? on-bright electronics confidential preliminary datasheet ob_doc_ds_335000 - 1 - OB3350 cost effective led controller general description OB3350 is a highly integrated and cost effective light emitting diode (led) driver optimized for lcd monitor and lcd tv backlighting application. it provides a high performance led backlight solution with minimized bom count. the OB3350 contains a pwm boost driver which uses current mode control and fixed frequency operation to regulate the led current. the led current is sensed through an external current sense resistor. the voltage across the sensing resistor is compared with reference level of 300mv, the error is amplified to control the pulse width of the power switch thus to regulate the current flowing the led. the OB3350 offers external low frequency pwm (lpwm) dimming method for a wide range of dimming control. the OB3350 offers comprehensive protection such as power mosfet over current protection (ocp), output over voltage protection (ovp), ic power supply under voltage lockout (uvlo), and led open protection. features current mode pwm controller with good dynamic response 8v to 35v input voltage range external pwm dimming mode over voltage protection over current protection under voltage lockout (uvlo) thermal shutdown applications lcd monitor lcd tv flat panel display the OB3350 is offered in sop-8 packages. typical application figure1. OB3350 typical application schematic 3350 is offered in sop is offered in sop flat panel display flat panel display is offered in sop free datasheet http://www.datasheetlist.com/
? on-bright electronics confidential preliminary datasheet ob_doc_ds_335000 - 2 - OB3350 cost effective led controller absolute maximum ratings parameter value vin input voltage to gnd -0.3v to 40v i/o to gnd -0.3v to 7v operating ambient temp. t a -40 ~ 85 operating junction temp. t j -40 ~ 150 min/max storage temp. t stg -55 ~150 lead temp. (10 sec) 260 note: stresses beyond those listed under ? absolute maximum ratings ? may cause permanent damage to the device. these are stress ratings only, functional operation of the device at these or any other conditions beyond those indicated under ? recommended operating conditions ? is not implied. exposure to absolute maximum-rated conditions for extended periods may affect device reliability. recommended operating range parameter value vin voltage 8v to 35v burst dimming frequency 100hz to 1khz package thermal characteristics parameter value thermal resistance ja (sop) 150 /w ordering information part number description OB3350cp sop8, pb-free in tube OB3350cpa sop8, pb-free in t&r o b 3 3 5 0 x x x cost effective led controller package package pb- free packing c:sop8 p:pb-free blank:tube a: taping package marking information y : y ear c o d e ww:week code(01-52) zzz:lot code c:sop8 package p:pb-free package s:internal code ( o p tiona l ) package marking information package marking information x x x package package c:sop8 c : sop 8 cpa sop8 description 8, pb-free in tube pb-free in tube pb-free in t free in t 150 / w /w free datasheet http://www.datasheetlist.com/
? on-bright electronics confidential preliminary datasheet ob_doc_ds_335000 - 3 - OB3350 cost effective led controller pin configuration 1 2 3 4 8 7 5 6 pwm comp OB3350 gate ovp fb cs gnd vin no. name i/o pin function 1 vin power power supply input 2 gate i/o gate driver output pin 3 gnd gnd ground 4 cs i/o current sense input 5 fb i/o led current feedback input 6 comp i/o boost converter loop compensation pin 7 ovp i/o over voltage protection sense input 8 pwm i/o external pwm dimming control power supply input gate driver output pin gate driver output pin current sense input current sense input led current feedback input led current feedback input boost converter loop compensation pin boost converter loop compensation pin i /o o pin function power supply input power supply input gate driver output pin gate driver output pin free datasheet http://www.datasheetlist.com/
? on-bright electronics confidential preliminary datasheet ob_doc_ds_335000 - 4 - OB3350 cost effective led controller functional block diagram o v p g a t e v i n c o m p reference c s f b s osc soft-start ea uvlo 5v control logic thermal shutdown pwm comparator sense amplifer ramp adjust vth_ovp pw m gate drive dim control dim p w m g n d figure2. OB3350 functional block diagram o o v p p figure2. OB3350 functional block diagram figure2. OB3350 functional block diagram gate gate drive drive free datasheet http://www.datasheetlist.com/
? on-bright electronics confidential preliminary datasheet ob_doc_ds_335000 - 5 - OB3350 cost effective led controller electrical characteristics vddh=12v,pwm=5v, t a =25 , if not otherwise noted. parameter symbol conditions min typ max u nits current consumption input voltage range 8 - 35 v operating supply current vdd i vin=12v,pwm=5v no load - 2.5 3 ma stand by current stb vdd i _ pwm low >50ms sleep mode - 310 400 ua vdd uvlo uvlo uvlo(on) 6 7 8 v uvlo hysteresis uvlo(hys) 500 mv soft start soft start slope slop sst i _ 400 mv/ms pwm control operating frequency f osc 175 200 225 khz max duty cycle d max 93 95 97 % pwm(high) high level 2.5 v pwm input threshold pwm(low) low level 1.3 v error amplifier reference voltage ea ref v _ reference voltage at non-inverting input 0.289 0.3 0.311 v open loop voltage gain a m 70 db transconductance of ea gm 80 100 120 ua/v output source current source i 24 30 36 ua output sink current k i sin 48 60 72 ua protection threshold ovp v ovp ov threshold of output over voltage 1.8 2.0 2.2 v ocp v th_ocp threshold of over current protection (duty=90%) 330 mv otp on on otp t _ 140 160 180 otp off off otp t _ 120 140 160 connect detect time dio t 1 ms normal operation 200 mv ovp uvlo threshold v ovp uv system startup 100 mv gate driver output gate rise time rise t 500pf load - 40 80 ns gate fall time fall t 500pf load 20 40 ns ocp v ocp v t connect detect time connect detect time ovp uvlo threshold ovp uvlo threshold gate driver output gate rise time gate rise time gate fall time gate fall time 93 95 97 2 2 1 reference voltage at reference voltage at inverting input inverting input gm gm 24 30 36 24 30 36 48 60 72 48 60 72 ovp v ovp v ovp ov ovp ov _ocp 400 400 175 200 225 175 200 225 93 95 97 6 7 8 6 7 8 500 500 400 400 310 400 ua 310 400 ua 6 7 8 v 6 7 8 500 mv free datasheet http://www.datasheetlist.com/
? on-bright electronics confidential preliminary datasheet ob_doc_ds_335000 - 6 - OB3350 cost effective led controller function description general operation the OB3350 is a led driver designed for boost dc-dc converters in a constant frequency mode. the controller implements a peak current mode control scheme and an internal transconductance amplifier to accurately control the output current over a wide input and load conditions. low frequency pwm dimming input that can accept an external control signal with a duty ratio of 1%-100%. OB3350 offers comprehensive protection features to protect the system in various fault conditions such as output over voltage protection, boost diode disconnection protection and output short circuit protection. the cycle-by-cycle current limit function limits the maximum current flowing through the external mosfet. the over temperature protection ensures that the system will not run into condition of thermal runaway and blow up. startup OB3350 is enabled by applying a voltage of greater than approximately 2.5v to pwm pin. an on-chip internal 150k ohm pull down resistor is inserted between pwm pin and ground. when the first rising edge is applied to pwm input, also the pin of pwm is logic high, the OB3350 will power up immediately, and remains power up until the pwm input has been hold low for at least 50ms(typ), at this time the chip will enter sleep mode. at sleep mode, the power of theOB3350 will be lower than 400ua (typ). once OB3350 is enabled the internal 5v regulator will be activated to source a current less than 4ma to the whole chip. when pwm is active high, the OB3350 checks the topology connection first. the chip monitors the ovp pin to see if the schottky diode (boost diode) is connected or the boost output is short to gnd, if the voltage at ovp pin is lower than 100mv, the output will be disabled. the OB3350 will also check other faults (uvlo, ocp and otp), if there is no fault, then the boost converter will boost up the output with the internal soft start. uvlo an under-voltage lockout protection feature with a hysteresis of about 300mv is provided for vddh. when the voltage at this pin exceeds a threshold of approximately 7.5v (typ), the ic starts the normal operation. if the voltage at this pin drops below a threshold of approximately 7(typ) v, the ic stops switching operation. the ic resumes switching operation when the voltage at pin vin increases to a voltage above 7.5v. led current regulation the led current is sensed by current sense resistors connected between pin fb and gnd. the sensed error signal is amplified and compared to the cs pin sensing current signal plus the slope compensation to determine the on-time of the switching mosfet. the error amplifier sources or sinks the current to the comp pin to adjust the required inductor current as the load changes. the slope-compensation signal is added to the current-sense signal to improve the stability at high duty cycles. the average led current is approximated by the following equation ] [ ] [ 300 ] [ fb led r mv ma i at light loading, the OB3350 automatically skips some pulses to improve efficiency and prevent overcharging the output capacitor. in this pulse-skipping mode, the inductor current ramps up for a minimum on-time (typical 300ns), then deliver the stored energy to the output. the switch remains off until another pulse is needed to boost the output voltage. slope compensation the OB3350 uses a current mode control scheme. the main advantages of current mode control are inherent cycle-by-cycle current limit for the switch and simpler control loop characteristics. however, current mode control has an inherent instability for duty cycles greater than 50%, which is also called sub-harmonic oscillation. the OB3350 has a build-in slope compensation to avoid sub-harmonic oscillation. figure4 sub-harmonic oscillation at duty>50% and compensation slope to avoid sub-harmonic oscillation if the control signal (which applied to the negative input of the pwm comparator) has no slope and 3350 3350 is enabled the internal is enabled the internal will be activated to source a current less than will be activated to source a current less than when pwm is active high, the ob when pwm is active high , the ob topology connection first. the chip monitors the topology connection first . the chip monitors the ovp pin to see if the schottky diode ovp pin to see if the schottky diode is connected or the boost output is short to gnd is connected or the boost output is short to gnd the voltage at ovp pin is lower than the voltage at ovp pin is lower than output will be disabled output will be disabled check other faults check other faults is no fault, then the boost converter will boost up is no fault , the output with the internal soft start the output with the internal soft start uvlo an k ohm pull down resistor is k ohm pull down resistor is when the when the , also the also the will power up will power up and remains power up until the pwm and remains power up until the pwm input has been hold low for at least 50ms(typ), input has been hold low for at least 50 ms ( typ ) this time the chip will enter sleep mode. at sleep this time the chip will enter sleep mode . at sleep will be lower than will be lower than [ [ led led i [ led led at light loading, the ob at light loading , the ob some pulses to improve efficiency and prevent some pulses to improve efficiency and prevent overcharging the output capacitor overcharging the output capacitor pulse-skipping mode pulse - skipping mode up for a minimum on up for a minimum on deliver the stored energy deliver the stored energy remains off until another pulse is needed to boost remains off until another pulse is needed to boost the output voltage the output voltage the average led current is approximated by the the average led current is approximated by the 300 3 0 0 ] sinks the current to the comp pin to adjust the sinks the current to the comp pin to adjust the required inductor current as the load changes required inductor current as the load changes compensation signal is added to the compensation signal is added to the sense signal to improve the stability at high sense signal to improve the stability at high the average led current is approximated by the the average led current is approximated by the to the cs pin sensing current signal plus the slope to the cs pin sensing current signal plus the slope time of the time of the the error amplifier sources or the error amplifier sources or sinks the current to the comp pin to adjust the sinks the current to the comp pin to adjust the required inductor current as the load changes. the required inductor current as the load changes. compensation signal is added to the free datasheet http://www.datasheetlist.com/
? on-bright electronics confidential preliminary datasheet ob_doc_ds_335000 - 7 - OB3350 cost effective led controller the slope which representing inductor current ramp up until the comp signal is reached, then ramp down. if the duty > 50%, any distribution won ? t be converged from duty to duty and thus sub-harmonic oscillation happens. for the equation below: ) ( ) 1 ( n e n e f n i s s s s i to avoid sub-harmonic oscillation happening, just make sure (s f -s e ) / (s n +s e ) smaller than 1. for boost applications, the slopes se, sf and sn can be calculated with the formulas below and a typical value of vsl is 50mv. s sl e f v s l v v r s in out sen f / l v r s in sen n / when se increases then the factor which can determine whether the sub-harmonic oscillation will occur decreases. when the duty cycle is greater than 50% and the inductance becomes less, the factor increases. and for more flexibility slope compensation amplitude can be increased by adding one external resistor, rsl, in the cs path. figure 4 shows the setup. the externally generated slope compensation is then added to the internal slope compensation of the OB3350. when using external slope compensation, the formula for se becomes: s sl s sl e f r i v s ) ( a typical value of i s is 40ua. figure5 adding external slope compensation to OB3350 it ? s good design practice to only add as much slope compensation as needed to avoid sub-harmonic oscillation. additional slope compensation minimized the influence of the sensed current in the control loop. with very large slope compensation the control loop characteristics are similar to a voltage mode regulator which compares the error voltage to a saw tooth waveform rather than the inductor current. dimming control the led brightness is controlled by the pwm signal at pwm pin which has different duty cycle. OB3350 can accept an external pwm signal to pwm pin in the range of 100hz to 1 khz with a swing voltage of 0v to a level greater than 2.5v. ovp protection OB3350 shuts down the output if the output voltage is higher than the predetermined threshold level. in case of led failing, the current of led and the resulted voltage drop on sensing resistor is nearly zero; the converter will run at maximum duty cycle that boosts the output voltage to a very high level. to prevent this happen, the output voltage is monitored through pin ovp and converter is shut down if the output voltage exceeds the predetermined level. this protection is latched and OB3350 can be reset from vin or pwm. vout short protection vout short condition is monitored by the voltage at pins ovp. during normal operation, when the voltage at ovp pin drops below a threshold of approximately 0.2v, the vout-short protection function is activated and the gate is turned off. this state is latched and can be reset from vin or pwm. thermal shutdown the OB3350 includes a thermal protection circuit. when the junction temperature exceeds 160 c (typical), the controller and current sources shut down and do not restart until the junction temperature drops below 140 c (typical). figure5 adding external slope compensation to ob figure 5 adding external slope compensation to ob it ? s good design practice to only add as much it ? s good design practice to only add as much slope compensation as needed to avoid generated slope compensation is then added to generated slope compensation is then added to 3350. 3350 . when using external slope compensation, the , the exceeds the predetermined level exceeds the predetermined level is latched and OB3350 is latched and ob 3350 vout short protection vout short protection vout short condition is monitored by the voltage vout short condition is monitored by the voltage at pins ovp. at pins ovp . voltage at ovp pin drops below a threshold of voltage at ovp pin drops below a threshold of approximately approximately function is activated and the gate is turned off function is activated and the gate is turned off this state is latched and can be reset from vin or this state is latched and can be reset from vin or pwm duty cycle that boosts the output voltage to a very to prevent this happen to prevent this happen voltage is monitored through pin ovp and voltage is monitored through pin ovp and converter is shut dow n if the output voltage n if the output voltage exceeds the predetermined level exceeds the predetermined level can be reset from vin or the current of led the current of led and the resulted voltage drop on sensing resistor and the resulted voltage drop on sensing resistor the converter will run at maximum the converter will run at maximum duty cycle that boosts the output voltage to a very duty cycle that boosts the output voltage to a very to prevent this happen, the output , the output shuts down the output if the output shuts down the output if the output voltage is higher than the predetermined threshold voltage is higher than the predetermined threshold the current of led the current of led and the resulted voltage drop on sensing resistor and the resulted voltage drop on sensing resistor the converter will run at maximum free datasheet http://www.datasheetlist.com/
? on-bright electronics confidential preliminary datasheet ob_doc_ds_335000 - 8 - OB3350 cost effective led controller reference application figure6. OB3350 for external lpwm dimming reference application schematic free datasheet http://www.datasheetlist.com/
? on-bright electronics confidential preliminary datasheet ob_doc_ds_335000 - 9 - OB3350 cost effective led controller package mechanical data dimensions in millimeters dimensions in inches symbol min max min max a 1.350 1.750 0.053 0.069 a1 0.050 0.250 0.002 0.010 a2 1.250 1.650 0.049 0.065 b 0.310 0.510 0.012 0.020 c 0.100 0.250 0.004 0.010 d 4.700 5.150 0.185 0.203 e 3.800 4.000 0.150 0.157 e1 5.800 6.200 0.228 0.244 e 1.270 (bsc) 0.050 (bsc) l 0.400 1.270 0.016 0.050 0 o 8 o 0 o 8 o e dimensions in millimeters min a 1.350 1 a 1 . 350 1 1 0.050 0 1 0 050 0 2 1 2 1 b c c d d e e e1 5 e free datasheet http://www.datasheetlist.com/
? on-bright electronics confidential preliminary datasheet ob_doc_ds_335000 - 10 - OB3350 cost effective led controller important notice right to make changes on-bright electronics corp. reserves the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. warranty information on-bright electronics corp. warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with its standard warranty. testing and other quality control techniques are used to the extent it deems necessary to support this warranty. except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. on-bright electronics corp. assumes no liability for applications assistance or customer product design. customers are responsible for their products and applications using on-bright ? s components, data sheet and application notes. to minimize the risks associated with customer products and applications, customers should provide adequate design and operating safeguards. life support on-bright electronics corp. ? s products are not design ed to be used as components in devices intended to support or sustain human life. on-bright electronics corp. will not be held liable for any damages or claims resulting from the use of its products in medical applications. military on-bright electronics corp. ? s products are not designed for use in military applications. on-bright electronics corp. will not be held liable for any damages or claims resulting from the use of its products in military applications. will not be held liable for any damages or ed to be used as components in devices intended to will not be held liable for any damages or claims will not be held liable for any damages or claims on-bright electronics corp. ? s products are not designed for use in military applications. on-bright on-bright electronics corp. ? s products are not designed for use in military applications. on-bright claims resulting from t claims resulting from t ciated with customer products and applications ed to be used as components in devices intended to ed to be used as components in devices intended to will not be held liable for any damages or claims will not be held liable for any damages or claims of each product is not necessarily performed of each product is not necessarily performed ance or customer product design ance or customer product design products and applications using on-bright ? s components, data sheet products and applications using on-bright ? s components, data sheet ciated with customer products and applications ciated with customer products and applications he specifications applicable he specifications applicable testing and other quality control techniques testing and other quality control techniques except where mandated by except where mandated by of each product is not necessarily performed. of each product is not necessarily performed . ance or customer product design ance or customer product design free datasheet http://www.datasheetlist.com/
|
