taiyo yuden emk212bj105 d1: zetez zhcs400 l1: panasonic eljea6r8 or equivalent sot23 pin numbers figure 1. driver for four high-brightness white leds 2 3 1 5 4 sw vin shdn d1 vin 3 v to 5 v cat37 fb gnd off on 15ma features low quiescent ground current (0.5ma typical) power efficiency over 80% compatible pinout with lt1937 adjustable output current (up to 40ma) high frequency 1.2mhz operation input voltage operation down to 2.5v low resistance (0.5 ? ? ? ? ? ) power switch drives up to 4 white leds in series shutdown current less than 1 a load fault protection against open-circuits low value external components low profile 5-lead sot23 (1mm max) and tdfn (0.8mm) package description the cat37 is a dc/dc step up converter that delivers a regulated output current. operation at a constant switching frequency of 1.2mhz allows the device to be used with very small value external inductor and ceramic capacitors. the cat37 is targeted to drive multiple white light- emitting diodes (leds) connected in series and provides the necessary regulated current to control the brightness and the color purity. an external resistor r1 controls the output current level. led currents of up to 40ma can be supported over a wide range of input supply voltages from 2.5v to 7v, making the device ideal for battery- powered applications. applications color lcd and keypad backlighting cellular phones handheld terminals a high voltage output stage allows up to 4 white leds to be driven in series. series drive provides inherent current matching. led dimming can be done by using a dc voltage, a logic signal, or a pulse width modulation (pwm) signal. the shutdown input pin allows the device to be placed in power-down mode with ?ear zero?quiescent current. in addition to overcurrent limiting protection, the device also includes detection circuitry to ensure protection against open-circuit load fault conditions. the device is available in a low profile (1mm max height) 5-lead thin sot23 package and in a tdfn (0.8mm max height) package. digital cameras pdas/games portable mp3 players
cat37 2 doc. no. 5005, rev. p ordering information pin configuration pin descriptions pin number pin number sot23 tdfn name function 1 8 sw switch pin. this is the drain of the internal power switch. for minimum emi, minimize the trace area connected to this pin. 2 5 gnd ground pin. connect pin 2 to ground. 3 6 fb led (cathode) connection pin. 44 shdn shutdown pin. 5 2 vin input supply pin. this pin should be bypassed with a capacitor to ground. a 1 f capacitor mounted close to the pin is recommended. 1 power power ground ground (top view) tdfn package: 3mm x 3mm 0.8mm maximum height (rd4) (top view) tdfn package: 3mm x 4.9mm 0.8mm maximum height (rd2) r e b m u n t r a pe g a k c a p e b u t y t i t n a u q l e e r y t i t n a u q e g a k c a p e d o c g n i k r a m e r u t a r e p m e t e g n a r k k e 7 3 t a c) t h g i e h m m 1 ( 3 2 t o s , d a e l - 5f bc 5 8 o t c 0 4 - 7 e t - k k e 7 3 t a c ) t h g i e h m m 1 ( 3 2 t o s , d a e l - 5 l e e r & e p a t ? 0 0 3f bc 5 8 o t c 0 4 - 3 1 e t - 2 d r 7 3 t a c p o s m , m m 9 . 4 x 3 ( n f d t d a p - 8 ) t n i r p t o o f l e e r & e p a t 0 2 1d b tv e c cc 5 8 o t c 0 4 - 3 1 e t - 4 d r 7 3 t a c ) m m 3 x 3 ( n f d t d a p - 8 l e e r & e p a t 0 2 1d b tw e c cc 5 8 o t c 0 4 - cat37 1 2 3 5 4 sw gnd fb vin shd n 5-lead sot-23 1mm maximum height [free air] 1 2 3 4 8 7 6 5 sw nc fb gnd power gnd vin nc shdn 1 2 3 4 8 7 6 5 sw nc fb gnd power gnd vin nc shdn
cat37 3 doc no. 5005, rev. p absolute maximum ratings v in , fb, shdn voltage ......................................... 8 v sw voltage .......................................................... 20 v junction temperature ....................................... 125 c electrical specifications over recommended operating conditions unless otherwise specified. t a = 25 ? c, v in = 3v and v shdn = 3v. storage temperature .......................... -65 c to 160 c esd rating - human body model .................... 2000v lead soldering temperature ............................ 300 c symbol parameter conditions min typ max units input voltage range 2.5 7 v i q quiescent current v fb = 0.2 v 0.5 0.7 ma i sd shutdown current v shdn = 0 v 0.05 1 a v fb fb pin voltage 4 leds at 15 ma 85 95 105 mv i fb fb pin leakage current 1 2 a shutdown high threshold 0.85 v shutdown low threshold 0.25 v i shdn shutdown pin current 1 na f sw boost converter frequency 0.8 1.2 1.6 mhz dc maximum switch 90 95 % duty cycle i swl switch current limit 400 550 780 ma switch saturation voltage i sw = 300 ma 150 200 mv switch leakage current switch off, v sw = 5 v 0.01 5 a efficiency figure 1 with 83 % specified components recommended operating conditions r e t e m a r a pe g n a rt i n u v n i 7 o t 5 . 2v e g n a r e r u t a r e p m e t t n e i b m a5 8 + o t 0 4 - c 1 l r o t c u d n il a c i p y t % 0 2 8 . 6h 1 c r o t i c a p a c t u p n il a c i p y t % 0 2 0 . 1f 2 c r o t i c a p a c t u p t u ol a c i p y t % 0 2 0 . 1f i d e l s e i r e s n i s d e l 4 o t 1 h t i w0 2 o t 0a m
cat37 4 doc. no. 5005, rev. p typical characteristics v in = 3.6 v,t amb = 25 ? c, c in = 4.7 f, c out = 1 f, l = 6.8 h, unless otherwise specified. 14.0 14.5 15.0 15.5 16.0 -50 -25 0 25 50 75 100 4 leds 4 leds led current [ma] led current vs. temperature 80 85 90 95 100 105 110 0 5 10 15 20 led current [ma] 3 leds fb pin voltage [mv] 3 leds fb pin voltage vs. led current 0.8 0.9 1.0 1.1 1.2 1.3 -50 -25 0 25 50 75 100 load =20 ma load = 3 leds vin = 3.6v switching frequency [mhz] load = 20ma load = 3 leds vin = 3.6v switching frequency vs. temperature 0 10 20 30 23 4 56 input voltage [v] 3 leds 20ma 1 0 ma led current [ma] 3 leds 20ma 10ma led current vs. input voltage 0.8 0.9 1.0 1.1 1.2 1.3 12 34 5 6 input voltage [v] 4 leds switch frequency [mhz] switching frequency vs. input voltage 80 85 90 95 100 -50 -25 0 25 50 75 100 4 leds at 15ma vin = 3.6v fb pin voltage [mv] 4leds at 15ma vin = 3.6v fb pin voltage vs. temperature 4 leds
cat37 5 doc no. 5005, rev. p 60 65 70 75 80 85 90 23 456 input voltage [v] 3 leds at 15ma vout = 10v 3 leds at 15ma vout = 10v efficiency vs. input voltage efficiency [%] 74 76 78 80 82 84 86 -50 -25 0 25 50 75 100 temperature [oc] load =3 leds vin = 3.6v load =20 ma load =15 ma load =10 ma load = 3 leds vin = 3.6v load = 20 ma load = 15 ma load = 10 ma efficiency vs. temperature efficiency [%] v sw , i l , & v out waveforms pwm on shdn shdn shdn shdn shdn pin at 1khz enable power-up waveforms typical characteristics v in = 3.6 v,t amb = 25 ? c, c in = 4.7 f, c out = 1 f, l = 6.8 h, unless otherwise specified.
cat37 6 doc. no. 5005, rev. p operation the cat37 device is a high efficiency, constant frequency, current regulating boost driver for white leds. the device includes a switch and an internally compensated loop for the regulation of the current in the leds. operation can be best understood by examining the block diagram. the fb pin is regulated at 95 mv and the current through the external resistor will set the regulated current in the leds at: i led = 0.095/r1 while maintaining led current regulation, the cat37 boost converter automatically adjusts the fb pin voltage to be as low as possible. a low fb pin voltage ensures high efficiency. current through the internal power switch is continuously monitored cycle-by-cycle. if the current limit is exceeded, the switch is immediately turned off, protecting the device, for the remainder of the cycle. pwm dimming operation can be achieved by switching the shdn pin or by pulling the fb pin higher than 95mv. block diagram figure 2. cat37 block diagram vin 1.2 mhz clock pwm & logic + - d1 l1 vin c1 2 fb current sense amp sw 1 5 cat37 3 error amp c2 4 shdn gnd 0.095v ref i led r1 + - over voltage protection (22v) note: sot23 pin numbers
cat37 7 doc no. 5005, rev. p diode selection schottky diodes, with their low forward voltage drop and fast switching speed, are the ideal choice for high efficiency applications. table 2 shows several different schottky diodes that work well with the cat37. make sure that the diode has a voltage rating greater than the output voltage. the diode conducts current only when the power switch is turned off (typically less than one- third the time), so a 0.4a or 0.5a diode will be sufficient for most designs. led current programming the led current is programmed with a single resistor connected to the fb pin. the fb pin is internally regulated to 95 mv, which sets the current flowing through r1 and the leds as equal to 0.095/r1. for the best accuracy, a 1% or better resistor is recommended. table 3 shows several typical 1% r1 values. for other led current values, use the following equa- tion to choose r1. r1= 0.095 i led most white leds are driven at maximum currents of 15ma to 20ma. some higher power designs will use two parallel strings of leds for greater light output, resulting in 30ma to 40ma (two strings of 15ma to 20ma) flowing through the r1 resistor. application information capacitor selection low esr (equivalent series resistance) capacitors should be used at the output to minimize the output ripple voltage. the low esr and small package options available with multilayer ceramic capacitors make them excellent choices. the x5r and x7r capacitor types are preferred because they retain their capacitance over wider voltage and temperature ranges than the y5v or z5u types. a 1.0 f output capacitor is recommended for most applications. the voltage rating of the output capacitor c2 depends on the number of leds driven in the series. a 16 v ceramic capacitor is recommended when driving 3 or 4 leds. low profile ceramic capacitors with a 1mm maximum height/thickness are available for designs height requirements. ceramic capacitors also make a good choice for the input capacitor, which should be mounted as close as possible to the cat37. a 1 f or 4.7 f input capacitor is recommended. table 1 shows a list of several ceramic capacitor manufacturers. consult the manufacturers for detailed information as new products and package options are introduced regularly. table 1. ceramic capacitor manufacturers supplier web taiyo yuden www.t-yuden.com murata www.murata.com kemet www.kemet.com avx www.avxcorp.com table 3. r1 resistor values i led (ma) r1 ( ? ) 40 2.37 30 3.16 20 4.75 15 6.34 12 7.87 10 9.53 5 19.1 table 2. schottky diode suppliers part supplier mbr0520 on semiconductor mbr0530 www.onsemi.com mbr0540 800.282.9855 zhcs400 zetex
cat37 8 doc. no. 5005, rev. p pcb layout guidelines the cat37 is a high-frequency switching regulator where proper pcb board layout and component placement can minimize noise and radiation and increase efficiency. to maximize efficiency, the cat37 design has fast switch rise and fall times. to prevent radiation and high frequency resonance problems minimize the length and area of all traces connected to the sw pin and use a ground plane under the switching regulator. the sw pin, schottky diode and capacitor c2 signal path should be kept as short as possible. the ground connection for the r1 resistor should be tied directly to the gnd pin and not be shared with other components. led dimming with dc signal dimming the leds can be done by applying a variable dc voltage as shown on figure 3. as the v dc increase the voltage across r1 decreases and therefore lower the led current. the resistors r2 and r3 must be large enough so that their current (tens of a) is much smaller than the led current but much larger than the fb leakage current (i fb ). when adjusting v dc between 0v and 2v, the resistors shown on figure 3 will set the led current between 0ma and 15ma. led dimming with pwm signal pwm brightness control provides the widest dimming range (greater than 20:1). by turning the leds on and off using the control signal, the leds operate at either zero or full current, but their average current changes with the pwm signal duty cycle. typically, a 5khz to 40khz pwm signal is used. a filtered pwm signal is used to dim the leds, as shown in figure 4. in addition to providing the widest dimming range, pwm brightness control also ensures the purest white led color over the entire dimming range. the true color of a white led changes with operating current, and is the purest white at a specific forward current, usually 15ma or 20ma. if the led current is less than or more than this value, the emitted light becomes more blue. applications involving color lcds can find the blue tint objectionable. figure 3. dimming with a dc voltage cat37 fb r 1 r incr logic signal 2n7002 cat37 fb r 3 18k pwm 10k r 2 1k cat37 fb r 3 18k v dc r 2 1k figure 4. dimming with a filtered pwm signal figure 5. dimming with a logic signal led dimming with a logic signal for applications that need to adjust the led brightness in discrete steps, a logic signal can be used as shown in figure 5. r 1 sets the minimum led current value (when the nmos switch is off): r1= 0.095v i led(min) r incr determines how much led current increases when the external nmos switch is turned on. r incr = 0.095v i led(increase)
cat37 9 doc no. 5005, rev. p typical application circuits the application diagrams are shown for the sot23 pin numbers. three leds with dc level dimming control four leds with pwm dimming control efficiency - three leds 60 65 70 75 80 85 90 0 5 10 15 20 25 30 led current [ma] vin=3.0v vin=3.6v efficiency [%] vin = 3.6v vin = 3.0v efficiency - four leds 60 65 70 75 80 85 90 0 5 10 15 20 25 30 led current [ma] vin = 3.0v vin = 3.6v vin = 3.0v vin = 3.6v efficiency [%] efficiency - two leds two leds with dc level dimming control 60 65 70 75 80 85 90 0 5 10 15 20 25 led current [ma] vin=3.0v vin=3.6v efficiency [%] vin = 3.6v vin = 3.0v 30 15ma 2 3 1 5 4 sw vin shdn d1 vin 3 v to 4.2 v cat37 fb gnd v dc dimming 1k 18k 15ma 2 3 1 5 4 sw vin shdn d1 vin 3 v to 4.2 v cat37 fb gnd v dc dimming 1k 18k 15ma 2 3 1 5 4 sw vin shdn d1 vin 3 v to 4.2 v cat37 fb gnd pwm 1k 18k 10k
cat37 10 doc. no. 5005, rev. p package outlines 5-lead sot-23 all dimensions in millimeters 0.50 max 0.35 min 3.00 max 2.60 min 0.15 max 0.00 min 1.00 max 3.00 max 2.80 min 0.90 max 0.80 min 1.75 max 1.50 min 0.20 max 0.09 min 0.60 max 0.10 min 0.20 gauge plane 0.95 ref 1.90 ref 0.70 max 0.50 min pin 1
cat37 11 doc no. 5005, rev. p tdfn 3x3 mm package (rd4) 3.00 + 0.10 (s) 85 1 4 3.00 + 0.10 (s) pin 1 index area c 0.75 + 0.05 0.0 - 0.05 0.30 + 0.07 (8x) 0.25 min. 0.75 + 0.05 a b 58 2.30 + 0.10 c0.35 pin 1 id 1.50 + 0.10 1.95 ref. (2x) 0.65 typ. (6x) 0.30 + 0.10 (8x) 1 2x 2x 0.15 0.15 c c note: 1. all dimension are in mm. angles in degrees. 2. coplanarity shall not exceed 0.08 mm. 3. warpage shall not exceed 0.10 mm. 4. package length / package width are considered as special characteristic(s) 5. refer jedec mo-229 / weec
cat37 12 doc. no. 5005, rev. p tdfn 3x4.9 mm package (rd2) d 0.08 c f 0.10 c 0.10m c a b 0.15 8 5 a 5 b 8 3.00 + 0.15 2.00 + 0.15 0.10 0.15 0.20 0.25 pin 1 id 0.60 + 0.10 (8x) d 0.15 c 2x 4.90 + 0.10 (5) 1 pin 1 index area 3.00 + 0.10 (s) 4 2x d c 4 0.30 + 0.05 (8x) 8x j 1.95 ref. (2x) 1 0.65 typ. (6x) 0.75 + 0.05 0.0-0.05 8x 0.20 ref. c note: 1. all dimension are in mm. angles in degrees. 2. coplanarity applies to the exposed pad as well as the terminals. coplanarity shall not exceed 0.08mm. 3. warpage shall not exceed 0.10mm. 4. package length / package width are considered as special characteristic(s). 5. refer to jedec mo-229, footprints are compatible to 8 msop.
cat37 14 doc. no. 5005, rev. p catalyst semiconductor, inc. corporate headquarters 1250 borregas avenue sunnyvale, ca 94089 phone: 408.542.1000 fax: 408.542.1200 www.catalyst-semiconductor.com publication #: 5005 revison: p issue date: 6/15/04 copyrights, trademarks and patents trademarks and registered trademarks of catalyst semiconductor include each of the following: dpp ae 2 catalyst semiconductor has been issued u.s. and foreign patents and has patent applications pending that protect its products. for a complete list of patents issued to catalyst semiconductor contact the companys corporate office at 408.542.1000. catalyst semiconductor makes no warranty, representation or guarantee, express or implied, regarding the suitability of its products for any particular purpose, nor that the use of its products will not infringe its intellectual property rights or the rights of third parties with respect to any particular use or application and specifically disclaims any and all liability aris ing out of any such use or application, including but not limited to, consequential or incidental damages. catalyst semiconductor products are not designed, intended, or authorized for use as components in systems intended for surgica l implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the catalyst semic onductor product could create a situation where personal injury or death may occur. catalyst semiconductor reserves the right to make changes to or discontinue any product or service described herein without not ice. products with data sheets labeled "advance information" or "preliminary" and other products described herein may not be in production or offered for sale . catalyst semiconductor advises customers to obtain the current version of the relevant product information before placing order s. circuit diagrams illustrate typical semiconductor applications and may not be complete.

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