OB3353ACPA

OB3353A High performance and Cost Effective LED Controller GENERAL DESCRIPTION FEATURES OB3353A 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 OB3353A 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 400mV, the error is amplified to control the pulse width of the power switch thus to regulate the current flowing the LED. The OB3353A offers PWM to analog dimming method for a wide range of dimming control. The OB3353A offers comprehensive protection such as power MOSFET over current protection (OCP), output over voltage protection (OVP), Diode & Inductor short protection, LED cathode short to GND protection, IC power supply under voltage lockout (UVLO), and LED open protection.  丰 鼎         Current Mode PWM Controller With Good Dynamic Response 9V to 30V Input Voltage Range PWM to analog Dimming Mode Over Voltage Protection Over Current Protection Under Voltage Lockout (UVLO) Thermal Shutdown Diode & Inductor Short Protection LED cathode short to GND Protection o LCD Monitor LCD TV Flat panel display en tia lt    新 APPLICATIONS on fid The OB3353A is offered in SOP-8/ CPC8 Packages. TYPICALICAL APPLICATION ENA ht c VIN nB rig 1 PWM 2 3 4 OVP VIN GATE GND CS PWM OVP CMP FB 8 7 OVP 6 5 OB3353A O GND Figure1. OB3353A Typical Application Schematic ©On-Bright Electronics Confidential -1- Datasheet OB_DOC_DS_3353AA2 OB3353A High performance and Cost Effective LED Controller Absolute Maximum Ratings Recommended Operating Range Parameter VIN, GATE，OVP to GND 2 2 2 2/3 CS , FB , COMP, PWM to GND Operating Ambient Temp. TA Operating Junction Temp. TJ Min/Max Storage Temp. Tstg Lead Temp. (10 Sec) Parameter VIN Voltage PWM Frequency for analog Dimming Value -0.3V to 33V -0.3V to 7V -40℃ ~ 85℃ -40℃~ 150℃ -55℃ ~150℃ 260℃ Ordering Information o OB3353ACPA en tia lt OB3353AKFP on fid X X -free in -free in -free in P:Halogen-free Packing Blank:Tube A: Taping ht c C:SOP8 KF:CPC8 -free in X Package Halogen- free Package 丰 Description SOP8, Halogen tube SOP8, Halogen T&R CPC8, Halogen tube CPC8, Halogen T&R 新 Part Number OB3353ACP Value 150℃/W 190℃/W 鼎 Parameter Thermal Resistance θJA (SOP) Thermal Resistance θJA (CPC) OB3353AKFPA High performance and Cost Effective LED Controller 5KHz to 50KHz Package Thermal Characteristics Note1: 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. Note2: Rating value refers to DC only. For small duty cycle pulse in less than 500ns in one period (typical 8.33uS), negative spike value is relaxed to -2V. Note3: Rating value refers to DC only. For small duty cycle pulse in less than 100ns in one period (typical 8.33us), negative spike value is relaxed to -5V. OB3353A Value 9V to 30V rig Marking Information O nB YWWZZZ OB3353CP A S Y:Year Code WW:Week Code(01-52) ZZZ:Lot Code C:SOP8 Package P:Halogen-free Package A:Character Code S:Internal Code(Optional) ©On-Bright Electronics 353YWW . ZZZA s Y:Year Code WW:Week Code(01-52) ZZZ:Lot Code A:Character Code S:Internal Code(Optional) Confidential -2- Datasheet OB_DOC_DS_3353AA2 OB3353A High performance and Cost Effective LED Controller Pin Configuration 1 GATE 2 OB3353A 8 PWM 7 OVP 3 6 COMP CS 4 5 FB 丰 GND 鼎 VIN Name I/O Pin Function 1 VIN Power Power Supply Input 2 GATE Output Gate Driver Output Pin 3 GND Power Ground 4 CS I/O 5 FB Input 6 COMP I/O 7 OVP Input Over Voltage Protection Sense Input 8 PWM Input PWM signal input pin for analog dimming control 新 No. o Current Sense Input en tia lt LED Current Feedback Input O nB rig ht c on fid Boost Converter Loop Compensation Pin ©On-Bright Electronics Confidential -3- Datasheet OB_DOC_DS_3353AA2 OB3353A High performance and Cost Effective LED Controller Functional Block Diagram OSC 丰 VIN UVLO PWM control reference PWM L en tia lt COMP Control Logic o Σ 新 鼎 Thermal Shutdown Gate Drive GATE PWM Comparator EA FB OVP Protection Current Sense GND on fid CS OVP O nB rig ht c Figure2. OB3353A Functional Block Diagram ©On-Bright Electronics Confidential -4- Datasheet OB_DOC_DS_3353AA2 OB3353A High performance and Cost Effective LED Controller Electrical Characteristics FOSC Dmax Reference voltage Vref _ ea Open loop voltage gain Transconductance of EA Am Gm Output source current I source Output sink current I sin k VOVP_OV OCP ht c OVP Vth_OCP rig OTP ON 30 V - 2 3 mA - 130 180 uA 7.8 8.3 800 8.8 V mV 110 93 Reference voltage at non-inverting input Threshold of output over voltage Threshold of over current protection (duty=90%) 392 VTH_CS CMP high protection threshold VTH_CMP OVP UVLO threshold VOVP UV 丰 - 130 97 KHz % 400 408 mV 70 100 dB uA/V 30 uA 60 uA - 1.9 260 100 1.3 % V V 2.0 2.1 V 380 500 mV 160 Diode or Inductor short FB short to GND Normal operation System startup mV/ms 120 95 0 2.5 TOTP _ ON CS high protection threshold nB 9 22 on fid PWM to Analog Dimming Control PWM duty high PWM Logic input level low Protection Threshold Units 新 PWM Control Operating frequency Max duty cycle Error Amplifier Max o I sst _ slop Typical en tia lt Soft start slope Min 鼎 VIN=12V,PWM=5V, TA=25℃, if not otherwise noted. Parameter Symbol Conditions Current Consumption Input voltage range Vin=12V,PWM=5V IVDD Operating supply current no load PWM low >50ms IVDD _ STB Stand by current sleep mode VDD UVLO UVLO UVLO(OFF) UVLO Hysteresis UVLO(Hys) Soft start ℃ 1.1 1.2 1.3 V 2.9 3.2 250 150 3.5 V mV mV - 40 ns 20 ns Gate Driver Output Trise 1nF load Gate fall time T fall 1nF load O Gate rise time ©On-Bright Electronics Confidential -5- Datasheet OB_DOC_DS_3353AA2 OB3353A High performance and Cost Effective LED Controller OCP vs Duty O nB rig ht c on fid en tia lt o 新 鼎 丰 CHARACTERIZATION PLOTS ©On-Bright Electronics Confidential -6- Datasheet OB_DOC_DS_3353AA2 OB3353A High performance and Cost Effective LED Controller Function Description 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 error amplifier reference is set by internal reference voltage and the PWM duty cycle at PWM pin. The average LED current is approximated by the following equation； 400  DUTY PWM [mV ] I LED [mA]  RFB [] At light loading, the OB3353A automatically skips some pulses to improve efficiency and prevent over charging the output capacitor. In this pulse-skipping mode, the inductor current ramps up for a minimum on-time (typical 600ns), then deliver the stored energy to the output. The switch remains off until another pulse is needed to boost the output voltage. en tia lt o 新 鼎 丰 General Operation The OB3353A 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. The transconductance amplifier reference is set by internal reference voltage and the PWM duty cycle at PWM pin. OB3353A offers comprehensive protection features to protect the system in various fault conditions such as LED open protection, output over voltage protection (OVP), the cathode of LED short to GND protection(CMP high), Diode & Inductor short protection(CS high). 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. ht c on fid Startup OB3353A is enabled by applying a voltage of greater than approximately 2.5V to PWM pin. An on-chip internal 220KΩ pull down resistor is inserted between PWM pin and ground. When the first rising edge is applied to PWM input, the OB3353A will power up immediately, and remains power up until the PWM input is lower than 1.3V for at least 20ms(typical), at this time the chip will enter standby mode. At standby mode, the power of theOB3353A will be lower than 130uA (typical). Once OB3353A 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 OB3353A 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 150mV, the output will be disabled. The OB3353A will also check other faults (UVLO, CS high, CMP high, FB high, OCP and OTP), if there is no fault, then the boost converter will boost up the output with the internal soft start. O nB rig Slope Compensation The OB3353A 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 OB3353A has a build-in slope compensation to avoid sub-harmonic oscillation. Voltage UVLO An under-voltage lockout protection feature with a hysteresis of about 800mv is provided for VIN. When the voltage at this pin exceeds a threshold of approximately 8.3V (typical), the IC starts the normal operation. If the voltage at this pin drops below a threshold of approximately 7.5V (typical), the IC stops switching operation. The IC resumes switching operation when the voltage at pin VIN increases to a voltage above 8.3V (typical). ©On-Bright Electronics Dimming Control The LED brightness is controlled by the PWM signal at PWM pin which has different duty cycle. OB3353A can accept an external PWM signal to PWM pin in the range of 5KHz to 50KHz with a swing voltage of 0V to a level greater than 2.5V. An internal square wave whose duty cycle is the same as the duty cycle of the external PWM signal to PWM pin is filtered to provide reference voltage of EA input which determines the FB reference. Input of PWM Comparator Waveform Se Sf ΔI(n) Sn ΔI(n+1) ΔI(n+2) Vsense time Figure2 Sub-harmonic oscillation at duty>50% compensation slope to avoid sub-harmonic oscillation Confidential -7- and Datasheet OB_DOC_DS_3353AA2 OB3353A High performance and Cost Effective LED Controller If the control signal (which applied to the negative input of the PWM comparator) has no slope and 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 鼎 丰 LED Open Protection OB3353A 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 OB3353A can be reset from VIN or PWM. 新 LED Cathode Short to GND Protection When LED cathode is shorted to GND, the boost converter will continuously increase the output to OVP to shut down gate output. But in some condition, if the output is power limited by OCP protection before the output reach the OVP voltage, the gate can never be turned off, in this case large current will go through both Schottky diode and MOSFET, and cause permanent damage. OB3353A will monitor the voltage on COMP pin, if the voltage on COMP pin is continuously greater than 3.2V (typical) for 37ms (typical). The gate output will be latched off for the safe propose. o S f  Rsen  Vout  Vin  / L ht c on fid en tia lt S n  Rsen  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 3 shows the setup. The externally generated slope compensation is then added to the internal slope compensation of the OB3353A. When using external slope compensation, the formula for Se becomes: S e  (VSL  I s  RSL )  f s A typical value of Is is 50uA. GATE OB3353A RSL 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 0.25V (typical), 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. RSen nB rig CS Figure3. Adding external slope compensation to OB3353A 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. Thermal Shut Down The OB3353A includes a thermal protection circuit. When the junction temperature exceeds 160 ℃ (typical), the controller and current sources latch shut down. O ©On-Bright Electronics Diode & Inductor Short Protection When the Schottky diode or the inductor shorts, the current of the power MOSFET increasing significantly, which will cause the MOSFET permanent damage if the IC is continuously working. OB3353A will monitor the voltage on CS pin voltage cycle by cycle, if the voltage on CS pin is greater than 1.2V (typical) for continuous 17 cycles. The IC will latch shutdown the gate output to prevent the MOSFET from permanent damage. Confidential -8- Datasheet OB_DOC_DS_3353AA2 OB3353A High performance and Cost Effective LED Controller VIN: 10.8-13.2V HPWM: 100%, Max. Brightness; 1%Min. Brightness NA: Disable, 0-0.8V; Enable, 2-5V O nB rig ht c on fid en tia lt o 新 鼎 丰 Reference Application Figure5. OB3353A for HPWM to analog dimming Reference Application Schematic ©On-Bright Electronics Confidential -9- Datasheet OB_DOC_DS_3353AA2 OB3353A High performance and Cost Effective LED Controller Symbol Dimensions In Millimeters Min Max 1.350 1.750 0.050 0.250 1.250 1.650 0.310 0.510 0.100 0.250 4.700 5.150 3.800 4.000 5.800 6.200 1.270 (BSC) 0.400 1.270 0º 8º O nB rig A A1 A2 b c D E E1 e L θ ht c on fid en tia lt o 新 鼎 丰 PACKAGE MECHANICAL DATA ©On-Bright Electronics Confidential - 10 - 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 Datasheet OB_DOC_DS_3353AA2 OB3353A High performance and Cost Effective LED Controller on fid en tia lt o 新 鼎 丰 CPC8 O nB rig A A1 B B1 b C C1 C2 e L θ Dimensions In Millimeters Min Max 2.50 2.70 0.35 0.45 2.50 2.70 3.85 4.15 0.16 0.26 0.85 1.05 0.00 0.15 0.15 0.18 0.53(BSC) 0.40 0.60 0º 8º ht c Symbol ©On-Bright Electronics Confidential - 11 - Dimensions In Inches Min Max 0.098 0.106 0.014 0.018 0.098 0.106 0.152 0.163 0.006 0.010 0.033 0.041 0.000 0.006 0.006 0.007 0.021(BSC) 0.016 0.024 0º 8º Datasheet OB_DOC_DS_3353AA2 OB3353A High performance and Cost Effective LED Controller Important Notice O nB rig ht c on fid en tia lt o 新 鼎 丰 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 designed 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. ©On-Bright Electronics Confidential - 12 - Datasheet OB_DOC_DS_3353AA2