PAM2845

40V High Power Boost Convertor with 6 Channel Constant Current Source Features 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 Adjustable Constant Output Voltage 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 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 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 PAM2845 Description The PAM2845 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 PAM2845 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. Separate feedback loops limit the output voltage if one or more LEDs open or short. The PAM2845 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 PAM2845 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 10 μ F 22 μ H 3A/40V L SW SW SW FB R2 10 μ F VIN ENA PWMD Fsel PWMD Fsel R1 270kΩ Total 10 LEDs per string PAM2845 VC Vcc-5V Vcc-driver 100nF 1μF Iset 1μF 10kΩ GND LED1 LED2 LED3 LED4 LED5 LED6 9.1kΩ PGND PGND PGND Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.0 1 40V High Power Boost Convertor with 6 Channel Constant Current Source B lock Diagram VIN PAM2845 Vcc-5V Vcc-driver LDO1 LDO2 UVLO SLOPE COMPENSATION PWM COMPATATOR FB SOFT START 1.6MHz 800KHz 500KHz Fsel ENA ENABLE OTP Bandgap 1.2V MAIN CONTROL Level Shift Driver + SW EA CURRENT LIMIT POR VC CS AMP PWMD PWM DIMMING PGND LED1 LED2 LED3 LED4 LED5 LED6 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 08/2008 Rev 1.0 2 40V High Power Boost Convertor with 6 Channel Constant Current Source P in Configuration QFN 4X4 24 1 2 3 4 5 6 7 8 9 10 11 12 23 22 21 20 19 18 17 PAM2845 P2845 XXXYW 16 15 14 13 X: Internal Code Y: Year W: Week 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 FB 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 Feedback Power ground Power ground Power ground Power MOS drain Power MOS drain Power MOS drain Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.0 3 40V High Power Boost Convertor with 6 Channel Constant Current Source A bsolute Maximum Ratings PAM2845 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 . VIN,ENA.....................................-0.3V To +30V Operating Temperature...............-40 OC to 125 OC SW ,LED.....................................-0.3V To +40V Storage Temperature..................-40 OC to 150 OC Vcc-5V,Vcc-driver,VC....................-0.3V To +6V Maximum Junction Temperature...............150 OC PWMD,Fsel,FB,Iset.......................-0.3V To +6V Soldering Temperature....................300 OC,5sec Recommended Operating Conditions Supply Voltage Range.......................4.8V to 28V Operation Temperature Range.........-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 20 37 Unit °C/W °C/W Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.0 4 40V High Power Boost Convertor with 6 Channel Constant Current Source E lectrical Characteristic T A=25°C, V IN=ENA=12V, L=22 μ H, Rset=10k Ω, unless otherwise noted 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 Feedback Voltage 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 1.2 0.2 2.5 1 1.6 1.0 500 20 10 5 90 V Ω A μA MHz MHz kHz % % % % μA μA 4.5 14 3.9 4.5 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 Conditions Min 4.8 1 10 6 3 5 20 μA Typ Max 28 2 mA Units V PAM2845 60 60 Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.0 5 40V High Power Boost Convertor with 6 Channel Constant Current Source Electrical 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 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 100 0.5 10 Vcc_5V-0.5 PAM2845 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 1 150 30 1.5 0.4 1.5 0.4 1 2 0.5 I 1k 5.1 +3 Max Units mA mA mA % V mV mA Hz V V °C °C V V V V V V V μs μs μs Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.0 6 40V High Power Boost Convertor with 6 Channel Constant Current Source Typical Performance Characteristic T A=25°C, V IN=ENA=12V, L=22 μ H, Rset=10k Ω , unless otherwise noted. 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 5 PAM2845 Input Voltage VS Efficiency 25 20 LED current(mA) LED Current VS PWMD Duty cycle Efficiency(%) 15 10 5 0 9 13 Input voltage(V) 17 21 20% 40% 60% Duty cycle 80% 100% Shutdown current VS Input Voltage 6 Shutdown current(uA) Supply Current (mA) Quiescent Current VS Input Voltage 9 8 7 6 5 Fsw=1MHz Fsw=1.6MHz 5 4 3 2 1 0 0 10 20 30 Input voltage(V) 4 3 2 1 0 6 10 PWMD=0 Fsw=500KHz 14 18 22 Input Voltage (V) 26 Vout Line Regulation 41 40.5 Output Voltage (V) Total LED Current Line regulation 133 132.5 40 39.5 39 38.5 38 4.5 8 12 16 20 24 28 Input Voltage (V) LED Current (mA) 132 131.5 131 130.5 130 129.5 129 4.5 8 12 16 20 24 28 Input Voltage (V) Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.0 7 40V High Power Boost Convertor with 6 Channel Constant Current Source Typical Performance Characteristic T A=25°C, V IN=ENA=12V, L=22 μ H, Rset=10k Ω , unless otherwise noted. Efficiency VS Input Voltage 100% 6x6 LED 8x6 LED 10x6 LED Efficiency PAM2845 Start up and Shutdown waveforms 95% 90% 12x6 LED Vout DC coupling IL DC coupling ENA DC coupling 85% 80% 75% 4.5 8 12 16 20 Input Voltage(V) 24 28 Switching Waveforms Inductor Current Waveforms( PWMD =20%) Vsw DC coupling IL DC coupling PWMD DC coupling V LED1 DC coupling IL DC coupling LED Current Waveforms( PWMD =20%) PWMD DC coupling V LED1 DC coupling Inductor Current Waveforms( PWMD =50%) PWMD DC coupling V LED1 DC coupling I LED DC coupling IL DC coupling Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.0 8 40V High Power Boost Convertor with 6 Channel Constant Current Source Typical Performance Characteristic T A=25°C, V IN=ENA=12V, L=22 μ H, Rset=10k Ω , unless otherwise noted. LED Current Waveforms(PWMD=50%) PWMD DC coupling V LED1 DC coupling PWMD DC coupling V LED1 DC coupling PAM2845 Inductor Current Waveforms( PWMD =80%) I LED DC coupling IL 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 Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.0 9 40V High Power Boost Convertor with 6 Channel Constant Current Source 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 PAM2845. For good input decoupling, Low ESR (equivalent series resistance) capacitors should be used at the input. At least 2.2uF input capacitor is recommended for most applications. A minimum output capacitor value of 10uF is recommended under normal operating conditions, while a 22uF 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 10uF, voltage rating(50V) capacitor is chosen. Diode Selection PAM2845 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 PAM2845. Using a Schottky diode with a lower forward voltage drop is better to improve the power LED efficiency, and its voltage rating 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) PWM Input at ENA PAM2845 >10ms 0 1 2 3 4 5 27 28 29 30 31 32 ENA t SOFT-START 32/32 31/32 500ns