OB3350CPA

OB3350 Cost Effective LED Controller FEATURES 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. 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 SOP-8 Packages. 3350 is offered in SOP TYPICAL APPLICATION Figure1. OB3350 Typical Application Schematic ©On-Bright Electronics Confidential -1- Preliminary datasheet OB_DOC_DS_335000 OB3350 Cost Effective LED Controller Recommended Operating Range 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. TA -40 ~ 85 Operating Junction Temp. TJ -40 ~ 150 Min/Max Storage Temp. Tstg -55 ~150 Lead Temp. (10 Sec) 260 Note: Stresses beyond those listed under “absolute maximum Parameter Vin Voltage Burst Dimming Frequency Value 8V to 35V 100Hz to 1KHz Package Thermal Characteristics Parameter Thermal Resistance JA (SOP) Value 150 /W ratings” may cause permanent damage to the device. These Ordering Information are stress ratings only, functional operation of the device at these or any other conditions beyond those indicated under Part Number OB3350CP OB3350CPA CPA “recommended operating conditions” is not implied. Exposure to absolute maximum-rated conditions for extended periods Description SOP8, 8, pb-free in tube SOP8, SOP8 pb-free free in T T&R may affect device reliability. OB3350 X X Package X Package Pb- free Cost Effective LED Controller C:SOP8 P:Pb-free Packing Blank:Tube A: Taping Package Marking Information Y:Year Code WW:Week Code(01-52) ZZZ:Lot Code C:SOP8 Package P:Pb-free Package S:Internal Code(Optional) ©On-Bright Electronics Confidential -2- Preliminary datasheet OB_DOC_DS_335000 OB3350 Cost Effective LED Controller Pin Configuration VIN 1 8 PWM GATE 2 7 OVP GND 3 6 COMP CS 4 5 FB OB3350 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 O External PWM Dimming Control ©On-Bright Electronics Confidential -3- Preliminary datasheet OB_DOC_DS_335000 OB3350 Cost Effective LED Controller Functional Block Diagram UVLO DIM OSC VIN Ramp Adjust 5V Thermal Shutdown Reference Soft-start PW M S COMP Control Logic Gate Drive GATE PWM Comparator EA FB Vth_ovp DIM Control PWM Sense Amplifer GND CS OVP O VP P Figure2. OB3350 Functional Block Diagram ©On-Bright Electronics Confidential -4- Preliminary datasheet OB_DOC_DS_335000 OB3350 Cost Effective LED Controller Electrical Characteristics VDDH=12V,PWM=5V, TA=25 Parameter Current Consumption Input voltage range , if not otherwise noted. Symbol Conditions Vin=12V,PWM=5V no load PWM low >50ms sleep mode Operating supply current IVDD Stand by current IVDD _ STB VDD UVLO UVLO UVLO Hysteresis Soft start UVLO(ON) UVLO(Hys) Soft start slope I sst _ slop PWM Control Operating frequency Max duty cycle PWM Input Threshold Min Typ Max Units 8 - 35 V - 2.5 3 mA - 310 400 uA 6 7 500 8 V mV 400 FOSC Dmax PWM(high) PWM(low) 175 93 High Level Low Level Vref _ ea Reference voltage at inverting input non-inverting mV/mS 200 95 225 97 2.5 2 KHz % V V 0.289 0.3 0.311 V 80 70 100 120 dB uA/V 1 1.3 Error Amplifier Reference voltage Open loop voltage gain Transconductance of EA Am Gm Output source current I source 24 30 36 uA Output sink current I sin k 48 60 72 uA 1.8 2.0 2.2 V Protection Threshold Threshold of output over voltage Threshold of over current protection (duty=90%) OVP VOVP OV OCP Vth_OCP _OCP OTP ON TOTP _ ON 140 160 180 OTP OFF TOTP _ OFF 120 140 160 Connect detect time Tdio OVP UVLO threshold VOVP UV 330 Normal operation System startup mV 1 mS 200 100 mV mV Gate Driver Output Gate rise time Trise 500pF load Gate fall time T fall 500pF load ©On-Bright Electronics Confidential -5- - 40 80 ns 20 40 ns Preliminary datasheet OB_DOC_DS_335000 OB3350 Cost Effective LED Controller Function Description switching operation when the voltage at pin VIN increases to a voltage above 7.5V. General Operation LED Current Regulation 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. 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 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. changes The slope-compensation compensation signal is added to the current-sense sense signal to improve the stability at high duty cycles. The average LED current is approximated by the following equation 300[ mV ] I LED [mA] R FB [ ] At light loading, the OB OB3350 automatically skips some pulses to improve efficiency and prevent overcharging the output capacitor capacitor. In this pulse-skipping mode mode, the inductor current ramps up for a minimum on 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 voltage. Startup OB3350 is enabled by applying a voltage of greater than approximately 2.5V to PWM pin. An on-chip internal 150kk 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) 50ms(typ), at this time the chip will enter sleep mode. At sleep mode, the power of theOB3350 3350 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 OB 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 GND, if the voltage at OVP pin is lower than 100mV, the output will be disabled. 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 start. 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. 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 ©On-Bright Electronics 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 Confidential -6- Preliminary datasheet OB_DOC_DS_335000 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: S f Se I ( n 1) I ( n) Sn Se To avoid sub-harmonic oscillation happening, just make sure (Sf-Se) / (Sn+Se) 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 e VSL f s Sf R sen Vout 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, happen, the output voltage is monitored through Pin OVP and converter is shut down n if the output voltage exceeds the predetermined level. level This protection is latched and OB3350 can be reset from VIN or PWM. Vin / L S n R sen Vin / L 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 3350. the internal slope compensation of the OB3350. When using external slope compensation,, the formula for Se becomes: S e (VSL I s RSL ) f s A typical value of Is is 40uA. 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. off This state is latched and can be reset from VIN or PWM. 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 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. ©On-Bright Electronics Confidential -7- Preliminary datasheet OB_DOC_DS_335000 OB3350 Cost Effective LED Controller Reference Application Figure6. OB3350 for external LPWM dimming Reference Application Schematic ©On-Bright Electronics Confidential -8- Preliminary datasheet OB_DOC_DS_335000 OB3350 Cost Effective LED Controller PACKAGE MECHANICAL DATA Symbol A A1 1 A2 2 b c D E E1 E e L ©On-Bright Electronics Dimensions In Millimeters Min Max 1.350 1.750 1 0.050 0 050 0 0.250 1 1.250 1.650 0.310 0.510 0.100 0.250 4.700 5.150 3.800 4.000 5.800 5 6.200 1.270 (BSC) 0.400 1.270 0º 8º Confidential -9- Dimensions In Inches Min Max 0.053 0.069 0.002 0.010 0.049 0.065 0.012 0.020 0.004 0.010 0.185 0.203 0.150 0.157 0.228 0.244 0.050 (BSC) 0.016 0.050 0º 8º Preliminary datasheet OB_DOC_DS_335000 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 he 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. performed On-Bright Electronics Corp. assumes no liability for applications assistance design. ance 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 ciated with customer products and applications, applications customers should provide adequate design and operating safeguards. Life support On-Bright Electronics Corp.’s products are not designed 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 tthe use of its products in military applications. ©On-Bright Electronics Confidential - 10 - Preliminary datasheet OB_DOC_DS_335000