PAM2804 document number: ds 36403 rev. 3 - 2 1 of 10 www.diodes.com september 2015 ? diodes incorporated PAM2804 1a step - down constant current, high efficiency led driver description the PAM2804 is a step - down constant current led driver. when the input voltage is down to lower than led forward voltage, then PAM2804 goes into ldo mode. the PAM2804 supports a range of input voltages from 2.5v to 6.0v, allowing the use of a single li+/li - polymer cell, 3aa or 4aa cell, usb, and other standard power sources. the fb voltage is only 0.1v to achieve high efficiency. PAM2804 employ s internal power switch and synchronous rectifier to minimize external part count and realize high efficiency. during shutdown, the input is disconnected from the output and the shutdown current is less than 1 a. other key features include under voltage lockout to prevent deep b attery discharge of the li+ battery. features ? efficiency up to 93% ? 180a(typ ) quiescent current ? output current: up to 1a ? internal synchronous rectifier ? 1.5mhz switching frequency ? soft - start ? under v oltage lockout ? short led protection ? open led protection ? thermal shutdown ? 5 - p in small t sot25 packages ? pb - free package pin assignments applications ? 3aa or 4aa batteries powered flashlight ? 1 cell li - ion battery powered flashlight typical applications circuit i led = 0.1/r s top view tsot25
PAM2804 document number: ds 36403 rev. 3 - 2 2 of 10 www.diodes.com september 2015 ? diodes incorporated PAM2804 pin description pin number pin name function 1 en enable cont rol input. force this pin voltage above 1.5v, enables the chip, and below 0.3v shuts down the device. 2 gnd ground 3 sw the drains of the internal main and s ynchronous p ower mosfet. 4 vin chip main power supply pin . 5 fb feedback voltage to intern al error amplifier, the threshold voltage is 0.1v. block diagram absolute maximum ratings (@ t a = +25c, unless otherwise specified.) these are stress rat ings only and functional operation is n ot implied. exposure to absolute maximum ratings for prolonged time periods may affect device re liability. all voltages are with respect to ground . parameter rating unit input pin voltage - 0.3 to +6.5 v en, fb pi n voltage - 0.3 to v in sw pin voltage - 0.3 to (v in +0.3) junction temperature range 150 c storage temperature range - 65 to +150 soldering temperature + 300, 5sec
PAM2804 document number: ds 36403 rev. 3 - 2 3 of 10 www.diodes.com september 2015 ? diodes incorporated PAM2804 recommended operating conditions (@ t a = +25c, unless otherwise specified. ) parameter rating unit supply voltage 2.5 to 6.0 c operation temper a ture range - 40 to +85 junction temperature range - 40 to +125 thermal information parameter symbol package max unit thermal resistance (junction to case) jc t sot2 5 (note 1) 130 c/w thermal resistance (junction to ambient) ja t sot2 5 250 internal power dissipation p d t sot2 5 400 mw note: 1. the maximum output current for t sot25 package is limited by internal power dissipation capacity as described in application information herein after. electrical characteristics (@ t a = +25c, v in = 4.2 v, real wled load, l = 4.7 h, c in = 1 0 f, c o = 10 f , unless otherwise specified.) parameter symbol test conditions min typ max units input voltage range v in - 2.5 - 6.0 v regulated feedback voltage v fb - 0.095 0.100 0.105 v peak inductor current i pk v in = 5v - 1.5 - a quiescent current i q no load - 180 - a shutdown current i sd v en = 0v - - 1 a oscillator frequency f osc v o = 100% 1.2 1.5 1.8 mhz drain - source on - state resistance r ds(on) i ds = 100ma p mosfet - 0.30 0.45 ? n mosfet - 0.35 0.50 ? sw leakage current i lsw - - 0.01 1 a high efficiency - - 93 - % en threshold high v eh - 1.5 - - v en threshold low v el - - - 0.3 v en leakage current i en - - 0.01 - a over - temperature protection otp - - + 150 - c otp hysteresis oth - - + 30 - c
PAM2804 document number: ds 36403 rev. 3 - 2 4 of 10 www.diodes.com september 2015 ? diodes incorporated PAM2804 typical performance characteristics ( @ t a = +25c, l = 4.7 f, c in = 10f, c o = 10 f , unless otherwise specified.)
PAM2804 document number: ds 36403 rev. 3 - 2 5 of 10 www.diodes.com september 2015 ? diodes incorporated PAM2804 typical performa nce characteristics (cont.) @ t a = +25c, l = 4.7 f, c in = 10f, c o = 10f, unless otherwise specified.) start up with enable pwm dimming: iled vs. duty cycle
PAM2804 document number: ds 36403 rev. 3 - 2 6 of 10 www.diodes.com september 2015 ? diodes incorporated PAM2804 application information pwm dimming the pam2 8 04 can be used to dim led current dimming by driving the en pin via pwm waveform . the sw pin current is then effectively switched on and off causing the led current to turn on and off. the recommended pwm frequency is 500hz (see figure on page 5 for details) . inductor selection the basic PAM2804 application circuit is shown in page 1. external component selection is determined by the load requirement, selecting l first and then c in and c out . for most applications, the value of the inductor will fall with i n the range of 1h to 4.7h. its value is chosen based on the desired ripple current. large value inductors lower ripple current and small value inductors result in higher ripple currents. higher v in or v out also increases the ripple current as shown in eq uation 1. a reasonable starting point for setting ripple current is i l = 400ma (40% of 1a). equation (1) the dc current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. thus, a 1.4a rated inductor should be enough for most applications (1a + 400ma). for better efficiency, choose a low dc - resistance inductor. using ceramic input output capacitors higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. their high ripple current, high voltage rating and low esr make them ideal for switching regulator applications. using ceramic capacitors can achieve very low output ripple and small circuit siz e. when choosing the input and output ceramic capacitors, choose the x5r or x7r dielectric formulations. these dielectrics have the best temperature and voltage characteristics of all the ceramics for a given value and size. thermal c onsideration thermal protection limits power dissipation in the PAM2804. when the junction temperature exceeds + 150c, the otp (over t emperature protection) starts the thermal shutdown and turns the pass transistor off. the pass transistor resumes operation after the junctio n temperature dro ps below +120 c. for continuous ope r ation, the junctio n temperature should be maintained below + 125c. the power dissipation is defined as: i q is the step - down converter quiescent current. the term tsw is used to estimate the full load step - down converter switching losses. for the condition where the step - down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? v v 1 v l f 1 i in out out l ? ? ? ? v i i f t v r v v r v i p in q o s sw in l ) on ( ds o in h ) on ( ds o 2 o d ? ? ? ? ? v i r i p in q h ) on ( ds 2 o d ? ?
PAM2804 document number: ds 36403 rev. 3 - 2 7 of 10 www.diodes.com september 2015 ? diodes incorporated PAM2804 application information (cont.) since r ds(o n) , quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. the maximum power dissipation depends on the thermal resistance of ic package, pcb layout, the rate of s urrounding airflow and temperature difference between junction and ambient. the maximum power dissipation can be calculated by the following formula: where t j( max ) is the maximum allowable junction temperature + 125c. t a is the amb ient temperature and ja is the thermal resistance from the junction to the ambient. based on the standard jedec for a two layers thermal test board, the thermal resistance ja of t sot25 package is 250c/w. the maximum power dissipation at t a = + 25c can b e calculated by following formula: setting the output current the internal feedback (fb) voltage is 0.1v (typical). the output current is calculated as below: the output current is given by the following t able. r s (?) led (ma) 0.286 350 0.143 700 0.1 1 , 000 as the input voltage approaches the led forward vo ltage, the PAM2804 turns the p - c han nel transistor continuously on. in this mode , the v oltage drop on led is equal to the input voltage minus the voltage dro p across the p - c hannel transistor, inductor and current resistor: w here r ds(on) = p - c hannel switch on resistance, iled = led current, r l = inductor dc r esistance, r s = inductor dc r esistance. thermal shutdown when the die tempera ture exceeds + 150c, a reset occurs and the reset remains until the temperature decrease to + 120c, at which time the circuit can be restarted. pcb layout check list when laying out the printed circuit board, the following checklist should be used to ensu re proper operation of the PAM2804. these items are also illustrated graphically in figure 1. check the following in your layout: 1. the power traces, consisting of the gnd trace, the sw trace and the vin trace should be kept short, direct and wide. 2. doe s the v fb pin connect directly to the current sense resistor? the current sense resistor to gnd trace should be kept short, direct and wide. 3. does the (+) plate of c in connect to v in as closely as possible? this capacitor provides the ac current to the i nternal power mosfets. 4. keep the switching node, sw, away from the sensitive vfb node. 5. keep the ( C ) plates of c in and c out as close as possible. ? ? ? ja a ) max ( j d t t p ? ? w w c c c p d 4 . 0 / 250 / 25 125 ? ? ? ? ? ? r / 1 . 0 i s led ? ? ? r r r iled v v s l ) on ( ds in leddrop ? ? ? ?
PAM2804 document number: ds 36403 rev. 3 - 2 8 of 10 www.diodes.com september 2015 ? diodes incorporated PAM2804 ordering information part number marking package type st andard package PAM2804 aa b010 refer to marking information below t sot2 5 3 , 000 units/tape & reel marking information top view tsot25 p a m 2 8 0 4 x x x x x x p i n c o n f i g u r a t i o n b : 5 a t y p e : 1 . e n 2 . g n d 3 . s w 4 . v i n 5 . f b a : t s o t 2 5 p a c k a g e t y p e n u m b e r o f p i n s f b v o l t a g e 0 1 0 : 0 . 1 v
PAM2804 document number: ds 36403 rev. 3 - 2 9 of 10 www.diodes.com september 2015 ? diodes incorporated PAM2804 package outline dimensions tsot25 tsot25 dim min max typ a - ? 1.00 - a1 0.01 0.10 - a2 0.84 0.90 - b 0.30 0.45 - c 0.12 0.20 - d - - 2.90 e - - 2.80 e1 - - 1.60 e 0.95 bsc e1 1.90 bsc l 0.30 0.50 l2 0.25 bsc 0 8 4 1 4 12 - all dimensions in mm suggested pad layout tsot25 dimensions value (in mm) c 0.950 x 0.700 y 1.000 y1 3.19 9 d e1 e1/2 e1 e e/2 e a a2 a1 seating plane 0 l2 l gauge plane 01(4x) 01(4x) c b seating plane y1 c x y
PAM2804 document number: ds 36403 rev. 3 - 2 10 of 10 www.diodes.com september 2015 ? diodes incorporated PAM2804 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 eq uivalents under the laws of any jurisdiction). diodes incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes without further notice to this document and any product described h erein. diodes incorporated does not assume any liability arising out of the application or use of this document or any product described herein; neither does diodes incorporated convey any license unde r its patent or trademark rights, nor the rights of oth ers. any customer or user of this document or products described herein in such applications shall assume all risks of such use and will agree to hold diodes incorporated and all the companies whose products are represented on diod es incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthor ized sales channel. should customers purchase or use diodes incorporated products for any uninte nded or unauthorized application, customers shall indemnify and hold diodes incorporated and its representatives harmless against all claims, damages, expenses, and attorney f ees arising out of, directly or indirectly, any claim of personal injury or death associated 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 unit ed 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 this document is the final and determinative format released by diodes incorporated. life support diodes incorporated products are specifically not authorized for use as critical components in life support devices or system s w ithout the express written approval of the chief executive officer of diodes incorporated. as used herein: a. life support devices or systems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and wh ose failure to perform when properly 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 device or system whose failure to perform can be reasonably expected 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 ramificat ions of their life support devices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety - related requirements concerning their products and any use of diodes incorporated products in such safety - critica l, life support devices or systems, notwithstanding any devices - or systems - related information or support that may be provided by diodes incorporated. further, customers must fully indemnify diodes incorpora ted and its representatives against any damages arising out of the use of diodes incorporated products in such safety - critical, life support devices or systems. copyright ? 201 5 , diodes incorporated www.diodes.com
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