EUP2983 ds2983 ver1.2 nov. 2008 1 white led driver for buck-boost application description the EUP2983 is a constant current boost converter specially designed for driving white leds with wide input range. the unique converter topology provide a load voltage which can be greater or less than the input voltage. with the tightly regulated load current, the EUP2983 allows series connection with multiple strings of the white leds. the brightness of the leds can be adjusted through a voltage level on the ctrl pin or by applying a pwm signal to ctrl pin. 1mhz current-mode, pulse-width modulated (pwm) operation allows for small input and output capacitors and a small inductor while minimizing ripple on the input supply/battery. programmable soft-s tart eliminates inrush current during startup. the EUP2983 is available in a space-saving, 8-pin 3mm x 3mm tdfn package. typical application circuit features z 6v to 25v input range z 32v (typ.) output with overvoltage protection z up to 90% efficiency z flexible analog or pwm dimming control z internal high power mosfet switch z 1mhz pwm operation z small, low-profile inductors and capacitors z 3mm 3mm tdfn-8 package z rohs compliant and 100% lead (pb)-free applications z 7~10 inch white led display backlighting z 12v automotive display system z pdvd and subnotebooks z led lighting figure 1. high brightness leds application
EUP2983 ds2983 ver1.2 nov. 2008 2 typical application circuit figure 2. wled backlight application pin configurations package type pin configurations tdfn-8 pin description pin tdfn-8 description 1 pgnd power ground 2 in input supply voltage 3 ctrl brightness control input. led brightness is controlled by the voltage applied to ctrl. varying the voltage from 0.24v to 1.68v adjusts the brightness from dim to bright, respectively. any voltage above 1.68v does not increase brightness. 4 fb current-sense feedback input. connect a resistor from fb to in to set the leds bias current, the voltage (v fb -v in ) regulates to v ctrl / 10 or 168mv, whichever is lower. 5 comp compensation input. connect a 0.1f capacitor (c comp ) from comp to gnd. c comp stabilizes the converter and controls soft-start. c comp discharges to gnd when in shutdown. 6 gnd analog ground. 7 ovp over voltage sense. when v ovp is greater than 32v, the internal n-channel mosfet turns off until v ovp drops below 30v, then the ic re-enters soft-start. connect a 2.2f capacitor from ovp to pgnd. 8 lx inductor connection. this pin is high impedance during shutdown.
EUP2983 ds2983 ver1.2 nov. 2008 3 ordering information order number package type markin g operating temperature range EUP2983jir1 tdfn-8 xxxxx p2983 -40 c to +85c EUP2983 ?? ?? ?? ?? lead free code 1: lead free 0: lead packing r: tape & reel operating temperature range i: industry standard package type j: tdfn block diagram figure 3.
EUP2983 ds2983 ver1.2 nov. 2008 4 absolute maximum ratings (1) ? in to gnd -------------------------------------------- ------------------------------ -0.3v to 31v ? pgnd,gnd ------------------------------------------------------------------------ -0.3v to 0.3v ? fb,lx,ovp to gnd ---------------------------------- ---------------------------- -0.3v to 34v ? comp,ctrl to gnd ------------------------------------------------------------- -0.3v to 6v ? i lx ------------------------------------------------------------------------------------- 2a ? package thermal resistance tdfn-8, c ja ------------------------------------------------------------------------- 50c/w ? junction temperature ---------------------------------------------------------------- 150c ? lead temperature (soldering, 10sec.) --------------------------------------------- 260c ? storage temperature range -------------------------------------------------------- -65c to +150c recommend operating conditions (2) ? supply voltage , v in ------------------------------------------------------------------ 6v to 25v ? operation temperature range --------------------- --------------------------------- -40c to +85c note (1): stress beyond those listed under ?absolute maximum ratings? may damage the device. note (2): the device is not guaranteed to function outside the recommended operating conditions. electrical characteristics (v in =8.4v, l 1 =22uh, c in =10f, c out =2.2f, c comp =0.1f, r 1 =7.5, v ctrl =1v, t a =-40c to +85c . refer to figure 2. unless otherwise noted. typical values are at t a = +25c) EUP2983 parameter conditions min typ max. unit supply voltage 6 25 v rising 4.8 5 5.2 v uvlo threshold falling 4.5 4.7 4.9 v continuous switching 1.2 1.8 ma quiescent current shutdown v ctrl =0 120 200 ua rising 32 v ovlo threshold falling 30 v v ovp =30v, v ctrl >0.24v 20 40 60 a ovp input bias current v ovp =v in , v ctrl =gnd 1 a error amplifier ctrl to fb regulation v ctrl =1v, v in =8.4v, temp=25 ?? 90 100 110 mv ctrl input resistance v ctrl 1v 200 500 800 k ? ctrl dual-mode threshold rising and falling 100 180 240 mv ctrl shutdown enable delay 8.2 ms fb-to-comp transconductance v comp =1v 52 s oscillator operating frequency 0.75 1.0 1.25 mhz maximum duty cycle v ctrl =3v,v fb =v in 90 92 95 % n-channel switch lx on-resistance 0.5 1 ? lx current limit duty cycle=90% 0.8 1.4 2 a
EUP2983 ds2983 ver1.2 nov. 2008 5 70 72 74 76 78 80 82 84 86 88 90 92 94 0 5 10 15 20 led current(ma) efficiency(%) 15leds 27leds 3leds 75 77 79 81 83 85 87 89 91 93 95 0 5 10 15 20 led current(ma) efficiency(%) vin=6v vin=8.4v vin=15v 0 2 4 6 8 10 12 14 16 18 20 22 0 102030405060708090100 duty cycle(%) led current(ma ) typical operating characteristics v in =8.4v driving multiple strings led led current vs. direct-pwm dimming (f ctrl =1khz) v in =8.4v driving 1 string of 3 leds driving 9 strings of 3 leds soft-start and shutdown v in =8.4v driving 5 strings of 3 leds
EUP2983 ds2983 ver1.2 nov. 2008 6 typical operating characteristics (continued) v in =8.4v driving 9 strings of 3 leds direct-pwm dimming waveform (f ctrl =1khz) v in =8.4v ctrl step response direct-pwm dimming waveform (f ctrl =100khz)
EUP2983 ds2983 ver1.2 nov. 2008 7 application information soft-start the EUP2983 attains soft-start by charging c comp gradually with a current source. when v comp rises above 1.25v, the internal mosfet begins switching at a incremental duty cycle. when v comp rises above 2.25v, the duty cycle is at its maximum. see the typical operating characteristics for an example of soft-start operation. shutdown the EUP2983 enters shutdown when v ctrl is less than 100mv for more than 8.2ms. in shutdown, supply current is reduced to 150a by powering down the entire ic except for the ctrl voltage-detection circuitry and internal regulator. c comp is discharged during shutdown, allowing the device to reinitiate soft-start when it is enabled. typical shutdown timing characteristics are shown in the typical operating characteristics. overvoltage protection overvoltage lockout (ovlo) occurs when v out is above 32v.the protection circuitry stops the internal mosfet from switching and causes v comp to decay to 0v. the device comes out of ovlo and into soft-start when v out falls below 30v. in normal operation, EUP2983 v out calculates as follows: k led v fb v in v out v + + = where k----------number of leds in each string v in --------input voltage v fb --------feedback voltage v led -------a led forward voltage adjusting led current adjusting the EUP2983?s output current changes the brightness of the leds. an analog input ctrl and the sense-resistor value set the output current. output current is given by: the v ctrl voltage range for adjusting output current is 0.24v to 1.68v. to set the maximum current, calculate r sense when v ctrl is at its maximum as follows: power dissipation in r sense is typically less than 10mw, making a standard chip resistor sufficient. pwm dimming control ctrl is also used as a digital input allowing led brightness control with a logic-level pwm signal applied directly to ctrl. the frequency range is from 200hz to 200khz, while 0% duty cycle corresponds to zero current and 100% duty cycle corresponds to full current. the error amplifier and compensation capacitor form a lowpass filter so pwm dimming results in dc current to the leds without the need for any add itional rc filters; see the typical operating characteristics. capacitor selection the exact values of input an d output capacitors are not critical. the typical value for the input capacitor is 10f and the typical value for the output capacitor is 2.2f. larger value capacitors can be used to reduce input and output ripple, but at the expense of size and higher cost. c comp stabilizes the converter and controls soft-start. connect a 0.1f capacitor from comp to gnd. inductor selection inductor values range from 10h to 47h. a 22h inductor optimizes the efficiency for most applications while maintaining low 50mv p-p input ripple. to prevent core saturation, ensu re that the inductor-saturation current rating exceeds the peak inductor current for the application. calculate the peak inductor current with the following formula: schottky diode selection the EUP2983?s high switching frequency demands a high-speed rectification diode (d1) for optimum efficiency. a schottky diode is recommended due to its fast recovery time and low forward-voltage drop. ensure that the diode?s average and peak current ratin g exceed the average output current and peak inductor current. in addition, the diode?s reverse breakdown voltage must exceed v out . the rms diode current can be calculated from: pc board layout due to fast switching waveforms and high-current paths, careful pc board layout is required. an evaluation kit is available to speed design. when laying out a board, minimize trace lengths between the ic and r sense , the inductor, the diode, the input capacitor, and the output capacitor. keep traces short, direct, and wide. keep noisy traces, such as the lx node trace, away from fb. the in bypass capacitor (c in ) should be placed as close to the ic as possible. pgnd and gnd s hould be connected directly to the exposed paddle underneath the ic. the ground connections of c in and c out should be as close together as possible. the traces from in to the inductor and from the schottky diode to the leds may be longer. () max led i 10 1.68 sense r = sense r 10 ctrl v led i = () () () () l 2 s 0.9 min in v min in v 0.9 max led i max out v peak i + = () peak i out i rms diode i =
EUP2983 ds2983 ver1.2 nov. 2008 8 packaging information tdfn-8 detail a millimeters inches symbols min. max. min. max. a 0.70 0.80 0.028 0.031 a1 0.00 0.05 0.000 0.002 b 0.20 0.40 0.008 0.016 d 2.90 3.10 0.114 0.122 d1 2.30 0.090 e 2.90 3.10 0.114 0.122 e1 1.50 0.059 e 0.65 0.026 l 0.25 0.45 0.010 0.018
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