PAM2846

PAM2846 Integrated 6 String LED Boost Type Driver F eatures n Six Constant-Current Output Channels n Parallel Channels Allow Higher Current per LED String n Maximum 40V Continuous Voltage Output Limit for Each Channel n Self-adaptive Vout to Fit Different LED Number n Adjustable Constant LED Current n Drives 10 or more LEDs Each String as Long as the String Voltage Less Than 40V n Internal 2.5A Power MOSFET n Low 400mV Feedback Voltage at Full Current Improves Efficiency n Allows Digital PWM and Analog Dimming n Wide (100:1) PWM Dimming Range without Color Shift n Independent Dimming and Shutdown Control of the LED Driver n ±1% Typical Current Matching between Strings n Open LED Protection: Adjustable Clamp Voltage n Short LED Protection n 3 Frequencies Selection: 1.6MHz/1MHz/500kHz n Wide Input Voltage Range: 4.8V to 28V n Over Temperature Protection n Available in 24-pin 4mmx4mm QFN Package n Pb-free Package Description The PAM2846 is a high-efficiency boost type LED driver. It is designed for large LCD panel that employs an array of LEDs as back light source. The PAM2846 employs a current-mode step-up converter that drives six parallel strings of LEDs connected in multiple series. This built-in stringcurrent-control circuit achieves ±1% typical current matching between strings, which ensures even brightness for all LEDs. The device is able to adapt to different numbers of LEDs in each string or different forward voltage for different types of LEDs and keep the string current constant. Separate feedback loops limit the output voltage if one or more LEDs open or short. The limit voltage of over voltage protection is adjustable by changing the feedback resistor ratio. The PAM2846 has features cycle-by-cycle current limit to provide consistent operation and soft-start capability. A thermal-shutdown circuit provides another level of protection. The PAM2846 has a wide +4.8V to +28V inputvoltage range and provides adjustable full-scale LED current. The switching frequency of this device can be selected among 500kHz, 1MHz and 1.6MHz according to the application requirements. Applications n White or RGB Backlighting for LCD TV, LCD Monitor, Notebook, Handy Terminals, and Avionics Displays Panels n LED Lighting Devices Typical Application VIN: 4.8V to 28V 22 μ H 3A/40V L SW SW SW OVP R2 VIN ENA PWMD Fsel PWMD Fsel R1 300k Total 10 LEDs per string PAM2846 VC Vcc-5V Vcc-driver 0-10k 1μ 1μ 10K 100nF GND LED1 LED2 LED3 LED4 LED5 LED6 9.2k Iset PGND PGND PGND Power Analog Microelectronics , Inc www.poweranalog.com 07/2008 Rev 1.2 1 PAM2846 Integrated 6 String LED Boost Type Driver B lock Diagram VIN Vcc-5V Vcc-driver LDO1 LDO2 UVLO 1.2V SOFT START 1.6MHz 1MHz 500KHz OVP Fsel ENA ENABLE OVP SLOPE COMPENSATION PWM COMPATATOR OTP Bandgap POR VC LED Feedback 1.2V MAIN CONTROL Level Shift Driver + SW EA CURRENT LIMIT LED1-6 CS AMP PGND LED1 LED2 LED3 LED4 LED5 LED6 PWMD PWM DIMMING led short protect led short protect led short protect led short protect led short protect led short protect I_set AMP Iset GND Power Analog Microelectronics , Inc www.poweranalog.com 07/2008 Rev 1.2 2 PAM2846 Integrated 6 String LED Boost Type Driver P in Configuration QFN 4mmX4mm 24 1 2 3 4 5 6 7 8 9 10 11 12 23 22 21 20 19 18 17 P2846 XXXYW 16 15 14 13 XXX: Internal Code Y: Year W: Weekly Pin Descriptions Pin Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Name VIN Vcc-driver GND ENA PWMD LED1 LED2 LED3 GND GND LED4 LED5 LED6 Iset Vcc-5V VC Fsel OVP PGND PGND PGND SW SW SW Description Supply input 5V linear regulator output for power MOS driver Ground Enable input PWM dimming control LED1 cathode terminal LED2 cathode terminal LED3 cathode terminal Ground Ground LED4 cathode terminal LED5 cathode terminal LED6 cathode terminal LED current adjustment pin 5V linear regulator output Boost stage compensation pin Oscillator frequency selection pin Over voltage protection Power ground Power ground Power ground Power MOS drain Power MOS drain Power MOS drain Power Analog Microelectronics , Inc www.poweranalog.com 07/2008 Rev 1.2 3 PAM2846 Integrated 6 String LED Boost Type Driver A bsolute Maximum Ratings These are stress ratings only and functional operation is not implied . Exposure to absolute maximum ratings for prolonged time periods may affect device reliability . All voltages are with respect to ground . O O VIN,ENA.....................................-0.3V To +30V Junction Temperature Range.......-40 C to 125 C O O SW ,LED.....................................-0.3V To +40V Storage Temperature..................-40 C to 150 C O Vcc-5V,Vcc-driver,VC....................-0.3V To +6V Maximum Junction Temperature...............150 C O PWMD,Fsel,OVP,Iset.....................-0.3V To +6V Soldering Temperature....................300 C,5sec Recommended Operating Conditions Supply Voltage Range.......................4.8V to 28V Operating Temperature.................-20 OC to 85 OC Thermal Information Parameter Thermal Resistance (Junction to Case) Thermal Resistance (Junction to Environment) Package 4x4mm QFN 4x4mm QFN Symbol θjC θjA Maximum 2 37 Unit °C/W °C/W Power Analog Microelectronics , Inc www.poweranalog.com 07/2008 Rev 1.2 4 PAM2846 Integrated 6 String LED Boost Type Driver E lectrical Characteristic PARAMETER Input Voltage Range ENA=high (no switching) Fsel=high (1.6M switching frequency) Quiescent Current Fsel =high (1M switching frequency) Fsel =high (500k switching frequency) ENA=low LDO Stage Vcc_5V Vcc_5V current_limit Vcc_5V UVLO Threshold Vcc_5V UVLO Hysteresis Vcc_driver Vcc_driver current_limit Vcc_driver UVLO Threshold Vcc_driver UVLO Hysteresis Boost Stage Switch Rdson Switch Current Limit Switch Leakage Current Fsel =Vcc_5V Switching Frequency Fsel =Open Fsel =Gnd Fsel =Vcc_5V Minimums Duty Cycle Fsel =Open Fsel =Gnd Maximums Duty Cycle VC Source Current VC Sink Current Vcc_5V=5V 0.2 2.5 1 1.6 1.0 500 20 10 5 90 Ω A μA MHz MHz kHz % % % % μA μA T A=25°C, V IN=ENA=12V, L=22 μ H, Rset=10k Ω , unless otherwise noted Conditions Min 4.8 1 10 6 3 5 20 μA Typ Max 28 2 mA Units V No switching No switching No switching No switching No switching No switching No switching No switching 4.7 14 3.9 4.7 14 3.9 5 74 4.2 70 5 74 4.2 70 5.5 90 4.5 5.5 90 4.5 V mA V mV V mA V mV 60 60 Power Analog Microelectronics , Inc www.poweranalog.com 07/2008 Rev 1.2 5 PAM2846 Integrated 6 String LED Boost Type Driver E lectrical Characteristic PARAMETER LED Controller Stage I=190*1.2V/Riset, Riset=7.68k Full-Scale LED_Output Current I=190*1.2V/Riset, Riset=11.3k I=190*1.2V/Riset, Riset=22.6k LED current matching Iset Voltage Minimums LED voltage Analog Dimming Range PWM Dimming Frequency Fault Protection LED_ Overvoltage Threshold LED_ Overvoltage Hysteresis Overvoltage Threshold Overvoltage Hysteresis Thermal-Shutdown Thermal-Shutdown Hysteresis Controll Interface EN High EN Low PWMD High PWMD Low Fsel High Fsel Midlevel Fsel Low EN Min pulse width EN Max pulse width EN off delay Vcc_5V- 0.5 T A=25°C, V IN=ENA=12V, L=22 μ H, Rset=10k Ω , unless otherwise noted . Conditions Min Typ 30 20 10 -3 1 1.2 400 I=190*1.2V /Riset I/32 100 4.6 4.9 1 1.2 80 150 30 I 1k 5.1 +3 Max Units mA mA mA % V mV mA Hz V V V mV °C °C 1.5 0.4 1.5 0.4 V V V V V 2 0.5 V V μs 10 200 μs μs 1 single wire dimming low level single wire dimming low level single wire dimming low level 0.5 Power Analog Microelectronics , Inc www.poweranalog.com 07/2008 Rev 1.2 6 PAM2846 Integrated 6 String LED Boost Type Driver Typical Performance Characteristic T A=25°C, V IN=ENA=12V, Rset=10k Ω , L=22 μ H, Fsw=500kHz, 10x6 LEDs, unless otherwise noted 100% 90% 80% 70% Efficiency Input Voltage VS Efficiency LED Current VS PWMD Duty cycle@100Hz 25 20 LED current (mA) 60% 50% 40% 30% 20% 10% 0% 5 9 13 17 21 25 Input Voltage (V) Fsw =500KHz Fsw =1MHz Fsw =1.6MHz 15 10 5 0 20% 40% 60% Duty cycle 80% 100% Shutdown current VS Input Voltage 6 10 Quiescent current VS Input Voltage Shutdown current (uA) 5 Supply Current (mA) 8 PWMD=0 Fsw=500KHz Fsw=1MHz Fsw=1.6MHz 4 3 2 1 0 0 10 20 30 Input voltage (V) 6 4 2 0 6 10 14 18 22 26 Input Voltage Power Analog Microelectronics , Inc www.poweranalog.com 07/2008 Rev 1.2 7 PAM2846 Integrated 6 String LED Boost Type Driver Typical Performance Characteristic T A=25°C, V IN=ENA=12V, Rset=10k Ω , L=22 μ H, Fsw=500kHz, 10x6 LED, unless otherwise noted Total LED Current Line regulation 137.5 137 Efficiency VS Input Voltage 100% 95% 136.5 LED Current (mA) Efficiency 136 135.5 135 134.5 90% 85% 80% 10x6 LED 8x6 LED 6x6 LED 134 133.5 4 8 12 16 20 24 28 75% 4 8 12 16 20 24 28 Input Voltage (V) Input Voltage (V) Analog Dimming Signal Step 25 20 15 10 5 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 ENA Dimming Step Max Output Current Vs Output Voltage (Per Channel) 100 Max Output Current (mA) LED Current (mA) 80 60 40 20 Vin=12V Vin=6V 0 16 20 24 28 32 36 40 Output Voltage (V) Power Analog Microelectronics , Inc www.poweranalog.com 07/2008 Rev 1.2 8 PAM2846 Integrated 6 String LED Boost Type Driver Typical Performance Characteristic T A=25°C, V IN=ENA=12V, Rset=10k Ω , L=22 μ H, Fsw=500kHz, 10x6 LEDs, unless otherwise noted. PWM Dimming (Duty Cycle=20%) PWMD DC coupling V LED1 DC coupling LED Current Waveforms (PWMD=50%) PWMD DC coupling V LED1 DC coupling I LED DC coupling I LED DC coupling LED Current Waveforms ( PWMD =80%) Startup Waveforms PWMD DC coupling V LED1 DC coupling Vout DC coupling IL DC coupling I LED DC coupling ENA DC coupling Start up and Shutdown Waveforms Stable Operation Vout DC coupling IL DC coupling ENA DC coupling Vsw DC coupling IL DC coupling Power Analog Microelectronics , Inc www.poweranalog.com 07/2008 Rev 1.2 9 PAM2846 Integrated 6 String LED Boost Type Driver Application Information I nductor Selection The inductance, peak current rating, series resistance, and physical size should all be considered when selecting an inductor. These factors affect the conver ter's operating mode, efficiency, maximum output load capability, transient response time, output voltage ripple, and cost. The maximum output current, input voltage, output voltage, and switching frequency d e t e r m i n e t h e i n d u c t o r v a l u e . Ve r y h i g h inductance minimizes the current rip ple, and therefore reduces the peak current, which 2 decreases core losses in the inductor and I R losses in the entire power path. However, large inductor values also require more energy storage and more turns of wire, which increases physical 2 size and I R copper losses in the inductor. Low inductor values decrease the physical size, but increase the current ripple and peak current. Finding the best inductor involves the compromises among circuit efficiency, inductor size, and cost. When choosing an inductor, the first step is to determine the operating mode: continuous conduction mode (CCM) or discontinuous conduction mode (DCM). When CCM mode is chosen, the ripple current and the peak current of the inductor can be minimized. If a small-size inductor is required, DCM mode can be chosen. In DCM mode, the inductor value and size can be mini mized but the inductor ripple current and peak current are higher than those in CCM. Capacitor Selection An input capacitor is required to reduce the input ripple and noise for proper operation of the PAM2846. For good input decoupling, low ESR (equivalent series resistance) capacitors should be used at the input. At least 2.2 μ F input capacitor is recommended for most applications. A minimum output capacitor value of 10 μ F is recommended under normal operating conditions, while a 22 μ F or higher capacitor may be required for higher power LED current. A reasonable value of the output capacitor depends on the LED current. The total output voltage ripple has two components: the capacitive ripple caused by the charging and discharging on the output capacitor, and the ohmic ripple due to the capacitor's equivalent series resistance. The ESR of the output capacitor is the important parameter to determine the output voltage ripple of the converter, so low ESR capacitors should be used at the output to reduce the output voltage ripple. The voltage rating and temperature characteristics of the output capacitor must also be considered. So a value of 10 μ F, voltage rating (50V) capacitor is chosen. Diode Selection PAM2846 is high switching frequency convertor, w h i c h d e m a n d s h i g h s p e e d r e c t i f i e r. I t ' s indispensable to use a Schottky diode rated at 2A, 60V with the PAM2846. Using a Schottky diode with a lower forward voltage drop can improve efficiency of the convertor. The voltage rating of the diode should be greater than the output voltage. Methods for Setting LED Current There are three methods for setting and adjusting the LED current outlined here. The methods are: 1) RSET only 2) PWM Input at PWMD 3) Single wire logic signal at ENA >10ms 0 1 2 3 4 5 27 28 29 30 31 32 ENA t SOFT-START 32/32 31/32 500ns