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| mp3397 step-up, 4-string max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 1 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. the future of analog ic technology description the mp3397 is a step-up controller with 4 current channels designed to drive wled arrays for large-size lcd-panel backlighting applications. the mp3397 is flexible, and can expand the number of led channels with two or more mp3397s in parallel operating from a single inductive power source. the mp3397 uses current-mode fixed- frequency architecture. an external resistor sets the switching frequency. this signal drives an external mosfet to boost up the output voltage from 5v to a 28v input supply. the mp3397 regulates the current in each led string to the programmed value set by an external current-setting resistor. the mp3397 applies 4 internal current sources for current balance. the current matching can achieve 2.5% regulation accuracy between strings. its low regulation voltage on led current sources reduces power loss and improves efficiency. an external pwm input signal or dc input signal controls pwm dimming. the dimming pwm signal can be generated internally and the dimming frequency is programmed by an external setting capacitor. features ? 4-string, max 350ma/string at 10% d pwm ? 5v to 28v input voltage range ? 2.5% current matching accuracy between strings ? programmable switching frequency ? pwm or dc input burst pwm dimming ? open and short led protection ? programmable over-voltage protection ? cascading capability with a single power source ? under-voltage lockout ? thermal shutdown ? 16-pin tssop soic package applications ? desktop lcd flat panel displays ? flat panel video displays ? 2d/3d lcd tvs and monitors a ll mps parts are lead-free and adhere to the rohs directive. for mps green status, please visit mps website under quality assurance. ?mps? and ?the future of analog ic technology? are registered trademarks of monolithi c power systems, inc.
mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 2 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical application mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 3 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. ordering information part number package top marking mp3397ef * tssop16 mp3397 MP3397ES** soic16 mp3397 * for tape & reel, add suffix ?z (eg. mp3397ef?z). for rohs compliant packaging, add suffix ?lf (eg. mp3397ef?lf?z) ** for tape & reel, add suffix ?z (eg. MP3397ES?z). for rohs compliant packaging, add suffix ?lf (eg. MP3397ES?lf?z) package reference tssop16 soic16 absolute maxi mum ratings (1) vin ................................................ -0.3v to +30v v gate ............................................ -0.5v to +6.8v vcc ............................................. -0.5v to +6.8v v led1 to v led4 .................................... -1v to +55v all other pins ............................... -0.3v to +6.3v continuous power dissipation (t a = 25c) (2) tssop16 ................................................ 2.78 w soic16 ................................................... 1.56 w junction temperature ............................... 150c lead temperature .................................... 260c storage temperature .............. -65 c to +150c recommended operating conditions (3) supply voltage vin ............................. 5v to 28v led current (backlight) ........... 10ma to 350ma operating junction temp. (t j ). -40c to +125c thermal resistance (4) ja jc tssop16 ................................ 45 ...... 10 ... c/w soic16 ................................... 80 ...... 35 ... c/w notes: 1) exceeding these ratings may damage the device. 2) the maximum allowable power dissipation is a function of the maximum junction temperature t j (max), the junction-to- ambient thermal resistance ja , and the ambient temperature t a . the maximum allowable continuous power dissipation at any ambient temperature is calculated by p d (max) = (t j (max)-t a )/ ja . exceeding the maximum allowable powe r dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. internal thermal shutdown circuitry protects the device from permanent damage. 3) the device is not guaranteed to function outside of its operation conditions. 4) measured on jesd51-7, 4-layer pcb. mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 4 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. electrical characteristics v in =12v, v en = 5v, t a = 25c, unless otherwise noted. parameters symbol condition min typ max units operating input voltage v in 5 28 v supply current (quiescent) i q v in =12v, v en =5v, no load with switching 4 ma supply current (shutdown) i st v en =0v, v in =12v 2 a ldo output voltage v cc v en =5v, 7v mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 6 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. pin functions pin # name description 1 comp step-up converter compensation pin. this pi n compensates the regulation control loop. connect a ceramic capacitor from comp to gnd. 2 en enable control input. turn-on threshold at 1.8v. turn-off threshold at 0.6 v. do not let this pin float. 3 dbrt brightness control input. apply a pwm signal on this pin for for external pwm dimming mode. apply a dc voltage range from 0.2v to 1.2v on this pin to linearly set the internal dimming duty cycle from 0% to 100% for dc-input pwm dimming mode. the mp3397 has positive dimming polarity on dbrt. 4 gnd ground. 5 osc switching frequency set. connect a resistor between osc and gnd to set the step-up converter switching frequency. the voltage at this pin is regulated to 1.23v. the clock frequency is proportional to the current sourced from this pin. 6 iset led current set. tie a current-setting resistor from this pin to ground to program the current in each led string. this pin voltage is regulated to 1.23v. the led current is proportional to the current through the iset resistor. 7 bosc dimming repetition set. this is the timing pin for the oscillator to set the dimming frequency. to use dc input pwm dimming mode , connect a capacitor from this pin to gnd to set the internal dimming frequency. a saw-tooth waveform is generated on this pin. to use external pwm dimming mode, connect a resistor from this pin to gnd, and apply the pwm signal on dbrt pin. 8 led4 led string 4 current input. this pin is the open-drain output of an internal dimming control switch. connect the led string 4 cathode to this pin. 9 led3 led string 3 current input. this pin is the open-drain output of an internal dimming control switch. connect the led string 3 cathode to this pin. 10 led2 led string 2 current input. this pin is the open-drain output of an internal dimming control switch. connect the led string 2 cathode to this pin. 11 led1 led string 1 current input. this pin is the open-drain output of an internal dimming control switch. connect the led string 1 cathode to this pin. 12 ovp over-voltage protection input. connect a resi stor divider from output to this pin to program the ovp threshold. when this pin voltage reaches 1.23v, the mp3397 triggers over voltage protection mode. 13 isense current sense input. during normal operation, this pin senses the voltage across the external-inductor current-sensing resistor (r sense ) for peak-current?mode control and also to limit the inductor current during every sw itching cycle. if this pin is not used for cascading applications, tie this pin to gnd; do not let this pin float. 14 gate step-up converter power switch gate output. this pin drives the external power n-mos device. 15 vin supply input. vin supplies the power to the chip , as well as the step-up converter switch. drive vin with a 5v to 28v power source. must be locally bypassed. 16 vcc the internal 6v linear regulator output. v cc provides power supply for the external mosfet switch gate driver and the internal co ntrol circuitry. bypass vcc to gnd with a ceramic capacitor. mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 7 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performanc e characteristics v in =12v, 10 leds in series, 4 strings in parallel, 220ma/string, unless otherwise noted. v sw 20v/div. v comp 1v/div. v out 20v/div. i led 2a/div. steady state v sw 20v/div. v out 20v/div. v in 10v/div. i led 500ma/div. vin startup v sw 20v/div. v out 20v/div. v en 5v/div. i led 500ma/div. ven startup v sw 20v/div. v bosc 1v/div. v out 20v/div. i led 1a/div. dc burst dimming v pwm = 0.9v, c bosc = 2.2nf v sw 20v/div. v out 20v/div. v pwm 5v/div. i led 1a/div. external pwm dimming f pwm = 200hz, d pwm = 50% v sw 20v/div. v out 20v/div. i led 1a/div. open led protection open all led strings at working v sw 20v/div. v out 20v/div. i led 1a/div. open led protection open one led string at working v sw 20v/div. v out 20v/div. v led1 20v/div. i led 1a/div. short led protection short a string at working efficiency efficiency vs. vin input voltage (v) 80.0% 82.0% 84.0% 86.0% 88.0% 90.0% 92.0% 94.0% 96.0% 98.0% 100.0% 10 12 14 16 18 20 22 24 26 mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 8 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. functional block diagram control logic + - current sense amplifier + - pwm comparator oscillator + - 1.23v ov comparator + - + - led1 + - dpwm oscillator dpwm comparator + - 1.23v feedback control 6.3v ea led ov comparator short string protection regulator led4 ovp isense gnd vin vcc dbrt bosc iset comp osc en enable control ref gate current control figure 1?mp3397 functional block diagram mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 9 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. operation the mp3397 employs a programmable constant- frequency, peak-current?mode step-up converter with 4 channels or regulated current sources to drive an array of up to 4 strings of white leds. internal 6v regulator the mp3397 includes an internal linear regulator (vcc). when vin is greater than 6.5v, this regulator outputs a 6v power supply to the external mosfet switch gate driver and the internal control circuitry. the vcc voltage drops to 0v when the chip shuts down. the mp3397 features under-voltage lockout (uvlo). the chip is disabled until vcc exceeds the uvlo threshold. the uvlo hysteresis is approximately 200mv. system startup when enabled, the mp3397 checks the topology connection first. the chip monitors the over- voltage protection (ovp) pin to see if the schottky diode is not connected or if the boost output is shorted to gnd. an ovp voltage of less than 70mv will disable the chip. the mp3397 also checks other safety limits, including uvlo and over-temperature protection (otp) after passing the ovp test. if all the protection tests pass, the chip then starts boosting the step-up converter with an internal soft-start. the enable signal must occur after the establishment of the input voltage and pwm dimming signal during the start-up sequence. step-up converter the converter operating frequency is programmable (from 150khz to 500khz) with an external set resistor on the osc pin. this flexibility helps to optimize the size of external components and improve the efficiency. at the beginning of each cycle, the internal clock turns on the external mosfet. a stabilizing ramp added to the output of the current sense amplifier prevents sub-har monic oscillations for duty cycles greater than 50 percent. this result is fed into the pwm comparator. when this resulting voltage rises to the level of the error amplifier output voltage (v comp ), the external mosfet turns off. the output voltage of the internal error amplifier is an amplified signal of the difference between the reference voltage and the feedback voltage. the converter automatically chooses the lowest active ledx pin voltage to provide a high- enough bus voltage to power all the led arrays. if the feedback voltage drops below the reference, the output of the error amplifier increases. this result in more current flowing through the mosfet, thus increasing the power delivered to the output. this forms a closed loop that regulates the output voltage. under light-load operation?where v out vin? the converter runs in pulse-skipping mode where the mosfet turns on for a minimum on-time of approximately 100ns, and then the converter discharges the power to the output for the remaining period. the external mosfet remains off until the output voltage needs to be boosted again. dimming control the mp3397 provides two pwm dimming methods: external pwm signal or dc-input pwm dimming mode (see figure 2). + - dpwm oscillator dpwm comparator dbrt bosc ex-pwm input c bosc dpwm output figure 2?pwm dimming method mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 10 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. for external pwm dimming, ground the bosc pin through a resistor, and apply an external pwm signal to the dbrt pin. for dc-input pwm dimming, apply a dc analog signal to the dbrt pin, and connect a capacitor from bosc to ground. the dc signal is then converted to a dpwm dimming signal with a proportional oscillation frequency. the brightness of the led array is proportional to the duty cycle of the dpwm signal. the dpwm signal frequency is set by the capacitor from the bosc pin to ground. open string protection open string protection is achieved through the ovp pin and the led (1 to 4) pins. if one or more strings are open, the respective ledx pins are pulled to ground and the ic keeps charging the output voltage until it reaches the over-voltage protection (ovp) threshold. then the chip marks which strings have an ledx pin voltage lower than 196mv. once marked, the remaining led strings force the output voltage back into tight regulation. the string with the largest voltage drop determines the output regulation. the mp3397 will always attempt to light at least one string. if all strings are open, the mp3397 shuts down the step-up converter. the strings will remain in this marked state until the chip reset. short string protection the mp3397 monitors the ledx pin voltages to determine if a short string fault has occurred. if one or more strings are shorted, the corresponding ledx pins tolerate this higher voltage. if an ledx pin voltage is higher than 6.3v, this condition triggers the detection of a short string. when a short string fault (ledx over-voltage fault) continues for 4096 switching cycles, the fault string is marked off and disabled. once a string is marked off, it disconnects from the output voltage loop. the marked led strings shut off completely until the part restarts. if all strings are shorted, the mp3397 will shut down the step-up converter. the strings remain marked off until the chip resets. mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 11 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. application information selecting the switching frequency set the switching frequency of the step-up converter from 150khz to 500khz for most applications. an oscillator resistor on osc pin sets the internal oscillator frequency for the step- up converter according to the equation: sw osc 62100 f(khz) r(k) ? ? for r osc =330k ? , the switching frequency is set to 188khz. setting the led current the led string currents are identical and set through the current setting resistor on the iset pin. led set 790 1.23v i(ma) (r +0.4)k ? ? ? for r set =7.68k ? , the led current is set to 120ma. the iset pin can not be open. selecting the input capacitor the input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. the input capacitor impedance at the switching frequency should be less than the input source impedance to prevent the high-frequency switching current from passing through to the input. use ceramic capacitors with x5r or x7r dielectrics for their low esr and small temperature coefficients. for most applications, use a 4.7 f ceramic capacitor in parallel with a 220f electrolytic capacitor. selecting the inductor and current sensing resistor the mp3397 requires an inductor to supply a higher output voltage while being driven by the input voltage. a larger value inductor results in less ripple current, resulting in lower peak inductor current and reducing stress on the internal n-channel mosfet. however, larger- value inductors have a larger physical size, higher series resistance, and lower saturation current. choose an inductor that does not saturate under the worst-case load conditions. select the minimum inductor value to ensure that the boost converter works in continuous conduction mode with high efficiency and good emi performance. calculate the required inductance value using the equation: 2 out sw load v d(1d) l 2 f i ???? ? ?? out in v v 1 d ? ? where v in and v out are the input and output voltages, f sw is the switching frequency, i load is the led load current, and is the efficiency. the switching current is usually used for the peak current mode control. in order to avoid hitting the current limit, the voltage across the sensing resistor r sense must measure less than 80% of the worst-case current-limit voltage, v sense . sense sense l(peak) 0.8 v r i ? ? out load in out in l(peak) in sw out vi v(v-v) i v 2lfv ?? ?? ?? ? where i l(peak) is the peak value of the inductor current. v sense is shown in figure 3. current limit-vsense (mv) duty cycle (%) vsense vs. duty cycle 0 100 200 300 400 500 0 102030405060708090100 figure 3?v sense vs duty cycle selecting the power mosfet the mp3397 is capable of driving a wide variety of n-channel power mosfets. the critical parameters of selection of a mosfet are: 1. maximum drain-to-source voltage, vds(max) 2. maximum current, id(max) 3. on-resistance, rds(on) 4. gate source charge qgs and gate drain charge qgd mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 12 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. 5. total gate charge, qg ideally, the off-state voltage across the mosfet is equal to the output voltage. considering the voltage spike when it turns off, v ds(max) should be greater than 1.5 times of the output voltage. the maximum current through the power mosfet occurs at the maximum input voltage and the maximum output power. the maximum rms current through the mosfet is given by rms(max) in(max) max iid ?? , where: out in(min) max out vv d v ? ? the current rating of the mosfet should be greater than 1.5xi rms the on resistance of the mosfet determines the conduction loss, which is given by: k r i p (on) ds 2 rms cond ? ? ? where k is the temperature coefficient of the mosfet. the switching loss is related to q gd and q gs1 which determine the commutation time. q gs1 is the charge between the threshold voltage and the plateau voltage when a driver charges the gate, which can be read in the chart of v gs vs. q g of the mosfet datasheet. q gd is the charge during the plateau voltage. these two parameters are needed to estimate the turn-on and turn-off losses. sw in ds plt dr g gd sw in ds th dr g gs1 sw f i v v v r q f i v v v r q p ? ? ? ? ? ? ? ? ? ? ? ? where v th is the threshold voltage, v plt is the plateau voltage, r g is the gate resistance, and v ds is the drain-source voltage. please note that calculating the switching loss is the most difficult part in the loss estimation. the formula above provides a simplified equation. for more accurate estimates, the equation becomes much more complex. the total gate charge, q g , is used to calculate the gate drive loss. the expression is sw dr g dr f v q p ? ? ? where v dr is the drive voltage. selecting the output capacitor the output capacitor keeps the output voltage ripple small and ensures feedback loop stability. the output capacitor impedance must be low at the switching frequency. ceramic capacitors with x7r dielectrics are recommended for their low esr characteristics. for most applications, a 4.7 f ceramic capacitor in parallel with a 22 f electrolytic capacitor will suffice. setting the over voltage protection the open string protection is achieved through the detection of the voltage on the ovp pin. in some cases, an led string failure results in the feedback voltage always zero. the part then keeps boosting the output voltage higher and higher. if the output voltage reaches the programmed ovp threshold, ovp will trigger. to ensure the chip functions properly, select the resistor values for the ovp resistor divider to provide an appropriate set voltage. the recommended ovp point is about 1.1 to 1.2 times higher than the output voltage for normal operation. high ovp low r v1.23(1 ) r ??? selecting dimming control mode the mp3397 provides two different dimming methods 1. direct pwm dimming an external pwm dimming signal is employed to achieve pwm dimming control. connect a 100k ? resistor from bosc pin to gnd and apply a pwm dimming signal?in the range of 100hz to 20khz?to the dbrt pin. the minimum recommended amplitude of the pwm signal is 1.2v. the low level should be less than 0.4v (see figure 4). mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 13 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. figure 4?direct pwm dimming table 1 shows the pwm dimming duty range with different pwm dimming frequency. tab 1 the range of pwm dimming duty f pwm (hz) d min d max 100 mp3397?4-string, max 350ma/string white led driver mp3397 rev. 1.01 www.monolithicpower.com 15 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. package information tssop16 with external thermal pad mp3397?4-string, max 350ma/string white led driver notice: the information in this document is subject to change wi thout notice. users should warra nt and guarantee that third party intellectual property rights are not infringed upon w hen integrating mps products into any application. mps will not assume any legal responsibility for any said applications. mp3397 rev. 1.01 www.monolithicpower.com 16 9/4/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. package information soic16 0.016(0.41) 0.050(1.27) 0 o -8 o detail "a" 0.010(0.25) 0.020(0.50) x 45 o see detail "a" 0.0075(0.19) 0.0098(0.25) 0.150 (3.80) 0.157 (4.00) pin 1 id 0.050(1.27) bsc 0.013(0.33) 0.020(0.51) seating plane 0.004(0.10) 0.010(0.25) 0.386( 9.80) 0.394(10.00) 0.053(1.35) 0.069(1.75) top view front view 0.228 (5.80) 0.244 (6.20) side view 1 8 16 9 recommended land pattern 0.213 (5.40) 0.063 (1.60) 0.050(1.27) 0.024(0.61) note: 1) control dimension is in inches. dimension in bracket is in millimeters. 2) package length does not include mold flash, protrusions or gate burrs. 3) package width does not include interlead flash or protrusions. 4) lead coplanarity (bottom of leads after forming) shall be 0.004" inches max. 5) drawing conforms to jedec ms-012, variation ac. 6) drawing is not to scale. 0.010(0.25) bsc gauge plane |
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