View CAT4237TS_2766622.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

cat4237 ? 2005 catalyst semiconductor, inc. 1 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice high voltage cmos boost white led driver features drives 6 to 8 white leds in series from 3v up to 87% efficiency low quiescent ground current 0.6 ma adjustable output current (up to 40ma) high frequency 1mhz operation high voltage power switch shutdown current less than 1 m a open led low power mode automatic shutdown at 1.9v (uvlo) thermal shutdown protection thin sot23 5 - lead (1mm max height) applications color lcd and keypad backlighting cellular phones handheld devices digital cameras pdas portable game machine orderin g information part number package quantity per reel package marking CAT4237TS t sot 23 - 5 3000 ls cat4237td t sot23 - 5 lead free 1 3000 lt note 1: nipdau lead plating product description the cat4237 is a dc/dc step - up converter that delivers an accurate constant current ideal f or driving leds. operation at a constant switching frequency of 1mhz allows the device to be used with small value external ceramic capacitors and inductor. leds connected in series are driven with a regulated current set by the external resistor r1. led c urrents up to 40ma can be supported over a wide range of input supply voltages from 2.8v to 5.5v, making the device ideal for battery - powered applications. the cat4237 high - voltage output stage is perfect for driving six, seven or eight white leds in seri es with inherent current matching in lcd backlight applications . 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 ?zero? quiescent current . in addition to thermal protection and overload current limiting , th e device also enters a very low power operating mode during ?open l ed ? fault conditions. the device is ho u sed in a low profile (1mm max height) 5 - lead thin sot23 packag e for space critical applications. p in c onfiguration top view 5 - lead thin sot23 1mm max height typical application circuit l: sumida cdrh3d16 - 330 d: central cmdsh05 - 4 (rated 40v) c2: taiyo yuden umk2 12bj224 (rated 50v)
cat4237 ? 2005 catalyst semiconductor, inc. 2 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice absolute maximum rat ings parameter rating unit v in , fb voltage - 0.3 to +7 v shdn* voltage - 0.3 to +7 v sw voltage - 0.3 to 60 v storage temperature range - 65 to +1 6 0 c junction temperature r ange - 40 to +125 c lead temperature 300 c recommended operating conditions typical application circuit with external components are shown on page 1. parameter range unit v in 2. 8 to 5 .5 v sw pin voltage 0 to 30 v ambient temperature r ange - 40 to +85 c 6, 7 or 8 leds 1 to 4 0 ma el ectrical operating c haracteristics vin = 3 .6 v , ambient temperature of 25oc (over recommended operating conditions unless specified otherwise) symbol parameter conditions min t yp m ax u nit i q operating current v fb = 0. 2 v v fb = 0. 4 v (not switching) 0. 6 0.1 1.5 0. 6 ma i sd shutdown current v shdn* = 0v 0. 1 1 a v fb fb pin voltage 8 leds with i led = 20 ma 2 8 5 3 0 0 3 15 m v i fb fb pin input leakage 1 a i led programmed led current r 1 = 10 w r 1 = 15 w r 1 = 20 w 2 8 .5 1 9 1 4 .25 30 20 15 3 1.5 21 1 5.75 ma v ih v il shdn* l ogic high shdn* logic low enable threshold level shutdown threshold level 0.4 0.8 0.7 1.5 v v f sw switching frequency 0.8 1 .0 1. 3 mhz i lim switch current limit 35 0 45 0 60 0 ma r sw switch ?on? resistance i sw = 100ma 1 .0 2 .0 w i leak switch le akage current switch off, v sw = 5v 1 5 a thermal shutdown 150 oc thermal hysteresis 20 oc v uvlo undervoltage l ockout (uvlo) t hreshold 1.9 v v ov - sw overvoltage threshold 35 v
cat4237 ? 2005 catalyst semiconductor, inc. 3 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice pin description v in is the supply input for the internal l ogic the device is compatible with supply voltage s down to 2.8v and up to 5. 5v. it is recommended that a small bypass ceramic capacitor ( 4.7 uf) be placed between the v in and gnd pins near the device. if the supply voltage drops below 1. 9v, the device stops switching. shdn* is the shutdown logic input . when the pin is ti ed to a voltage low er than 0.4v , the device is in shutdown mode , draw ing nearly zero current. when the pin is connected to a voltage high er than 1.5v , the device is enabled. gnd is the grou nd reference pin. this pin should be connected directly to the ground place on the pcb. sw pin is connected to the drain of the internal cmos power switch of the boost converter. the inductor and the schottky diode anode should be connected to the sw pin. traces going to the sw pin should be as short as possible with minimum loop area. an over - voltage detection circuit is connected to the sw pin. when the voltage reaches 35v, the device enters a low power operating mode preventing the sw voltage from exceed ing the maximum rating. fb feedback pin is regulated at 0.3v. a resistor connected between the fb pin and ground sets the led current according to the formula : i led = 0.3v/r1 the lower led cathode is connected to th e fb pin. pin # name function 1 sw switch pin. this is the drain of the internal power switch. 2 gnd ground pin. connect the pin to the ground plane. 3 fb feedback pin. connect to the last led cathode. 4 sh dn* shutdown pin (logic low) . set high to enable the driver. 5 vin power suppl y input . block diagram
cat4237 ? 2005 catalyst semiconductor, inc. 4 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice device operation the cat4237 is a fixed frequency (1mhz), low noise, inductive boost converter that provid es a constant current with excellent line and load regulation . the device uses a high - voltage cmos power switch between the sw pin and ground to energize the inductor . when the switch is turned off, the stored energy in the inductor is released into the load via the schottky diode. the on/off duty cycle of the power switch is internally adjusted and controlled to maintain a constant regulated voltage of 0.3v across the feedback resistor connected to the feedback pin (fb). the value of the resistor sets the led current accordingly ( 0.3v/r1 ) . during the initial power - up stage, the duty cycle of the internal power switch is l imited to prevent excessive in - rush currents and thereby provide a ?soft - start? mode of operation. while in normal operation, t he device can deliver up to 4 0ma of load current into a string of up to 8 white leds. in the event of a ?open l ed ? fault condi tion, where the feedback control loop becomes open, the output voltage will continue to increase. once this voltage exceeds 35v, an internal protection circuit will become active and place the device into a very low power safe operating mode where only a s mall amount of power i s transferred to the output. this is achieved by pulsing the switch once every 60 m s and keep it on for about 1 m s only . thermal overload protection circuitry has been included to prevent the device from operating at unsafe junction temperatures above 150 oc . in the event of a thermal overload condition the device will automatically shutdown and wait till the junction temperatures cools to 130 oc before normal operation is resumed. light load operation under light load condition (u nder 4ma) and with input voltage above 4.2v, the cat4237 driving 6 leds , the driver start s pulse skipping . although the led current remains well regulated , some lower frequency ripple may appear. switching waveform vin = 4.2v , i led = 4ma
cat4237 ? 2005 catalyst semiconductor, inc. 5 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice typical char acteristics v in = 3.6v, c in = 4.7uf, c out = 0.22f, l = 33h with 8 l eds at 20ma, t amb =25oc, unless otherwise specified. quiescent current vs . vin (not switching) 0 20 40 60 80 100 120 140 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 input voltage [v] input current [ua] vfb =0.4v (not switching) quiescent current vs . vin ( s witching) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 input voltage [v] supply current [ma] f b pin voltage vs . supply voltage 285 290 295 300 305 310 315 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 input voltage [v] feedback [mv] 8leds at 20ma vout= 26v fb pin vo ltage vs . output current 285 290 295 300 305 310 315 0 5 10 15 20 25 30 output current [ma] fb pin voltage [mv] 8 leds switching frequency vs . supply voltage 960 980 1000 1020 1040 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 input voltage [v] frequency [khz] switching wave form s
cat4237 ? 2005 catalyst semiconductor, inc. 6 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice typical characteristics v in = 3.6v, c in = 4.7uf, c out = 0.22f, l = 33h, with 8 l ed s at 20ma, t amb =25oc, unless otherwise specified. led current vs . input volta ge (8 leds) 0 5 10 15 20 25 30 35 2.5 3.0 3.5 4.0 4.5 5.0 input voltage [v] led current [ma] r fb = 10 w r fb = 15 w r fb = 20 w led current regulation (20ma) -1.0% -0.5% 0.0% 0.5% 1.0% 3.0 3.3 3.6 3.9 4.2 4.5 4.8 input voltage [v] current variation [%] . 8 led efficiency vs. load current 65 70 75 80 85 90 5 10 15 20 25 30 led current [ma] efficiency [%] vin = 3.6v vin = 4.2v 8 leds vout ~ 27v at 20ma l = 33uh 8 led efficiency vs. input voltage 65 70 75 80 85 90 3.0 3.5 4.0 4.5 5.0 input voltage [v] efficiency [%] 15ma 20ma 8 leds vout ~ 27v at 20ma l = 33uh 7 led efficiency vs. load current 65 70 75 80 85 90 5 10 15 20 25 30 led current [ma] efficiency [%] vin = 3.6v vin = 4.2v 7 leds vout ~ 23v at 20ma l = 33uh 6 led efficiency vs. load current 65 70 75 80 85 90 5 10 15 20 25 30 led current [ma] efficiency [%] vin = 3.6v vin = 4.2v 6 leds vout ~ 20v at 20ma l = 33uh
cat4237 ? 2005 catalyst semiconductor, inc. 7 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice typical characteristics v in = 3.6v, c in = 4.7uf, c out = 0 .22f, l = 33h, with 8 leds at 20ma, t amb =25oc, unless otherwise specified. power - up with 8 leds at 20ma switch on resistance vs. input voltage 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 input voltage [v] switch resistance [ohm] fb pin voltage vs. temperature 297 298 299 300 301 302 303 -50 0 50 100 150 temperature [oc] feedback voltage [mv] v in =3.6v, 8leds i led =20ma shutdown voltage vs. input voltage 0.2 0.4 0.6 0.8 1.0 3.0 3.5 4.0 4.5 5.0 input voltage [v] shutdown voltage [v] 125 c 25c 85c -40c maximum output current vs. input voltage 0 20 40 60 80 100 120 140 2.5 3.0 3.5 4.0 4.5 5.0 input voltage [v] max output current [ma]. vout = 15v vout = 20v
cat4237 ? 2005 catalyst semiconductor, inc. 8 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice application informat ion external component selection capacitors the cat4 2 37 only requires small ceramic capacitors of 4.7uf on the input and 0.22 f on the output . under normal condition, a 4.7 f input capacitor is sufficient. for applicat ions with higher output power, a larger input capacitor of 10 f may be appropriate. x5r and x7r capacitor types are ideal due to their stability across temperature range. inductor a 33 h inductor is recommended for most of the cat4237 applications. in ca ses where the efficiency is critical, inductances with lower series resistance are preferred. inductors with current rating of 300ma or higher are recommended for most applications. sumida cdrh3d16 - 330 33 h inductor has a rated current of 320ma and a serie s resistance (d.c.r.) of 520m w typical. schottky d iode the current rating of the schottky diode must exceed the peak current flowing through it. the schottky diode performance is rated in terms of its forward voltage at a given current. in order to achie ve the best efficiency, this forward voltage should be as low as possible. the response time is also critical since the driver is operating at 1mhz. central semiconductor schottky diode cmdsh05 - 4 ( 5 00ma rated) is recommended for most applications. led cur rent setting the led current is set by the external resistor r1 connected between the feedback pin (fb) and ground. the formula below gives the relationship between the resistor and the current: r1 = 0.3v/led current led current (ma) r1 ( w ) 5 60 10 30 15 20 20 15 25 12 30 10 table 1. resistor r1 and led current
cat4237 ? 2005 catalyst semiconductor, inc. 9 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice open led protection in the event of an ?open led? fault condition, the cat4 2 37 will continue to boost the output voltage with maximum power until the output voltage reaches approximate ly 35v . once the output exceeds this level, the internal circuitry immediately place s the device into a very low power mode where the total input power is limited to about 4mw (about 1ma input current with a 3.6v supply). the sw pin clamp s at a voltage bel ow its maximum rating of 60v. there is no need to use an external zener diode between vout and the fb pin. a 50v rated c2 capacitor is required to prevent any overvoltage damage in the open led condition. open led p rotection with out zener open led switching waveforms with out zener open led supply current vs. vin with out zener 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 input voltage [v] supply current [ma] open led ou t put voltage vs . vin with out zener 30 35 40 45 50 2.5 3.0 3.5 4.0 4.5 5.0 input voltage [v] output voltage [v]
cat 4237 ? 2005 catalyst semiconductor, inc. 10 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice dimming control there are several methods available to control the led brightness. pwm signal on the shdn* pin led brightness dimming can be done by applying a pwm signal to the shdn* input. the led current is repetitively turned on and off, so that the average current is proportional to the duty cycle. a 100% duty cycle, with shdn* always high, corresponds to the led s at nominal current. figure 1 shows a 1khz signal with a 50% duty cycle applied to the shdn* pin. t he recommended pwm frequency range is from 100hz to 2khz. figure 1. switching waveform with 1khz pwm on shdn* filtered pwm signal a filtered pwm signa l u sed as a variable dc voltage can control the led current . f igure 2 s hows the pwm control circuitry connected to the cat4237 fb pin. the pwm signal has a voltage swing of 0v to 2.5v. the led current can be dimmed within a range from 0 to 20ma. the pwm si gnal frequency can vary from very low frequency up to 100khz. figure 2 . circuit for filtered pwm signal a pwm signal at 0v dc, or a 0% duty cycle, results in a max led current of about 22ma. a pwm signal with a 93% duty cycle or more, results in an led current of 0ma.
cat 4237 ? 2005 catalyst semiconductor, inc. 11 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice board layout the cat4237 is a high - frequency switching regulator. the traces that carr y the high - frequency switching current have to be carefully layout on t he board in order to minimize emi, ripple and noise in general. the thicker lines on figure 3 show the switching current path. all these traces have to be short and wide enough to minimize the parasitic inductance and resistance. the loop shown on figure 3 corresponds to the current path when the cat4237 internal switch is closed. on figure 4 is shown the current loop, when the cat4237 switch is open. both loop areas should be as small as possible. capacitor c1 has to be placed as close as possible to the vin pin and gnd. the c apacitor c2 has to be connected separately to the top led anode. a ground plane under the cat4237 allows for direct connection of the capacitor s to ground . the r esistor r1 must be connected directly to the gnd pin of the cat4237 and n ot shared with the switching current loops and any other components. figure 3 . closed - switch current loop closed figure 4 . open - switch current loop open
cat 4237 ? 2005 catalyst semiconductor, inc. 12 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice package outlines 5 - lead sot - 23 all dimensions in millimeters
cat 4237 ? 2005 catalyst semiconductor, inc. 13 of 13 doc. no . 5013, rev. a characteristics s ubject to change without notice revision history date revision rea son 10 / 1 4 /2005 a initial issue copyrights, trademarks and patents trademarks and registered trademarks of catalyst semiconductor include each of the following: dpp ? ae2 ? 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 company?s corporate office at 408.542.1 000. 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 th e rights of third parties with respect to any particular use or application and specifically disclaims any and all liability arising out of any such use or application, including but not limited to, consequential or incidental damages. catalyst semiconduc tor products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the catalys t semiconductor 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 notice. products with data sheets labele d "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 orders. ci rcuit diagrams illustrate typical semiconductor applications and may not be complete. catalyst semiconductor, inc. corporate headquarters 1250 borregas avenue sunnyvale, ca 94089 phone: 408.542.1000 fax: 408.542.1200 www.catalyst - semiconductor.com publication #: 5013 revision: rev. a issue date: 10 / 14 /05

▲Up To Search▲

Price & Availability of CAT4237TS

	To Download CAT4237TS Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .