PAM2842TJR

High Power LED Driver Features n n n n n n n n n n n n PAM2842 Description The PAM2842 is a high power LED driver, capable of driving up to 10 high power LEDs in series. The PAM2842 supports buck, boost and sepic topology. The PAM2842 features over current protection , over voltage protection , under voltage lockout and over temperature protection, which prevent the device from damage. LED dimming can be done by using a PWM signal to the COMP pin. The PAM2842 is available in 40-Pin QFN6x6 and TSSOP-20 packages. Output Power up to 30W Chip Enable with Soft-start Analog and PWM Dimming Peak Efficiency up to 97% Low Quiescent Current Switching Frequency Adjustable Support Buck/Boost/Sepic Topology Over Current Protection Over Voltage Protection Thermal Protection UVLO Tiny Pb-Free Packages : 40-Pin QFN6x6 and TSSOP-20 Applications n Home Lighting n Automotive Lighting n Monitor Backlighting Typical Application Circuit Boost with Low Side Current Sense Vin 1μF L1 Boost with High Side Current Sense Vin L1 33 μ H 1μF 0.14Ω 33 μ H PGND PGND HVIN EN SW SW OV VDD-5V 1μF 1k Ω 10nF 10 μ F 0.14Ω 1μF 130kΩ 430kΩ PGND PGND HVIN 15kΩ SW SW OV VDD-5V 1μF 430kΩ PAM2842 COMP Sense+ Sense- EN 15kΩ 10nF PAM2842 COMP Sense+ Sense- 1k Ω VDD-DR 10 μ F 1μF 130kΩ VDD-DR RT AGND RT AGND Power Analog Microelectronics , Inc www.poweranalog.com 09/2008 Rev 1.1 1 High Power LED Driver Typical Application Circuit Buck/Boost (Sepic) with Low Side Current Sense Vin L1 PAM2842 Buck/Boost (Sepic) with High Side Current Sense Vin 1μF L1 10 μ F 56kΩ 0.14Ω 47 μ H 1μF 47 μ H L2 47 μ H 47 μ H L2 PGND PGND HVIN EN 10 μ F 1μF 130kΩ SW SW OV VDD-5V 1μF 220kΩ PGND PGND HVIN 12kΩ SW SW OV VDD-5V 1μF 220kΩ 12kΩ 10nF PAM2842 COMP Sense+ Sense- EN 1k Ω 10nF 10 μ F PAM2842 COMP Sense+ Sense- 1k Ω VDD-DR VDD-DR 1μF 0.14Ω 130kΩ RT AGND RT AGND Buck with High Side Current Sense Vin 0.14Ω 1μF 10 μ F PGND PGND HVIN EN SW L SW OV 47 μ H 1nF NC VDD-5V PAM2842 COMP Sense+ Sense- VDD-DR 10 μ F 1μF 130kΩ 1k Ω 100nF 12kΩ RT AGND Power Analog Microelectronics , Inc www.poweranalog.com 09/2008 Rev 1.1 2 High Power LED Driver B lock Diagram VDD_5V COMP OV SW SW PAM2842 HVIN LDO1 Comparator PWM + PWM Logic And Driver LDO2 VDD-DR Σ 100mV Reference + CS + GM - Ramp Generator Sense+ SenseEN FB Shutdown And Soft-start Adjustable Oscillator AGND RT PGND PGND Power Analog Microelectronics , Inc www.poweranalog.com 09/2008 Rev 1.1 3 High Power LED Driver P in Configuration & Marking Information Top View 6mm*6mm QFN NC NC NC NC NC NC NC NC NC NC PAM2842 TOP View TSSOP-20 40 PGND PGND PGND PGND PGND PGND NC HVIN EN 39 38 37 36 35 34 33 32 31 30 29 28 SW SW SW SW SW SW NC PGND PGND PGND PGND HVIN EN 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 NC SW SW SW OV VDD_5V COMP Sense+ Sense- 1 2 3 4 5 6 7 8 9 10 PAM2842 XXXYWWLL PAM2842 XXXYWWLL 27 26 25 24 23 22 21 VDD-DR RT AGND OV NC VDD_5V PGND PGND VDD-DR 11 12 13 AGND 14 Sense- 15 Sense+ 16 NC 17 COMP 18 NC 19 NC 20 NC X: Internal Code Y: Year WW: Week LL: Internal Code NC RT Pin Number QFN 6x6-40 1-6 8 9 10 12 13 14 15 17 21 23 25-30 7,11,16,18-20,22,24,31-40 TSSOP-20 1,2,3,4,10,11 5 6 7 8 9 12 13 14 15 16 17,18,19 20 Name PGND HVIN EN VDD-DR RT AGND SenseSense+ COMP VDD_5V OV SW NC Description Power Ground Input Chip Enable, Active High Internal LDO Output Frequency Adjustment Pin Analog Ground Sense resistor Sense resistor + Compensation Node Internal LDO Output Over Voltage Drain of Main Switch. No Connect Power Analog Microelectronics , Inc www.poweranalog.com 09/2008 Rev 1.1 4 High Power LED Driver A bsolute Maximum Ratings PAM2842 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 . Supply Voltage.............................................40V Output Current................................................1A I/O Pin Voltage Range.........GND-0.3V to V DD+0.3V Storage Temperature................ .....-40 OC to 125 OC Maximum Junction Temperature..................150 OC Soldering Temperature.......................300 OC, 5sec Recommended Operating Conditions Supply Voltage Range.........................5.5V to 40V O O Operation Temperature Range..........-40 C to 85 C Junction Temperature Range......... .-40 C to 150 C O O Thermal Information Parameter Thermal Resistance (Junction to Case) Thermal Resistance (Junction to Ambient) Symbol θJC θJA Package TSSOP QFN 6mm*6mm TSSOP QFN 6mm*6mm Maximum 20 7.6* 90 18.1* °C/W Unit *The Exposed PAD must be soldered to a thermal land on the PCB. Power Analog Microelectronics , Inc www.poweranalog.com 09/2008 Rev 1.1 5 High Power LED Driver E lectrical Characteristic PARAMETER Input Voltage Range ENA=high (no switching) ENA =high (1M switching frequency) Quiescent Current ENA =high (500k switching frequency) ENA =high (200k switching frequency) ENA =low Feedback Voltage, Low Side Feedback Voltage, High Side LED Current Line Regulation LED Current Load Regulation LDO Stage VDD_5V VDD_5V current_limit VDD_5V UVLO Threshold VDD_5V UVLO Hysteresis VDD_DR VDD_DR current_limit VDD_DR UVLO Threshold VDD_DR UVLO Hysteresis Switch Rdson Switch Current Limit Switch Leakage Current RT Voltage Switching Frequency* R RT =71kΩ R RT =30kΩ R RT =71kΩ R RT =180kΩ F SW =1MHz Min Duty Cycle F SW =500kHz F SW =200kHz Max Duty Cycle Vc Source Current Vc Sink Current Low Side Sense High Side Sense Feedback voltage=0 Feedback voltage=0 1.1 800k 400 160 No switching No switching No switching No switching No switching No switching No switching No switching Switch Stage VDD_5V=5V 0.1 3.5 50 1.2 1M 500 200 10 5 2.5 95 100 30 30 1.3 1.2M 600 240 Ω A μA V Hz kHz kHz % % % % % μA μA 4.5 14 3.7 4.5 14 3.7 5 74 4.0 200 5 50 4.0 200 5.5 90 4.3 5.5 90 4.3 V mA V mV V mA V mV V FB =VSENSE+ -AGND, VSE NSE-=AGND V FB =VSENSE+ - V SENS EIO=350mA 95 95 PAM2842 V EN=V DD=24V, 1Wx10 LEDs, T A=25°C, unless otherwise noted . Conditions Min 5.5 1 6 3 1.6 5 100 100 0.02 1.0 10 105 105 Typ Max 40 2 Units V mA mA mA mA μA mV mV %/V % * Switching Frequency FSW = 10 , reference value 24 ´ (RRT + 12k ) 12 Power Analog Microelectronics , Inc www.poweranalog.com 09/2008 Rev 1.1 6 High Power LED Driver Electrical Characteristic PARAMETER OV threshold Voltage OV Hysteresis Thermal-Shutdown Thermal-Shutdown Hysteresis Control Interface EN High EN Low 1.5 0.4 V V PAM2842 V EN=V DD=24V, 1Wx10 LEDs, T A=25 °C , unless otherwise noted . Conditions Fault Protection 1.1 1.2 70 150 30 1.3 V mV °C °C Min Typ Max Units Power Analog Microelectronics , Inc www.poweranalog.com 09/2008 Rev 1.1 7 High Power LED Driver Typical Performance Characteristic 1. Efficiency vs Input Voltage (Po=30W, 10X3W LEDs) 98% PAM2842 Boost mode, V EN=V DD=24V, 3W LED, Fsw=200kHz, T A=25 °C, unless otherwise noted . 2. Shutdown Current vs Input Voltage 6 5 Shutdown Current (uA) 97% 4 3 2 1 0 Efficiency 96% 95% 94% 93% 10 15 20 Input Voltage (V) 25 30 0 5 10 15 20 25 30 35 Input Voltage (V) 3. Quiescent Current vs Input Voltage 1.8 1.6 800 700 4. Output Current vs Input Voltage (10X3W LEDs) Quiescent Current (mA) 1.4 1.2 1 0.8 Switching 0.6 0 5 10 15 20 25 30 35 Input Voltage (V) No Switching Output Current (mA) 600 500 400 300 200 100 0 10 15 20 Input Voltage (V) 25 30 Low side Current sense High side Current sense 5. Output Current vs Temperature (V IN=12V, Load=10X3W LEDs) 800 750 Output Current (mA) 700 650 600 550 500 450 400 0 20 40 60 80 100 Ambient Temperature ( ℃) Power Analog Microelectronics , Inc www.poweranalog.com 09/2008 Rev 1.1 8 High Power LED Driver Typical Performance Characteristic Fsw=300kHz, T A=25°C, unless otherwise noted . 5. Output Current vs Input Voltage (Sepic mode, 1W LED), 400 350 Output Current (mA) PAM2842 6. Efficiency vs Input Voltage (Sepic mode, 1W LED), 90% 89% 88% 87% 300 Efficiency 5*1W 3*1W 1*1W 4*1W 2*1W 250 200 150 100 50 0 5 10 15 20 Input Voltage (V) 86% 85% 84% 83% 82% 81% 5 7 9 11 13 15 17 19 Input Voltage (V) 5*1W 3*1W 1*1W 4*1W 2*1W 7. Output Current vs Input Voltage (Buck mode, 3W LED), 0.8 0.7 8. Efficiency vs Input Voltage (Buck mode, 3W LED), 100% 95% 90% Output Current (A) 0.6 Efficiency 0.5 0.4 0.3 0.2 0.1 0 5 10 15 20 25 30 35 40 Input Voltage (V) 85% 80% 75% 1*3W 2*3W 3*3W 70% 5 10 15 20 25 30 35 40 Input Voltage (V) 400 350 9. LED Current vs Duty Cycle (PWM=100Hz, in Dimming State) 10. Start up and Shutdown LED Current (mA) 300 250 200 150 100 50 0 0 20 40 60 80 100 Duty Cycle (%) Vout EN Vcomp Power Analog Microelectronics , Inc www.poweranalog.com 09/2008 Rev 1.1 9 High Power LED Driver Application Information Topology Selection When maximum power supply voltage is below than minimum load voltage, select the boost topology. When minimum power supply voltage is high than maximum load voltage, select buck topology. When load voltage range is small and between the power supply voltage, select sepic topology. Table-1: Voltage condition Vs Topology For the large power application, if chose DCM, the peak current will be very large, it will have great electrical stress on the components, so we chose CCM. When work in CCM mode, a reasonable ripple current is chosen to Δ I L=0.4I L For the boost topology, PAM2842 Condition Vin max < Vo min Topology Boost Buck Sepic IL = D= IO 1- D Vinmin > Vomax Vo Ì Vin Inductor Selection VO - VIN VO DIL = VIN (VO - VIN ) LFVO The inductance, peak current rating, series resistance, and physical size should all be considered when selecting an inductor. These factors affect the converter'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 determine the inductor value. Large inductance can minimizes the current ripple, and therefore reduces the peak current, which decreases core losses in the inductor and I2R losses in the entire power path. However, large inductor values also require more energy storage and more turns of wire, which increases physical size and I2R 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 minimized but the inductor ripple current and peak current are higher than those in CCM. D: duty cycle, Io: output current, F: switching frequency. From above equation we can get the inductance: L= 2 2.5VIN (VO - VIN ) 2 FIO VO The inductor's current rating should be higher than IL + DIL 2 VO VIN For the buck topology, I L=I O D= DIL = (VIN - VO )VO LFVIN so L= 2.5VO (VIN - VO ) FIO VIN For the sepic topology, L1=L2 D IL1 = IO 1- D I L2=I O D= VO VIN + VO Power Analog Microelectronics , Inc www.poweranalog.com 09/2008 Rev 1.1 10 High Power LED Driver DIL = VIN VO LF(VIN + VO ) PAM2842 The ripple voltage is Chose so Δ I L=0.4I L1 L= 2 2.5VIN FIO (VIN + VO ) IOD FCS The voltage rating must be higher than input voltage. DVCs = Because the Cs capacitor will flow the large RMS current, so this topology is suitable for small power application. Diode Selection PAM2842 is a high switching frequency converter 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 3A, 40V with the PAM2842. Using a Schottky diode with a lower forward voltage drop is better to improve the power LED efficiency. In boost topology, the voltage rating should be higher than Vout and in buck topology, the voltage rating higher than Vin, the peak current is Capacitor Selection An input capacitor is required to reduce the input ripple and noise for proper operation of the PAM2842. For good input decoupling, Low ESR (equivalent series resistance) capacitors should be used at the input. At least 10 μ F input capacitor is recommended for most applications. And close the IC Vin-Pin we should add a bypass capacitor, usually use a 1 μ F capacitor. 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, 50V voltage rating capacitor is chosen. Consider from discharge aspect: Ix Δ t=Cx Δ V In boost and sepic topology, CO = In buck topology, CO = IDMAX = IL + DIL 2 in sepic topology, the voltage rating should be higher than Vin+Vout, the peak current is I DMAX=I L1peak+I L2peak The average current of the diode equals to Io. Work frequency selection PAM2842 working frequency is decided by resistor connect to the RT pin, it can be calculated by follow equation: 1012 FSW = (Hz) 24 ´ (RT + 12K) From the equations, we can see when working frequency is high, the inductance can be small. It's important in some size limit application. But we should know when the working frequency is higher, the switching loss is higher too. We must pay attention to thermal dissipation in this application. Methods for Setting LED Current There are two methods for setting and adjusting the LED current: 1) Rsense only 2) PWM signal with external components a) Use the COMP pin b) Use the Sense pin IOD FVRIPPLE IO (1 - D) FVRIPPLE V RIPPLE: Output voltage allowable ripple. Consider from equivalent series resistance: V ripple-esr=I co.ripplexC oesr In sepic topology, there is a series capacitor Cs between L1 and L2 (see application schematic), it flows the current: VO ICs(RMS) = IO VIN Power Analog Microelectronics , Inc www.poweranalog.com 09/2008 Rev 1.1 11 High Power LED Driver l Method 1: LED Current Setting with Resistor PAM2842 Rsense It maybe generate the audible noise in this dimming condition. l Method 3: LED Current Setting with PWM The most basic means of setting the LED current is connecting a resistor between Rsense+ and Rsense-. The LED current is decided by ISET Resistor Rsense. I LED =0.1/ R sense For flowing the large current, must pay attention to power dissipation on the resistor. Rsense has two position to select: high side current sense and low side current sense. In buck topology it just has high side current sense. In other topology we recommend use low side current sense for easier PCB layout. l Method 2: LED Current Setting with PWM Signal Using COMP Pin Signal using Sense Pin This method is turn PWM signal to DC voltage, the output current can be adjusted. Because the LED current is a adjustable DC value, it will cause LED color drift. Low side current sense and high side current sense circuit is different. Please see Figure 2 and 3. It use the internal reference voltage, so PWM dimming signal voltage is not considered, just meet the request of the MOSFET driving voltage. VDD_5V R1 D1 R2 R3 Sense+ R4 RTN This circuit uses resistor Rsense to set the on state current and the average LED current, then proportional to the percentage of off-time when the COMP pin is logic high. Here use a invert component 2N7002 (Q1) to isolate and invert the PWM signal (See Figure 1). Q1 PWM-DIM C1 C2 RSense Figure 2. PWM Dimming Use Sense Pin in Low Side Current Sense PAM2842 COMP Sense+ RSense Vo Q1 2N7002 PW M signal Ton Toff Q1 VDD_5V R3 R1 D1 SenseQ2 Figure 1. PWM Dimming Use COMP Pin Average LED current is approximately equal to: TI IAVG = OFF LED TON + TOFF Also, the recommended PWM frequency is between 100Hz and 200Hz. Frequency 200Hz, the average LED current will have a large error when duty cycle is small (