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pam2861 document number: dsxxxxx rev. 1 - 1 1 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated 1a led driver with internal switch description the pam2861 is a continuous mode i nductive step-down converter, designed for driving single or mu ltiple series connected leds efficiently from a voltage source higher than the led voltage. the device operates from an input supply between 6v and 40v and provides an externally adjustabl e output current of up to 1a. depending upon supply voltage and external components, this can provide up to 30 watts of output power. the pam2861 includes the output switch and a high-side output current sensing circuit, which uses an external resistor to set the nominal average output current. output current can be adjusted below the set value, by applying an external control signal to the vset pin. the vset pin will accept either a dc voltage or a pwm waveform. the soft-start time can be increased using an external capacitor from the vset pin to ground. applying a voltage of 0.2v or lower to the vset pin turns the output off and switches the device into a low current standby state. features ? simple low parts count ? internal 40v ndmos switch ? 1a output current ? single pin on/off and brightness control using dc voltage or pwm ? soft-start ? high efficiency (up to 97%) ? wide input voltage range: 6v to 40v ? output shutdown ? open led protection ? short led protection ? up to 1mhz switching frequency ? inherent open-circuit led protection ? typical 5% output current accuracy ? pb-free tsot25 and sot89-5 packages pin assignments applications ? low voltage halogen replacement leds ? low voltage industrial lighting ? led back-side lighting ? illuminated signs top view tsot25
pam2861 document number: dsxxxxx rev. 1 - 1 2 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated typical applications circuit pin descriptions pin number pin name function 1 lx drain of ndmos switch. 2 gnd ground (0v) 3 vset ? multi-function on/off and brightness control pin: ? leave floating for normal operation. ? drive to voltage below 0.2v to turn off output current ? drive with dc voltage (0.3v < vset< 2.5v) to adjust output current from 12% to 100% of i out nom ? drive with pwm signal from open-colle ctor or open-drain transistor, to adjust output current. adjustment range 1% to 100% of i out nom for f < 500hz ? connect a capacitor from this pin to ground to increase soft-start time. (default soft-start time = 0.1ms. addi tional soft-start time is approx.1.5ms/1nf) 4 isense connect resistor rs from this pin to vi n to define nominal average output current i out nom = 0.1/rs 5 vin input voltage (6v to 40v). decouple to ground with 10 f or higher x7r ceramic c apacitor close to device.
pam2861 document number: dsxxxxx rev. 1 - 1 3 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated functional block diagram absolute maximum ratings (@t a = +25c, unless otherwise specified.) these are stress ratings only and functional operation is not implied. exposure to absolute maximum ratings for prolonged time periods may affect device reliability. all voltages are with respect to ground. parameter rating unit input voltage range -0.3 to +40 v lx, i sense pin voltage -0.3 to +40 vset pin voltage -0.3 to +6.0 maximum junction temperature 170 c storage temperature -65 to +170 soldering temperature 300, 5sec recommended operating conditions (@t a = +25c, unless otherwise specified.) parameter rating unit input voltage range 6 to 40 v ambient temperature range -40 to +85 c junction temperature range -40 to +150
pam2861 document number: dsxxxxx rev. 1 - 1 4 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated thermal information parameter package symbol max unit thermal resistance (junction to ambient) tsot25 ja 250 c/w sot89-5 160 thermal resistance (junction to case) tsot25 jc 130 sot89-5 45 electrical characteristics (@t a = +25c, v in = 16v, unless otherwise specified.) parameter symbol test conditions min typ max units input voltage v in 6 40 v output current i led r s = 0.3 ? 333 ma r s = 0.1 ? 1 a shutdown current i sd vset pin grouded 20 40 a quiescent current without switching i q vset pin floating, v in = 16v 0.6 ma mean current sense threshold voltage v sense measured on i sense pin with respect to v in 95 100 105 mv sense threshold hysteresis v sense_hys 13 % isense pin input current i sense v sense = v in -0.1 8 a vset range on vset pin v en for dc dimming 0.3 2.5 v dc voltage on vset pin to enable v en(on) v en rising 0.25 v dc voltage on vset pin to disable v en(off) v en falling 0.2 v lx switch on resistance r lx @i lx = 100ma 0.3 ? lx switch leakage current i lx(leak) 5 a soft start time t ss v in = 16v, c en = 1nf 1.5 ms operating frequency f lx v i = 16v, v o = 9.6v (3 leds) l = 47f, i = 0.25a (i led = 1a) 233 khz recommended minimum switch on time t on_rec for 4% accuracy 500 ns recommended maximum switch frequency f lx(max) 1.0 mhz max duty circle 98 % recommended duty cycle range d lx 25 75 % internal comparator propagation delay t pd (note 1) 45 ns over temperature protection t otp 150 c temp protection hysteresis t otp_hys 40 c current limit i xl(max) peak inductor current 1.5 a note: 1. parameters are not tested at production, but guaranteed by design. v sense : level a: 95mv to 100mv; level b: 100mv to 105mv.
pam2861 document number: dsxxxxx rev. 1 - 1 5 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated typical performance characteristics (@t a = +25c, v in = 16v, unless otherwise specified.)
pam2861 document number: dsxxxxx rev. 1 - 1 6 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated typical performance characteristics (cont.) (@t a = +25c, v in = 16v, unless otherwise specified.)
pam2861 document number: dsxxxxx rev. 1 - 1 7 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated typical performance characteristics (cont.) (@t a = +25c, c in = 10f, c o = 10f, l = 4.7h, unless otherwise specified.)
pam2861 document number: dsxxxxx rev. 1 - 1 8 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated application information setting nominal average output current with external resistor r s the nominal average output current in the led(s) is determined by the value of the external current sense resistor (r s ) connected between vin and i sense and is given by: r 1.0 i s )nom(out ? the table below gives values of nominal average output current for several preferred values of current setting resistor (r s ) in the typical application circuit shown on page 1. r s ( ? ) nominal average output current (ma) 0.1 1000 0.13 760 0.15 667 0.3 333 the above values assume that the vset pin is floating and at a nominal voltage of vref (1.25v). note that r s = 0.1 is the minimum allowed value of sense resistor under thes e conditions to maintain switch current below the specified maximum value. it is possible to use different values of r s if the vset pin is driven from an external voltage. capacitor selection a low esr capacitor should be used for input decoupling, as the esr of this capacitor appea rs in series with the supply source impedance and lowers overall efficiency. this capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the input supply. a minimum value of 4.7f is acceptable if the input source is close to the device, but higher values will improve performance a t lower input voltages, especially when the source impedance is high. the input capacitor should be placed as cl ose as possible to the ic. for maximum stability over temperature and voltage, capacitors wi th x7r, x5r, or better dielectric are recommended. capacitors with y5vdielectric are not suitable for decoupli ng in this application and should not be used. inductor selection recommended inductor values for the pam2861 are in the range 33h to 100h. higher values of induc tance are recommended at high er supply voltages in order to minimize errors due to switching delays, which in increased ripple and lower efficiency. higher val ues of inductance also result in a smaller change in output current over the s upply voltage range. the inductor should be mounted as close to the device as possilbe with low resistance connections to the lx and vin pins. the chosen coil s hould have a saturation current higher than t he peak output current and a continuous current rating above the required mean output current. the inductor value should be chosen to maintain operating duty cy cle and switch ?on?/?off? times within the specified limits ov er the supply voltage and load current range. the following equations can be used as a guide. lx switch ?on? time ) rrr ( ivv il t lxlsled led in on ???? ? ? lx switch ?off? time ) rr ( ivv il t lsleddled off ??? ? ? where: l is the coil inductance; r l is the coil resistance; r s is the current sense resistance i led is the required led current; ? i is the coil peak- peak ripple current (internally set to 0.25 x i led ); v in is the supply voltage; v led is the total led forward voltage; r lx is the switch resistance (0.3 nominal); v d is the diode forward voltage at the required load current
pam2861 document number: dsxxxxx rev. 1 - 1 9 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated application information (cont.) diode selection for maximum efficiency and performance, the rectifier (d1) should be a fast low capac itance schottky diode with low reverse lea kage at the maximum operating voltage and temperature. they also provide be tter efficiency than silicon diodes, due to a combination of low er forward voltage and reduced recovery time. it is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher t han the maximum output load current. it is very important to consider the re verse leakage of the diode when operating above +85c. excess leaka ge will increase the power dissipation in the device and if close to the load may create a thermal runaway condition. the higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on the l x output. if a silicon diode is used, care should be tak en to ensure that the total voltage appearing on the lx pin including supply ripple, d oes not exceed the specified maximum value. ordering information part number part marking package type standard package pam2861abr eqxyw tsot25 3000 units/ tape&reel PAM2861CBR p2861 xxxyw sot89-5 1000 units/ tape&reel marking information top view tsot25
pam2861 document number: dsxxxxx rev. 1 - 1 10 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated package outline dimensions (all dimensions in mm.) tsot25
pam2861 document number: dsxxxxx rev. 1 - 1 11 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated package outline dimensions (cont.) (all dimensions in mm.) sot89-5
pam2861 document number: dsxxxxx rev. 1 - 1 12 of 12 www.diodes.com july 2013 ? diodes incorporated pam2861 a product line o f diodes incorporated important notice diodes incorporated makes no warranty of any kind, express or implied, with regards to this document, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose (and their equivalents under the laws of any jurisdiction). diodes incorporated and its subsidiaries rese rve the right to make modifications, enhanc ements, improvements, corrections or ot her changes without further notice to this document and any product descri bed herein. diodes incorporated does not assume any liability arising out of the application or use of this document or an y product described herein; neither does di odes incorporated convey any license under its patent or trademark rights, nor the rights of others. any customer or us er of this document or products described herein in such applica tions shall assume all risks of such use and will agree to hold diodes incorporated and all the companies whose products are represented on diodes incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthoriz ed sales channel. should customers purchase or use diodes inco rporated products for any unintended or una uthorized application, customers shall i ndemnify and hold diodes incorporated and its representativ es harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death a ssociated with such unintended or unauthorized application. products described herein may be covered by one or more united states, international or foreign patents pending. product names and markings noted herein may also be covered by one or more united states, international or foreign trademarks. this document is written in english but may be translated into multiple languages for reference. only the english version of t his document is the final and determinative format released by diodes incorporated. life support diodes incorporated products are specifically not authorized for use as critical component s in life support devices or systems without the express written approval of the chief executive offi cer of diodes incorporated. as used herein: a. life support devices or syst ems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when proper ly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. b. a critical component is any component in a life support devic e or system whose failure to perform can be reasonably expect ed to cause the failure of the life support device or to affect its safety or effectiveness. customers represent that they have all necessary expertise in the safety and regulatory ramifi cations of their life support dev ices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-rel ated requirements concerning the ir products and any use of diodes incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or s ystems-related information or support that may be provided by diodes incorporated. further, customers must fully indemnify diodes incorporate d and its representatives against any damages arisi ng out of the use of diodes incorporated pr oducts in such safety-critical, life suppor t devices or systems. copyright ? 2013, diodes incorporated www.diodes.com

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