PAM2841 1.5A SW Current, 40V Precision WLED Driver Features n n n n n n n n n n n Description Capable of Driving 10 or more WLEDs Chip Enable with Soft-start Analog and PWM Dimming Peak Efficiency up to 90% Low Quiescent Current Fixed Frequency of 1MHz Over Current Protection Over Voltage Protection Thermal Protection UVLO Tiny Pb-Free Packages (RoHS Compliant): MSOP-8 and DFN 2X2 The PAM2841 is a white LED driver, capable of driving 10 or more WLEDs in series (depending on forward voltage of the LEDs) with a range of input voltages from 2.7V to 5.5V. The PAM2841 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 four methods as described in the Application Information hereinafter. Applications n WLED Driver System Typical Application D1(SS14) L1 V IN 22 μ H C1 10 μ F PGND SW R1 910kΩ C3 1μF VIN C2 ENA 1μF OVP PAM2841 Comp R2 27kΩ FB 10 LEDs GND C4 10nF R3 10Ω D1(SS14) V IN L1 C1 22 μ H 10 μ F PGND SW R1 910kΩ C3 1μF VIN C2 PAM2841 ENA 1μF 3x9 LEDs OVP Comp R2 27kΩ FB GND R3 1.1Ω C4 10nF Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 1 PAM2841 1.5A SW Current, 40V Precision WLED Driver Block Diagram Comp 200mV Reference FB OVP SW VIN Comparator + GM - PWM + PWM Logic And Driver + Σ CS Ramp Generator ENA Shutdown And Soft-start 1.0MHz Oscillator GND PGND Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 2 PAM2841 1.5A SW Current, 40V Precision WLED Driver Pin Configuration & Marking Information TOP View MSOP-8 8 1 P2841 XXXYW 2 3 7 XXX: Internal Code Y: Year W: Weekly 6 4 5 DFN2X2 1 3 EMX YW 2 8 7 6 4 EM: Product Code X: Internal Code Y: Year W: Weekly 5 Pin number Name Description 1 PGND Power Ground 2 VIN Input Voltage 3 ENA Chip Enable, Active High 4 Comp Compensation Node 5 GND Chip Ground 6 FB 7 OVP Over Voltage 8 SW Drain of Main Switch. Feedback Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 3 PAM2841 1.5A SW Current, 40V Precision WLED Driver Absolute 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 Supply Voltage.............................................6.0V Output Current............................................50mA I/O Pin Voltage Range.........GND-0.3V to V DD+0.3V Maximum SW Pin Voltage...............................40V O Storage Temperature.....................-40 C to 150 C O Maximum Junction Temperature..................150 C O Soldering Temperature.......................300 C,5sec Recommended Operating Conditions Junction Temperature Range.............0 OC to 125 OC Supply Voltage Range........................2.8V to 5.5V O O Operation Temperature Range..........-40 C to 85 C Thermal Information Parameter Symbol Thermal Resistance θJA (Junction to Ambient) Thermal Resistance θJC (Junction to Case) Package Maximum Unit MSOP 180 °C/W DFN 102 °C/W MSOP 40 °C/W DFN 20 °C/W Electrical Characteristic V EN=V DD=5.0V, 10 LEDs, T A=25 C , unless otherwise noted . O Parameters Supply Voltage Range Symbol Test Conditions VDD IQ No Switching Shutdown Current ISD VENA=low IＯ 200 R3=5.1Ω 40 R3=6.8Ω 30 R3=10Ω 20 R3=20Ω 10 Output Voltage Range VO Feedback Voltage VFB SW On Resistance RDS(ON) SW Current Limit ILIM SW Frequency fSW Maximum Duty Cycle DC Over Voltage Protection Threshold OVP Open Load VEL Chip Shutdown VEH Chip On 1.2 UVLO VIN falling 2.0 Enable Threshold Voltage Under Voltage Lockout TYP. 2.7 Quiescent Current Output Current MIN. VINx1.1 MAX. UNITS 5.5 V 300 μA 1 μA mA 40 V 200 206 mV ISW=100mA 0.35 0.5 Ω Switch On 1.5 VENA=high 194 0.7 1.0 A 1.3 MHz 95 % 1.2 V 0.4 2.2 2.4 V V UVLO Hysterisis VTH 0.2 V Over Temperature Shutdown OTS 150 °C Over Temperature Hysterisis OTH 30 °C Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 4 PAM2841 1.5A SW Current, 40V Precision WLED Driver Typical Operating Characteristics T A=25 ° C,V DD=5V, unless otherwise noted . 2. Efficiency VS Load Current 1. Efficiency VS Input Voltage 6 LED, L=22 µ H 90% 95 % 85% 90 % 80% 85 % 75% Efficiency Efficiency I LED=20mA, L=22 µ H 70% 65% 60% 8LED 12LED 2 3 4 5 V DD =5V VDD=3.6V 65% 10LED 50% 75% 70% 6LED 55% 80 % 60% 6 0 10 20 Input Voltage(V) 30 40 50 60 Output Current(mA) 3. Efficiency VS Input Voltage 4. LED Current V S Output Voltage L= 47µ H I LED=20mA, 10 LED 0.5 0.9 VDD=5V VDD=3V 0.85 LED Current (A) 0.4 Efficiency 0.8 0.75 0.7 L=4.7uH L=10uH L=22uH L=33uH L=47uH 0.65 0.3 0.2 0.1 0 0.6 2 3 4 5 6 8 Input Voltage(V) 12 16 20 24 28 32 Output Voltage (V) Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 5 36 PAM2841 1.5A SW Current, 40V Precision WLED Driver Typical Operating Characteristics T A=25 ° C,V DD=5V, unless otherwise noted . 5. Feedback Voltage VS Input voltage 6. Feeback Voltage VS Temperature 10 LED, ILED=20mA 0.3 0.25 0.25 0.2 0.2 Vfb(V) 0.3 0.15 0.15 0.1 0.1 0.05 0.05 0 0 2 3 4 5 6 0 20 40 Input Voltage (V) 60 80 100 120 140 Temperature 8. Frequency VS Input Voltage 7. LED current VS Input voltage 10 LED L=22 μ H, 10 LED 25 1.2 20 1 Frequency(Mhz) ILED(mA) Vfb (V) 10 LED, ILED=20mA 15 10 0.8 0.6 0.4 R=10 5 0.2 R=15 R=20 0 0 2 3 4 5 2 6 3 4 5 6 Input Voltage(V) Vin(V) Power Analog Microelectronics , Inc www.poweranalog.com 6 08/2008 Rev 1.3 PAM2841 1.5A SW Current, 40V Precision WLED Driver Typical Operating Characteristics T A=25 ° C,V DD=5V, unless otherwise noted . 10. Frequency VS Temperature ( 10 LED, I LED=20mA) 200 1.13 180 1.12 160 Frequency(Mhz) Quiescent Current (uA) 9. Quiescent Current VS Input Voltage 140 120 100 80 60 1.11 1.1 1.09 1.08 1.07 40 1.06 20 0 1.05 2 3 4 5 0 6 20 Input voltage (V) 40 60 80 100 120 140 Temperature 11. LED Current VS Duty Cycle of PWM (PWM@EN Pin) 12. LED Current VS Duty Cycle of PWM (PWM@COMP Pin) 25 20 18 20 Theoretic LED Current(mA) LED Current (mA) 16 14 12 f=100Hz 10 8 6 f=100HZ 4 f=200Hz 2 0 0% 40% 60% 80% 10 5 f=200Hz theoretic 20% 15 0 0% 100% 20% 40% 60% 80% 100% Duty Cycle of PWM Duty Cycle of PWM Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 7 PAM2841 1.5A SW Current, 40V Precision WLED Driver Typical Operating Characteristics T A=25 ° C,V DD=5V, unless otherwise noted . 13. Start-up Waveform 14. Steady State Waveform Vin=5V,10LED,Iled=20mA Vin=5V,10LED,Iled=20mA ENA DC coupling SW DC coupling IL DC coutpling IL DC coupling VOUT DC coupling Vout AC coupling 15.Open load 16. Open load Vout AC coupling Vout DC coutpling OVP AC coupling SW DC coupling SW DC coutpling Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 8 PAM2841 1.5A SW Current, 40V Precision WLED Driver Application Information Inductor Selection to the device. The selection of the inductor affects steady state operation as well as transient behavior and loop stability. These factors make it the most important component in power regulator design. There are three important inductor specifications, inductor value, DC resistance and saturation current. Considering inductor value alone is not enough. Output Capacitor The output capacitor is mainly selected to meet the requirement for the output ripple and loop stability. This ripple voltage is related to the capacitor's capacitance and its equivalent series resistance (ESR). A output capacitor of 1μF minimum is recommended and maybe need a larger capacitor. 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 (ESR): The inductor value determines the inductor ripple current. Choose an inductor that can handle the necessary peak current without saturation, the inductor DC current given by: Iin_dc=Vout*Iout/(Vin* η ) η =efficiency. V RIPPLE=V RIPPLE(C)+V RIPPLE(ESR) Inductor values can have ±20% tolerance with no current bias. When the inductor current approaches saturation level, its inductance can decrease 20% to 35% from the 0A value depending on how the inductor vendor defines saturation current. Using an inductor with a smaller inductance value causes discontinuous PWM when the inductor current ramps down to zero before the end of each switching cycle. This reduces the boost converter's maximum output current, causes large input voltage ripple and reduces efficiency. Large inductance value provides much more output current and higher conversion efficiency. For these reasons, an inductor within 4.7μH to 22μH value range is recommended. V RIPPLE(C)≈ 2 I OUT) 1/2*(L/(C OUT *((V OUT(MAX) -V IN(MIN) ))))*(I 2 PEAK - V RIPPLE(ESR)=I PEAK*R ESR(COUT) Where I PEAK is the peak inductor current. Multilayer ceramic capacitors are an excellent choice as they have extremely low ESR and are available in small footprints. Capacitance and ESR variation with temperature should be considered for best performance in applications with wide operating temperature ranges. Dimming Control Schottky Diode Selection There are 4 different types of dimming control methods: The high switching frequency of the PAM2841 demands a high-speed rectification for optimum efficiency. Ensure that the diode average and peak current rating exceeds the average output current and peak inductor current. In addition, the diode's reverse breakdown voltage must exceed the open protection voltage. 1). Using an External PWM Signal to EN Pin With the PWM signal applied to the EN pin, the PAM2841 is alternately turned on or off by the PWM signal. The LEDs operate at either zero or full current. The average LED current changes proportionally with the duty cycle of the PWM signal. A 0% duty cycle turns off the PAM2841 and leads to zero LED current. A 100% duty cycle generates full current.Also the recommend dimming frequency is between 100Hz and 200Hz. Input and Output Capacitor Selection Input Capacitor At least a 1 μ F input capacitor is recommended to reduce the input ripple and switching noise for normal operating conditions. Larger value and lower ESR (Equivalent Series Resistance) may be needed if the application require very low input ripple. It follows that ceramic capacitors are a good choice for applications. Note that the input capacitor should be located as close as possible I AVE=I STATE* (T ON –T STARTUP)/(T ON+T OFF) where T ON: on time of a period T STARTUP: 0.85ms T OFF: off time of a period I STATE: on state current (full current) Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 9 PAM2841 1.5A SW Current, 40V Precision WLED Driver L1 1 VIN 2 1 3). Using a DC Voltage For some applications, a simple and direct way to control brightness is use an external variable DC voltage to vary the voltage drop on feedback resistor. This will make the PAM2841 adjust the output current to follow the change of feedback voltage. The circuit is shown in Figure 3. As the DC voltage increases, the voltage drop on R4 increases and the voltage drop on R3 decreases. Thus, the LED current decreases. The selection of R4 and R5 will make the current from the variable DC source much smaller than the LED current and much larger than the FB pin current. For VCC range from 0V to 2V, the selection of resistors in Figure 3 gives dimming control of LED current from 0mA to 20mA. D1 2 22uH C1 10uF C3 1uF R1 910k U12 1 0 2 3 1uF C2 4 8 PGND SW VIN OV OVP ENA FB COMP 7 0 6 R2 27k 5 GND PAM2841 PWM C4 10n Figure. 1 2). Using an External PWM Signal to NMOS Gate. When PWM signal is at high level, N MOSFET turned on, then pull comp pin down, then the LED current should be zero. When PWM signal is at low level, N MOSFET turned off. The circuit uses resistor R1 to set the on state current. The average LED current changes proportionally with the duty cycle of the PWM signal. A 100% duty cycle turns off the PAM2841 and leads to zero LED current. A 0% duty cycle generates full current. L1 1 VIN 2 1 D1 2 22uH C1 10uF C3 1uF R1 910k U33 1 0 PGND 2 3 1uF SW VIN OV OVP ENA C2 4 FB COMP GND 8 7 0 R2 27k 6 5 PAM2841 ENA C4 10n R4 R5 90k 5k R3 10 I AVE=I STATE* (T ON –T STARTUP)/(T ON+T OFF) Figure. 3 where T ON: on time of a period T STARTUP: 0.08ms T OFF: off time of a period I STATE: on state current (full current) Also the recommend frequency is between 100 and 500Hz. Frequency<100Hz can naturally causes LEDs to blink visibly. L1 1 VIN 2 1 4). Using a Filtered PWM Signal The filtered PWM signal can be considered as an adjustable DC voltage. Such regulated signal is often with some grade of ripple because of some simple configuration of circuit. With appropriated arrangement of PWM frequency and level, and filter parameters, it can be used to replace the variable DC voltage source in dimming control. The circuit is shown in Figure 4. D1 2 22uH C1 10uF C3 1uF DC R1 910k U12 1 0 2 3 1uF C2 4 PGND SW VIN OV OVP ENA FB COMP GND 8 7 6 0 L1 R2 27k 1 VIN 2 1 D1 2 22uH 5 C1 10uF C3 1uF PAM2841 ENA Q1 PWM R1 910k U33 1 0 2 C4 10n 3 1uF R3 10 C2 4 PGND SW OVP OV VIN ENA FB COMP GND 8 7 0 R2 27k 6 5 PAM2841 ENA C4 10n R4 R5 90k Figure. 2 5V 5k R3 10 R6 PWM 10k 0V C5 100nF 0 Figure. 4 Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 10 PAM2841 1.5A SW Current, 40V Precision WLED Driver Layout Considerations Layout Example Top Layer As for all switching power supplies, especially those in high frequency and high current ones, layout is an important design step. If layout is not carefully done, the regulator could suffer from instability as well as noise problems. (1) Use separate traces for power ground and signal ground. Power ground and signal ground are connected together to a quite ground (input connector) (2) To prevent radiation of high frequency resonance, proper layout of the high frequency switching path is essential. Minimize the length and area of all traces connecting to the SW pin. The loop including the PWM switch, schottky diode and output capacitor, contains high current rising and falling in nanosecond and thus it should be kept as short as possible. Bottom Layer (3) The input capacitor should be close to both the VIN pin and the GND pin in order to reduce the IC supply ripple. (4) Keep the signal ground traces short and as close to the IC as possible. Small signal components should be placed as close as possible to the IC, thus minimizing control signal noise interference. Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 11 PAM2841 1.5A SW Current, 40V Precision WLED Driver Ordering Information PAM2841 X X Shipping Package Type Part Number Marking Package Shipping PAM2841SR P2841 MSOP-8 3,000 units/Tape & Reel PAM2841GR EMX DFN 2x2-8 3,000 units/Tape & Reel YW Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 12 PAM2841 1.5A SW Current, 40V Precision WLED Driver Outline Dimensions MSOP-8 E HE e DETAIL A b A1 C A A2 D L L1 DETAIL A(S=3:1) REF. Millimeter REF. Millimeter Min Max Min Max A -- 1.10 L 0.40 0.70 A1 0.05 0.15 L1 A2 0.78 0.94 B 0.22 0.38 D 2.90 3.10 C 0.08 0.23 E 2.90 3.10 e HE 4.75 5.05 0.95 BSC 0.65 BSC Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 13 PAM2841 1.5A SW Current, 40V Precision WLED Driver Outline Dimensions DFN 2x2 D A B INDEX AREA (D/2 xE/2) E 4 TOP VIEW C A A1 9 8 SEATING PLANE SIDE VIEW 0.08 C e Nxb Pin#1 ID INDEX AREA (D/2 xE/2) NxL NxK E2 4 D2 BOTTOM VIEW SYMBOL A A1 Lead Pitch (e) 0.50 MIN 0.70 0.00 COMMON DIMENSION NOM MAX 0.75 0.80 0.02 0.05 Summary Table Lead Body Count Size 8 2X2 Pin #1 ID R0.20 D BSC E BSC MIN b NOM MAX MIN D2 NOM MAX MIN E2 NOM MAX MIN L NOM MAX N 2.00 2.00 0.18 0.25 0.30 1.05 1.20 1.30 0.45 0.60 0.70 0.20 0.30 0.40 8 Unit: Millimeters Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 14