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| pam2842 document number: dsxxxxx rev. 1 - 2 1 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated high power led driver description the pam2842 is a high power led driv er, capable of driving up to 10 high power leds in series. the pam2842 supports buck, boost and sepic topology. the pam2842 features over current protection, over voltage protection, under voltage lockout and over temperature protection, which prevent the device from damage. led dimming can be done by using a pwm signal to the comp pin. the pam2842 is available in tssop-20 packages. features ? output power up to 30w ? chip enable with soft-start ? analog and pwm dimming ? peak efficiency up to 97% ? low quiescent current ? switching frequency adjustable ? support buck/boost/sepic toplogy ? over current protection ? over voltage protection ? thermal protection ? uvlo ? tiny pb-free packages: 40-pin qfn6x6 and tssop-20 applications ? home lighting ? automotive lighting ? monitor backlighting pin assignments
pam2842 document number: dsxxxxx rev. 1 - 2 2 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated typical applications circuit boost with low side current sense boost with high side current sense buck/boost (sepic) with low side current sense buck/boost (sepic) with high side current sense buck with high side current sense pam2842 document number: dsxxxxx rev. 1 - 2 3 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated pin descriptions pin name pin number function qfn6x6-40 tssop-20 pgnd 1 ? 6 1, 2, 3, 4, 10, 11 power ground hvin 8 5 input en 9 6 chip enable, active high vdd-dr 10 7 internal ldo output rt 12 8 frequency adjustment pin agnd 13 9 analog ground sense- 14 12 sense resistor - sense+ 15 13 sense resistor+ comp 17 14 compensation node vdd_5v 21 15 internal ldo output ov 23 16 over voltage sw 25 ? 30 17, 18, 19 drain of main switch nc 7, 11, 16, 18-20, 22, 24, 31-40 20 not connected functional block diagram pam2842 document number: dsxxxxx rev. 1 - 2 4 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated 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 supply voltage 40 v buck application maximum output current 3 a i/o pin voltage range gnd -0.3 to v dd +0.3 v maximum junction temperature 150 c storage temperature -40 to +150 soldering temperature 300, 5sec recommended operating conditions (@t a = +25c, unless otherwise specified.) parameter rating unit supply voltage range 5.5 to 40 v operation temperature range -40 to +85 c junction temperature range -40 to +125 thermal information parameter package symbol max unit thermal resistance (junction to case) tssop-20 jc 20 c/w qfn6x6-40 7.6 (note 1) thermal resistance (junction to ambient) tssop-20 ja 90 qfn6x6-40 18.1 (note 1) note: 1. the exposed pad must be soldered to a thermal land on the pcb. electrical characteristics (@t a = +25c, v en = v dd = 24v, 1w x 10 leds, unless otherwise specified.) parameter test conditions min typ max units input voltage range 5.5 40 v quiescent current e na = high (no switching frequency) 1 2 ma e na = high (1m switching frequency) 6 ma e na = high (500k switching frequency) 3 ma e na = high (200k switching frequency) 1.6 ma e na = low 5 10 a feedback voltage, low side v fb = v sense+ -agnd, v sense- = agnd 95 100 105 mv feedback voltage, high side v fb = v sense+ ? v sense- 95 100 105 mv led current line regulation i o = 350ma 0.02 %/v led current load regulation 1.0 % vdd_dr uvlo hysteresis no switching 200 mv pam2842 document number: dsxxxxx rev. 1 - 2 5 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated electrical characteristics (cont.) (@t a = +25c, v en = v dd = 24v, 1w x 10 leds, unless otherwise specified.) parameter test conditions min typ max units ldo stage vdd_5v no switching 4.5 5 5.5 v vdd_5v current limit no switching 14 74 90 ma vdd_5v uvlo threshold no switching 3.7 4.0 4.3 v vdd_5v uvlo hysteresis no switching 200 mv vdd_dr no switching 4.5 5 5.5 v vdd_dr current_limit no switching 14 50 90 ma vdd_dr uvlo threshold no switching 3.7 4.0 4.3 v switch stage switch rds(on) vdd_5v = 5v 0.1 ? switch current limit 3.5 a switch leakage current 50 a rt voltage r rt = 71k ? 1.1 1.2 1.3 v switching frequency (note 2) r rt = 30k ? 800k 1m 1.2m hz r rt = 71k ? 400 500 600 khz r rt = 180k ? 160 200 240 khz min duty cycle f sw = 1mhz 10 % f sw = 500khz 5 % f sw = 200khz 2.5 % max duty cycle low side sense 95 % high side sense 100 % vc source current feedback voltage = 0 30 a vc sink current feedback voltage = 0 30 a fault protection ov threshold voltage 1.1 1.2 1.3 v ov hysteresis 70 mv thermal shutdown 150 c thermal shutdown hysteresis 30 c control interface en high 1.5 v en low 0.4 v note: 2. switching frequency ) k 12 r ( x 24 10 f rt 12 sw + = , reference value. pam2842 document number: dsxxxxx rev. 1 - 2 6 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated typical performance characteristics boost mode, @t a = +25c, v en = v dd = 24v, 3w leds, f sw = 200khz, unless otherwise specified.) pam2842 document number: dsxxxxx rev. 1 - 2 7 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated typical performance characteristics (cont.) @t a = +25c, f sw = 300khz, unless otherwise specified.) pam2842 document number: dsxxxxx rev. 1 - 2 8 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated application information topology selection when maximum power supply voltage is below than minimum load vo ltage, select the boost topology. when minimum power supply volt age is high than maximum load voltage, select buck topology. when l oad voltage range is small and between the power supply voltage, se lect sepic topology. table 1: voltage condition vs. topology condition topology v inmax < v omin boost v inmin > v omax buck v o pam2842 document number: dsxxxxx rev. 1 - 2 10 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated application information (cont.) diode selection pam2842 is a high switching frequency converter which demands hi gh speed rectifier. it's indis pensable to use a schottky diode rated at 3a, 40v with the pam2842. using a schottky diode with a lower forwar d voltage drop is better to improve the power led efficiency. in boost topology, the voltage rating should be higher than v out and in buck topology, the voltage rating higher than v in , the peak current is 2 i i i l l ) max ( d + = in sepic topology, the voltage rating should be higher than v in +v out , the peak current is i i i ) peak ( 2 l ) peak ( 1 l ) max ( d + = the average current of the diode equals to i o . work frequency selection pam2842 working frequency is decided by resi stor connect to the rt pin, it can be calculated by follow equation: ) hz ( ) k 12 rt ( x 24 10 f 12 sw + = from the equations, we can see when working frequency is high, the inductance can be small. it's important in some size limit a pplication. but we should know when the working frequency is higher, the switching loss is higher too. we must pay attention to thermal dissipa tion in this application. methods for setting led current there are two methods for setting and adjusting the led current: 1) r sense only 2) pwm signal with external components a) use the comp pin b) use the sense pin method 1: led current setting with resistor r sense the most basic means of setting the led cu rrent is connecting a resistor between r sense + and r sense -. the led current is decided by iset resistor r sense . i led = 0.1/ r sense for flowing the large current, must pay attention to power dissipation on the resistor. r sense has two positions to select: high side cu rrent sense and low side current sense. in buck topology it just has high side curren t sense. in other topology we recommend use low side current sense for easier pcb layout. method 2: led current setting wi th pwm signal using comp pin this circuit uses resistor rsense to se t the on state current and the average led current, then proportional to the percentage of off-time when the comp pin is logic high. here use a invert component 2n 7002 (q1) to isolate and invert the pwm signal (see figure 1). figure 1. pwm dimming use comp pin average led current is approximately equal to: t t i t i off on led off avg + = pam2842 document number: dsxxxxx rev. 1 - 2 11 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated also, the recommended pwm frequency is between 100hz and 200hz. application information (cont.) method 2: led current setting with pwm signal using comp pin (cont.) frequency <100hz can cause the leds to blink visibly. as the co mp pin connects to a capacitor , it needs rise time. if frequency >200hz, the average led current will have a large error when duty cycle is small (<50%). it maybe generate the audible noise in this dimming condition. method 3: led current setting with pwm signal using sense pin this method is turn pwm signal to dc voltage, the output current can be adjusted. because the le d current is a adjustable dc va lue, it will cause led color drift. low side current sense and high side current sense circuit is different. please see figure 2 and 3. it use the internal referen ce voltage, so pwm dimming signal voltage is not considered, just m eet the request of the mosfet driving voltage. figure 2. pwm dimming use sense pin in low side current sense figure 3. pwm dimming use sense pin in high side current sense the rc filter (r1,r2,c1,c2) value is decided by dimming frequency, the divider resistor (r3,r4) is decided by dimming range. because final adjusted is a dc value, this method can avoid audible noise effectiv ely and achieve better emi performance than t he second method. setting the output limit voltage the ov pin is connected to the center tap of a resistive vo ltage divider from the high-voltage output to ground (see applicatio n schematic). ) r r 1 ( v v down up ov limit out + = ? the recommend procedure is to choose r3 = 360k and r4 = 12k to set v out_limit = 37.2v. in boost and sepic circuit, when led open or no load, the circuit will have no feedback, if no other measure be taken the switc h voltage will be very high and damage the switch, so this ov pin must be set carefully. in buck circuit, the switch voltage is always small than input volt age, so the ov pin setting is not important in this conditio n. this ov pin is used to limit output voltage to avoid breakdown of the switch other than to regulate output voltage. the setting value must keep the switch voltage below 40v. in sepic circuit, one must notice that the switch voltage equals v in +v o . this ov pin has a hysteresis voltage detect function, not la tch-up function, so output voltage will have a overshoot when no lo ad or load working voltage is high than setting limit voltage. if the component paramet er not match appropriately, the overshoot voltage will be t oo high and can demage the switch. pam2842 document number: dsxxxxx rev. 1 - 2 12 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated application information (cont.) setting the output limit voltage (cont.) several methods can decrease the overshoot voltage: (1) add a small capacitor (<100pf) parallel with the up divider resistor (see figure 4). (2) use external zener to clamp the output peak voltage (see figure 5). figure 4. add forward capacitor figure 5. use external zener note: the output limit voltage must be set higher than working out put voltage by a proper value, or it will work abnormal in lo w temperature or some other conditions. short led function pam2842 is a constant current driver. when one or more led shor ted, the circuit will still work, the output voltage is decided by led numbers. in boost topology, make sure the output voltage is higher than input voltage; otherwise the unlimited current will directly go through supply to led and damage the led. power dissipation as pam2842 integrates a power mosfet, the power dissipation must be considered. to a mosfet the power loss includes 5 sections, turn on loss, turn off loss, conduction loss, dr ive loss and output capacitor coss loss. f t v i 2 1 p r out on turn on turn ? ? = f t v i 2 1 p r out on turn off turn ? ? = r i p ) on ( ds 2 rms ) on ( rds = f u q p drive g drive = = p p p ff p p p coss drive ) on ( rds turne on turn switch + + + + = ? p t switch ja = tr: switch rise time. tf: switch fall time. u drive : gate drive voltage. ja is relative with ic package, heat -sink area and air flow condition etc. above description does not consider the ic control power, so the total power will be more than calculated value. pam2842 has over-temperature protection. when junction temperature is over +150c, it will shut down and auto restart when junc tion temperature decrease below +120. in high temperature circumstance application, one must pay attention to heat dissipation, or it will shut down and restart. it is recommended to use external heat-sink and placed near to the ic surface. pam2842 document number: dsxxxxx rev. 1 - 2 13 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated application information (cont.) pcb layout guidelines careful pcb layout is important for normal operation. use the following guidelines for good pcb layout: (boost) 1) minimize the area of the high current switching loop of the rectifier diode and output capacitor to avoid excessive switchin g noise. 2) connect high-cur rent input and output components with shor t and wide connections. the high-curr ent input loop goes from the positive terminal of the input capacitor to the inductor and the sw pin. the high-current output loop is from the positive terminal of the input capacitor through the inductor, rectifier diode, and positive terminal of the output capacitors, reconnecting between the output capa citor and input capacitor ground terminals. avoid usi ng vias in the highcurrent paths. if vias are unavoidable, use multiple vias in parall el to reduce resistance and inductance. 3) create a ground island (pgnd) consis ting of the input and output capacitor grou nd and pgnd pin. connect all these together w ith short, wide traces or a small ground plane. maximizing the width of the power ground traces improves efficiency and reduc es output-volt age ripple and noise spikes. create an analog ground island (agnd) consisting of the output vo ltage detection-divider ground connection, t he sense-pin connection, v cc -5v and v cc -driver capacitor connecti ons. connect the device's exposed backside pad to pgnd. make sure no other connections between these separate ground planes. 4) place the output voltage setting-divider re sistors as close to the ov pin as possi ble. the divider's center trace should be kept short. avoid running the sensing traces near sw pin. 5) place the vin pin bypass capacitor as close to the device as possible. the groun d connection of the vin bypass capacitor sho uld be connected directly to gnd pins with a wide trace. 6) minimize the size of the sw node while keeping it wide and short. keep the sw node away from the feedback node. if possible, avoid running the sw node from one side of the pcb to the other. 7) for the good thermal dissipation, pam2842 has a heat dissipate pad in the bottom side, it should be soldered to pcb surface. as the copper area cannot be large in the component side, we can use multiple vias connecting to other side of the pcb. 8) refer to the example of a pam2842 evaluation board layout below. tssop-20 boost qfn6x6-40 boost pcb layout example pam2842 document number: dsxxxxx rev. 1 - 2 14 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated ordering information part number package type standard package pam2842rgr tssop-20 1000 units/tape&reel PAM2842TJR qfn6x6-40 1000 units/tape&reel marking information pam2842 document number: dsxxxxx rev. 1 - 2 15 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated package outline dimensions (all dimensions in mm.) tssop-20 pam2842 document number: dsxxxxx rev. 1 - 2 16 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 a product line o f diodes incorporated package outline dimensions (cont.) (all dimensions in mm.) qfn6x6-40 pam2842 document number: dsxxxxx rev. 1 - 2 17 of 17 www.diodes.com october 2012 ? diodes incorporated pam2842 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 ari sing 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 w hatsoever 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 ? 2012, diodes incorporated www.diodes.com |
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