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four-string white led driver data sheet add5205 rev. 0 information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781.329.4700 www.analog.com fax: 781.461.3113 ?2011 analog devices, inc. all rights reserved. features white led driver based on inductive boost converter input voltage range: 2.8 v to 18 v internal compensation 1 mhz fixed operating frequency 28 v fixed overvoltage protection built-in soft start for boost converter drives up to 4 led current sources led current adjustable up to 25 ma for each channel dc current level brightness control with pwm input led open fault protection general thermal shutdown undervoltage lockout 12-lead, 3 mm 3 mm 0.75 mm lfcsp package applications smart pcs, pmps, tablet pcs, umpcs, and notebooks functional block diagram step-up switching regulator 4-channel current sources brightness control logic undervoltage lockout soft start thermal protection overvoltage protection autodisable for led open 09858-001 figure 1. general description the add5205 is a white led driver for backlight applications based on high efficiency, current mode, step-up converter technology. it is designed with a 0.3 internal switch and 1 mhz fixed operating frequency. the add5205 contains four regulated constant current sources for uniform brightness intensity. each current source is capable of driving up to 25 ma. the add5205 has four parallel strings of multiple series connected leds with 2% current matching. the device provides adjustable current sources that drive up to 25 ma using an external resistor. the led current can be controlled by a pwm signal input on the pwm pin. an internal circuit translates the pwm signal to an analog signal with an external capacitor and linearly controls the led current. the add5205 has multiple safety protection features to prevent any damage during fault conditions. if one or more leds are open, the device disables the faulty current regulator automatically. the internal soft start prevents inrush current during startup. a thermal shutdown protection feature prevents thermal damage. the add5205 is available in a low profile, thermally enhanced 3 mm 3 mm 0.75 mm, 12-lead lead frame chip scale package (lfcsp) and is specified over the temperature range of ?25c to +85c.
add5205 data sheet rev. 0 | page 2 of 16 table of contents features .............................................................................................. 1 ? applications....................................................................................... 1 ? functional block diagram .............................................................. 1 ? general description ......................................................................... 1 ? revision history ............................................................................... 2 ? functional block diagram .............................................................. 3 ? specifications..................................................................................... 4 ? absolute maximum ratings............................................................ 6 ? thermal resistance ...................................................................... 6 ? esd caution.................................................................................. 6 ? pin configuration and function descriptions............................. 7 ? typical performance characteristics ..............................................8 ? theory of operation ...................................................................... 10 ? current mode, stepup switching regulator operation........ 10 ? current source............................................................................ 10 ? pwm dimming mode .............................................................. 10 ? safety features ............................................................................ 10 ? external component selection guide..................................... 11 ? layout guidelines....................................................................... 12 ? typical application circuit ........................................................... 13 ? outline dimensions ....................................................................... 14 ? ordering guide .......................................................................... 14 ? revision history 8/11revision 0: initial version
data sheet add5205 rev. 0 | page 3 of 16 functional block diagram uvp ref uvp comp ll ref ll comp pwm comp error amp ref r s q thermal shutdown soft start current sense voltage reference shutdown headroom control current source 1 current source 2 current source 3 current source 4 osc led open fault protection 7 ocp ref ovp ref dcomp dref + + iset vin shdn ovp sw gnd 6 8 v ref generator fb1 fb2 fb3 fb4 pwm c_filter r c c c r sense r_filter r1 r2 1 2 5 4 3 12 11 10 9 8 6 7 09858-003 gm figure 2. functional block diagram
add5205 data sheet rev. 0 | page 4 of 16 specifications v in = 3.7 v, shdn = high, t a = ?25c to +85c, unless otherwise noted. typical values are at t a = 25c. table 1. parameter symbol test conditions/comments min typ max unit supply input voltage range v in 2.8 18 v quiescent current i q v in = 2.8 v to 18 v, not switching 3.4 ma shutdown supply current i sd v in = 2.8 v to 18 v, shdn = 0 v 1 a switch on resistance r ds(on) i sw = 100 ma 0.3 switch current limit i cl 1.9 a leakage current i lkg 1 a oscillator switching frequency f osc 1 mhz maximum duty cycle d max 90 % soft start soft start time 1 1.5 ms current source iset pin voltage v set 1.26 v c_filter pin voltage v c_filter duty = 100% 0.22 v adjustable led current 1 i led 25 ma constant current sink of 20 ma 2 i led20 r set = 130 k 19.6 20 20.6 ma headroom voltage of 20 ma 2 v hr20 r set = 130 k 0.66 v current matching between strings 2 i led = 20 ma ?2 +2 % led current accuracy of 20 ma 2 i led = 20 ma ?3 +3 % current source leakage current 1 a shutdown control shdn voltage high v shdn _high v in = 2.8 v to 18 v 1.5 6 v shdn voltage low v shdn _low v in = 2.8 v to 18 v 0.6 v pwm control pwm input frequency range 1 0.1 khz pwm voltage high v pwm_high v in = 2.8 v to 18 v 1.5 v pwm voltage low v pwm_low v in = 2.8 v to 18 v 0.6 v 1 guaranteed by design. 2 tested at t a = 25c.
data sheet add5205 rev. 0 | page 5 of 16 v in = 3.7 v, shdn = high, t a = ?25c to +85c, unless otherwise noted. typical values are at t a = 25c. table 2. parameter symbol test conditions/comments min typ max unit thermal protection thermal shutdown threshold 1 tsd 160 c thermal shutdown hysteresis 1 tsd hyst 30 c uvlo uvlo rising threshold v uvlor v in rising 2.5 v uvlo falling threshold v uvlof v in falling 2 v overvoltage protection overvoltage threshold on ovp pin v ovp 28 v 1 guaranteed by design.
add5205 data sheet rev. 0 | page 6 of 16 absolute maximum ratings t a = 25c, unless otherwise noted. table 3. parameter rating vin ?0.3 v to +20 v sw ?0.3 v to +32 v shdn , ?0.3 v to +7 v iset, c_filter ?0.3 v to +3.6 v pwm ?0.3 v to +7 v fb1, fb2, fb3, fb4 ?0.3 v to +32 v ovp ?0.3 v to +32 v maximum junction temperature (t j max) 150c operating temperature range (t a ) ?25c to +85c storage temperature range (t s ) ?65c to +150c reflow peak temperature (20 sec to 40 sec) 260c stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. thermal resistance ja is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. table 4. thermal resistance package type ja jc unit 12-lead lfcsp 41.6 7.65 c/w esd caution
data sheet add5205 rev. 0 | page 7 of 16 pin configuration and fu nction descriptions vin shdn notes 1. connect the exposed paddle to ground. gnd fb4 c_filter iset sw ovp pw m fb1 fb2 fb3 (not to scale) 09858-002 9 8 7 1 2 3 4 5 6 12 11 10 top view add5205 figure 3. pin configuration table 5. pin function descriptions pin o. nemonic description 1 vin supply input pin. bypassed with a capacitor to ground. 2 shdn shutdown control pin for enabling ic. active low. 3 gnd ground pin. 4 sw drain connection of the internal power fet pin. 5 ovp overvoltage protection sense input pin. must be locally bypassed with a 100 nf capacitor and placed as close as possible to the ic. 6 pwm pwm signal input pin. 7 iset full-scale led current set pin. a resistor from this pin to ground sets the led current up to 25 ma. 8 c_filter filtered pwm signal output pin. connect a capacitor between c_filter and ground. this capacitor forms a low-pass filter with an internal resistor. 9 fb4 regulated current sink input pin. connect the bottom cathode of the led string to this pin. if unused, connect fb4 to ground. 10 fb3 regulated current sink input pin. connect the bottom cathode of the led string to this pin. if unused, connect fb3 to ground. 11 fb2 regulated current sink input pin. connect the bottom cathode of the led string to this pin. if unused, connect fb2 to ground. 12 fb1 regulated current sink input pin. connect the bottom cathode of the led string to this pin. this channel should be connected to leds as a default channel. epad connect the exposed paddle to ground.
add5205 data sheet rev. 0 | page 8 of 16 typical performance characteristics 0 10 20 30 40 50 60 70 80 90 100 051 0 input voltage (v) boost converter efficiency (%) 15 20 0 9858-004 0 5 10 led current (ma) 15 20 25 051 0 input voltage (v) 15 20 09858-007 figure 4. boost converter efficiency vs. input voltage, i led = 20 ma, brightness = 100%, and leds = 6 series 4 parallel figure 7. led current vs. input voltage (i led = 22 ma) 0 5 10 led current (ma) 15 25 20 30 0 400 800 r set (k ? ) 1200 1400 200 600 1000 1600 09858-005 ?20 ?15 ?10 ?5 0 5 10 15 20 02 04 0 pwm input duty cycle (%) led current m a tching (%) 60 80 100 09858-008 figure 8. led current matching vs. pwm input duty cycle figure 5. led current (i led ) vs. r set 09858-009 v in = 3.7v brightness = 100% 6 series x 4 parallel a ch3 960mv 1 2 4 3 v out (10v/div) shdn (3v/div) i l (500ma/div) v sw (10v/div) 0 20 18 16 14 12 10 led current (ma) 8 6 4 2 0 20 40 pwm input duty cycle (%) 60 80 100 09858-006 figure 6. led current vs. pwm input duty cycle figure 9. start-up waveforms (brightness = 100%)
data sheet add5205 rev. 0 | page 9 of 16 09858-010 a ch2 11.6v 1 2 4 v out (100mv/div) v sw (10v/div) i l (500ma/div) v in = 18v brightness = 100% 6 series x 4 parallel figure 10. switching waveforms (v in = 18 v) 09858-011 a ch2 11.6v v sw (10v/div) i l (500ma/div) 1 2 4 v out (100mv/div) v in = 3v brightness = 100% 6 series x 4 parallel figure 11. switching waveforms (v in = 3 v) 09858-012 a ch1 840mv 1 2 4 pwm (2v/div) v fb1 (1v/div) i fb1 (10ma/div) v in = 5v brightness = 10% 6 series x 4 parallel figure 12. led current waveforms (brightness = 10%) 0 9858-013 a ch1 840mv 1 v fb1 (1v/div) i fb1 (10ma/div) pwm (2v/div) v in = 5v brightness = 70% 6 series x 4 parallel 2 4 figure 13. led fb1 waveforms (brightness = 70%)
add5205 data sheet rev. 0 | page 10 of 16 theory of operation current mode, stepup switching regulator operation the add5205 uses a current mode pwm boost regulator to provide the minimal voltage needed to enable the led string at the programmed led current. the current mode regulation system allows fast transient response while maintaining a stable output voltage. the regulator response can be optimized for a wide range of input voltages, output voltages, and load conditions. the add5205 can provide a 28 v fixed overvoltage protection voltage and drive up to 6 leds (3.4 v/20 ma type of leds) for four channels from a supply of 3 v or up to 7 leds (3.4 v/20 ma type of leds) for four channels from a supply of 5 v to 18 v. current source the add5205 contains four current sources to provide accurate current sinking for each led string. string-to-string tolerance is kept within 2% at 20 ma. each led string current is adjusted up to 25 ma by an external resistor. the add5205 contains an led open fault protection circuit for each channel. the add5205 recognizes that the current source has an open load fault for the current source, and the current source is disabled. programming the led current as shown in figure 2 , the add5205 has an led current set pin (iset). a resistor (r set ) from this pin to ground adjusts the led current up to 25 ma (see figure 15 ). led current level can be set by )( 2600 a r i set led = pwm dimming mode the add5205 supports pwm input. the internal resistor and external capacitor change the pwm input duty to analog level, and the low-pass filter output adjusts each current source sink current level. dc current dimming in this mode, the maximum led current is set by the value of r set . once the maximum led current is set, the led current can be changed through pwm input. duty = 80% pwmi i led max i led 0a duty = 60% duty = 40% duty = 20% 0.8 i led max 0.6 i led max 0.4 i led max 0.2 i led max 09858-014 figure 14. dc current dimming timing safety features the add5205 contains several safety features to provide stable operation, such as soft start, open load protection (olp), under- voltage lockout (uvlo), and thermal protection. soft start the add5205 contains an internal soft start function to reduce inrush current at startup. the soft start time is typically 1.5 ms. olp the add5205 contains a headroom control circuit to minimize power loss at each current source. therefore, the minimum feed- back voltage is achieved by regulating the output voltage of the boost converter. if any led string is open during normal operation, the current source headroom voltage (v hr ) is pulled to gnd. in this condition, olp is activated. uvlo an undervoltage lockout circuit is included with built-in hysteresis. the add5205 turns on when v in rises above 2.5 v (typical) and shuts down when v in falls below 2 v (typical). thermal protection thermal overload protection prevents excessive power dissipation from overheating the add5205 . when the junction temperature (t j ) exceeds 160c, a thermal sensor immediately activates the fault protection, which shuts down the device, allowing the ic to cool. the device self starts when the t j of the die falls below 130c.
data sheet add5205 rev. 0 | page 11 of 16 external component selection guide inductor selection the inductor is an integral part of the step-up converter. it stores energy during the switch-on time and transfers that energy to the output through the output diode during the switch-off time. an inductor in the 3.3 h to 6.8 h range is recommended. in general, lower inductance values result in higher saturation current and lower series resistance for a given physical size. the input (v in ) and output (v out ) voltages determine the switch duty cycle (d), which in turn can be used to determine the inductor ripple current. out in out v vv d ? = use the duty cycle and switching frequency (f sw ) to determine the on time (t on ). sw on f d t = the inductor ripple current (i l ) in a steady state is l tv i on in l = solve for the inductance value (l). l on in i tv l = ensure that the peak inductor current (that is, the maximum input current plus half of the inductor ripple current) is less than the rated saturation current of the inductor. in addition, ensure that the maximum rated rms current of the inductor is greater than the maximum dc input current to the regulator. l lavg lpk iii 2 1 += , in out out lavg v v i i = out sw in out in l vf vv v l i ? = 1 where: i lpk is the peak inductor current. i lavg is the input average current. table 6 shows a list of recommend inductors. table 6. recommended inductors coilcraft part no. l (h) i sat (a) size (mm) xfl4020-332ml 3.3 2.7 4 4 2 lps4012-472ml 4.7 1.6 3.9 3.9 1.1 lps4018-472ml 4.7 1.8 3.9 3.9 1.7 lps4018-682ml 6.8 1.2 3.9 3.9 1.7 input and output capacitors selection the add5205 requires input and output bypass capacitors to supply transient currents while maintaining a constant input and output voltage. use a low effective series resistance (esr) 4.7 f or greater capa citor for the input capa citor to prevent noise at the add5205 input. place the input between vin and gnd, as close as possible to the add5205 . the output capacitor maintains the output voltage and supplies current to the load while the add5205 switch is on. the value and characteristics of the output capacitor greatly affect the output voltage ripple and stability of the regulator. use a ceramic x5r or x7r dielectric capacitor, and for the output capacitor, a 4.7 f or greater capacitor is preferred. place a 100 nf or greater capacitor as close as possible to the ovp pin of add5205 . diode selection the output diode conducts the inductor current to the output capacitor and loads while the switch is off. for high efficiency, minimize the forward voltage drop of the diode. schottky diodes are recommended. the output diode for a boost regulator must be chosen depending on the output voltage and the output current. the diode must be rated for a reverse voltage greater than the output voltage used. the average current rating must be greater than the maximum load current expected, and the peak current rating must be greater than the peak inductor current.
add5205 data sheet rev. 0 | page 12 of 16 layout guidelines when designing a high frequency, switching, regulated power supply, layout is very important. using a good layout can solve many problems associated with these types of supplies. the main problems are loss of regulation at high output current and/or large input-to-output voltage differentials, excessive noise on the output and switch waveforms, and instability. using the following guidelines can help minimize these problems. make all power (high current) traces as short, direct, and thick as possible. it is good practice on a standard printed circuit board (pcb) to make the traces an absolute minimum of 15 mil (0.381 mm) per ampere. place the inductor, output capacitors, and output diode as close to each other as possible. this helps reduce the emi radiated by the power traces that is due to the high switching currents through them. this also reduces lead inductance and resistance, which in turn reduces noise spikes, ringing, and resistive losses that produce voltage errors. the grounds of the ic, input capacitors, output capacitors, and output diode (if applicable), should be connected close together, directly to a ground plane. it is also a good idea to have a ground plane on both sides of the pcb. this reduces noise by reducing ground loop errors and by absorbing more of the emi radiated by the inductor. due to how switching regulators operate, there are two power states: on and off. during each state, there is a current loop made by the power components currently conducting. place the power components so that the current loop is conducting in the same direction during each of the two states. this prevents magnetic field reversal caused by the traces between the two half cycles and reduces radiated emi. layout procedure u se the following general guidelines when designing pcbs: ? keep c in close to the vin and gnd leads of the add5205 . ? keep the high current path from c in (through l1) to the sw and gnd leads as short as possible. ? keep the high current path from c in (through l1), d1, and c out as short as possible. ? keep high current traces as short and wide as possible. ? place the c ovp as close as possible to the ovp pin. ? place the led current setting resistors as close as possible to each pin to prevent noise pickup. ? avoid routing noise sensitive traces near high current traces and components, especially the led current setting node (iset). ? use a thermal pad size that is the same dimension as the exposed pad on the bottom of the package. heat sinking when using a surface-mount power ic or external power switches, the pcb can often be used as the heat sink. this is done by using the copper area of the pcb to transfer heat from the device. users should maximize this area to optimize thermal performance.
data sheet add5205 rev. 0 | page 13 of 16 typical application circuit d1 l1 4.7h off on vin shdn add5205 pwm c_filter sw ovp c in 4.7f c filter 1f r set c out 4.7f c ovp 100nf fb1 fb2 fb3 fb4 gnd iset 4 1 3 8 6 2 7 5 12 11 10 9 + ? 09858-015 figure 15. typical application circuit
add5205 data sheet rev. 0 | page 14 of 16 outline dimensions 1.70 1.60 sq 1.50 0.50 0.40 0.30 072809-b 1 0.50 bsc bottom view top view 12 4 6 7 9 10 3 exposed pad p i n 1 i n d i c a t o r 3.10 3.00 sq 2.90 seating plane 0.05 max 0.02 nom 0.20 ref 0.20 min coplanarity 0.08 pin 1 indicator 0.30 0.23 0.18 compliant to jedec standards mo-229-weed-4. for proper connection of the exposed pad, refer to the pin configuration and function descriptions section of this data sheet. 0.80 0.75 0.70 figure 16. 12-lead lead frame chip scale package [lfcsp_wq] 3 mm 3 mm body, very very thin quad (cp-12-6) dimensions shown in millimeters ordering guide model 1 temperature range package description package option ADD5205ACPZ-RL ?25c to +85c 12-lead lead frame chip scale package [lfcsp_wq] cp-12-6 1 z = rohs compliant part.
data sheet add5205 rev. 0 | page 15 of 16 notes
add5205 data sheet rev. 0 | page 16 of 16 notes ?2011 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. d09858-0-8/11(0)

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