PAM2841SR

1.5A SW Current, 40V Precision WLED Driver Features n n n n n n n n n n n PAM2841 Description 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. 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 Applications n WLED Driver System Typical Application V IN C1 10 μ F L1 22 μ H D1(SS14) PGND VIN C2 1μF SW OVP FB GND R1 910kΩ C3 1μF PAM2841 ENA Comp R2 27kΩ 10 LEDs C4 10nF R3 10Ω V IN C1 10 μ F D1(SS14) L1 22 μ H PGND VIN C2 1μF SW OVP FB GND R1 910kΩ C3 1μF PAM2841 3x9 LEDs R2 27kΩ ENA Comp R3 C4 10nF 1.1Ω Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 1 1.5A SW Current, 40V Precision WLED Driver B lock Diagram Comp OVP VIN SW PAM2841 200mV Reference FB + GM - Comparator PWM + PWM Logic And Driver Σ Ramp Generator + CS - ENA Shutdown And Soft-start 1.0MHz Oscillator GND PGND Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 2 1.5A SW Current, 40V Precision WLED Driver P in Configuration & Marking Information TOP View MSOP-8 PAM2841 1 8 2 3 4 7 6 5 XXX: Internal Code Y: Year W: Weekly DFN2X2 1 8 P2841 XXXYW EMX YW 2 3 4 7 6 5 EM: Product Code X: Internal Code Y: Year W: Weekly Pin number 1 2 3 4 5 6 7 8 Name PGND VIN ENA Comp GND FB OVP SW Power Ground Input Voltage Chip Enable, Active High Compensation Node Description Chip Ground Feedback Over Voltage Drain of Main Switch. Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 3 1.5A SW Current, 40V Precision WLED 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 . 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 Storage Temperature.....................-40 C to 150 C O Maximum Junction Temperature..................150 C O Soldering Temperature.......................300 C,5sec O O PAM2841 Recommended Operating Conditions Supply Voltage Range........................2.8V to 5.5V O O Operation Temperature Range..........-40 C to 85 C Junction Temperature Range.............0 OC to 125 OC Thermal Information Parameter Thermal Resistance (Junction to Ambient) Thermal Resistance (Junction to Case) Symbol θJA θJC Package MSOP DFN MSOP DFN Maximum 180 102 40 20 Unit °C/W °C/W °C/W °C/W Electrical Characteristic V EN=V DD=5.0V, 10 LEDs, T A=25 C , unless otherwise noted . O Parameters Supply Voltage Range Quiescent Current Shutdown Current Symbol VDD IQ ISD Test Conditions No Switching VENA=low R3=5.1Ω MIN. 2.7 TYP. 200 40 30 20 10 MAX. 5.5 300 1 UNITS V μA μA Output Current IＯ R3=6.8Ω R3=10Ω R3=20Ω VINx1.1 VENA=high ISW=100mA Switch On 0.7 Open Load Chip Shutdown Chip On VIN falling 1.2 2.0 194 mA Output Voltage Range Feedback Voltage SW On Resistance SW Current Limit SW Frequency Maximum Duty Cycle Over Voltage Protection Threshold Enable Threshold Voltage Under Voltage Lockout UVLO Hysterisis Over Temperature Shutdown Over Temperature Hysterisis VO VFB RDS(ON) ILIM fSW DC OVP VEL VEH UVLO VTH OTS OTH 40 200 0.35 1.5 1.0 95 1.2 0.4 2.2 0.2 150 30 2.4 1.3 206 0.5 V mV Ω A MHz % V V V V °C °C Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 4 1.5A SW Current, 40V Precision WLED Driver Typical Operating Characteristics T A=25 ° C,V DD=5V, unless otherwise noted . 1. Efficiency VS Input Voltage I LED=20mA, L=22 µ H 90% 85% 80% PAM2841 2. Efficiency VS Load Current 6 LED, L=22 µ H 95 % 90 % 85 % Efficiency 6LED 8LED Efficiency 75% 70% 65% 60% 55% 50% 2 3 4 Input Voltage(V) 5 80 % 75% 70% 65% 60% 10LED 12LED V DD =5V VDD=3.6V 6 0 10 20 30 40 50 60 Output Current (mA ) 3. Efficiency VS Input Voltage I LED=20mA, 10 LED 0.9 0.85 0.8 Efficiency 4. LED Current V S Output Voltage L= 47µ H 0.5 VDD=5V VDD=3V 0.4 LED Current (A) L=4.7uH L=10uH L=22uH L=33uH L=47uH 2 3 4 Input Voltage(V) 5 6 0.3 0.75 0.7 0.65 0.6 0.2 0.1 0 8 12 16 20 24 28 32 36 Output Voltage (V) Power Analog Microelectronics , Inc www.poweranalog.com 08/2008 Rev 1.3 5 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 10 LED, ILED=20mA 0.3 0.25 0.2 0.3 0.25 0.2 PAM2841 6. Feeback Voltage VS Temperature 10 LED, ILED=20mA Vfb (V) 0.15 0.1 0.05 0 2 3 4 Input Voltage (V) 5 6 Vfb(V) 0.15 0.1 0.05 0 0 20 40 60 80 100 120 140 Temperature 7. LED current VS Input voltage L=22 μ H, 10 LED 25 1.2 1 8. Frequency VS Input Voltage 10 LED 20 Frequency(Mhz) 0.8 0.6 0.4 0.2 0 ILED(mA) 15 10 R=10 R=15 R=20 0 2 3 4 Vin(V) 5 6 5 2 3 4 Input Voltage(V) 5 6 Power Analog Microelectronics , Inc www.poweranalog.com 6 08/2008 Rev 1.3 1.5A SW Current, 40V Precision WLED Driver Typical Operating Characteristics T A=25 ° C,V DD=5V, unless otherwise noted . 9. Quiescent Current VS Input Voltage 200 180 Quiescent Current (uA) PAM2841 10. Frequency VS Temperature ( 10 LED, I LED=20mA) 1.13 1.12 160 140 120 100 80 60 40 20 0 2 3 4 Input voltage (V) 5 6 Frequency(Mhz) 1.11 1.1 1.09 1.08 1.07 1.06 1.05 0 20 40 60 80 100 120 140 Temperature 11. LED Current VS Duty Cycle of PWM (PWM@EN Pin) 20 18 16 LED Current (mA) Theoretic 12. LED Current VS Duty Cycle of PWM (PWM@COMP Pin) 25 20 LED Current(mA) 14 12 10 8 6 4 2 0 0% 20% 40% f=200Hz f=100Hz 15 10 f=100HZ f=200Hz theoretic 60% 80% 100% 5 0 0% 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 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 Vin=5V,10LED,Iled=20mA PAM2841 14. Steady State Waveform 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 1.5A SW Current, 40V Precision WLED Driver A pplication Information Inductor Selection 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. 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. Schottky Diode Selection 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. 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 V RIPPLE(C)≈ 2 I OUT) 1/2*(L/(C OUT *((V OUT(MAX) -V IN(MIN) ))))*(I 2 PEAK PAM2841 to the device. 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): - 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 There are 4 different types of dimming control methods: 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. 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 1.5A SW Current, 40V Precision WLED Driver L1 VIN C1 10uF U12 1 22uH C3 1uF 1 2 3 1uF C2 4 8 7 6 5 R1 910k 2 1 D1 2 PAM2841 0 PGND VIN ENA COMP SW OV OVP FB GND 0 R2 27k PAM2841 PWM C4 10n F igure. 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. I AVE=I STATE* (T ON –T STARTUP)/(T ON+T OFF) 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