PAM2801 1W High Power White LED Driver Features General Descriptio n n LED Power Efficiency: up to 90% n LED Current Accuracy: ± 3%(V IN=3.2V to 1.1 V @V F=3.4V) n Low Start-Up Voltage: 0.9V(I LED=243mA) n Low Hold Voltage:0.65V(I LED=95mA) n Internal 2A MOSFET Switch n 1.0MHz Switching Frequency n Uses Small,Low Profile External Components n Low R DS(ON): 100mΩ (TYP.) n Open LED Protection n Over Temperature Protection n Low Profile SOT-23 Package n Pb-Free Package The PAM2801 is a step-up DC-DC converter that delivers a regulated output current. The device switches at a 1.0MHz constant frequency, allowing for the use of small value external inductor and ceramic capacitors. The PAM2801 is targeted to be used for driving 1W white LED from a 0.9V to 3.2V input. The LED current can be programmed by the external current sense resistor, Rs, connected between the feedback pin (FB) and ground. A low 95mV feedback voltage reduces the power loss in the Rs for better efficiency. With its internal 2A, 100 mΩ NMOS switch, the device can provide high efficiency even at heavy load. Applications n n n n n n LED dimming can be done by using a DC voltage applied to the FB pin and a pulse width modulation (PWM) signal applied to the FB pin or SHDN pin. During the shutdown mode, the feedback resistor Rs and the load are completely disconnected and the current consumption is reduced to less than 1uA. White LED Torch (Flashlight) White LED Camera Flash DSC(Digital Still Camera)Flash Cellular Camera Phone Flash PDA Camera Flash Camcorder Torch(Flashlight) Lamp The PAM2801 is available in the 6-lead SOT-23-6 package. Block Diagram Typical Application VOUT 2.2uH 95mV Reference 1 + A1 - SW 6 VIN VOUT 5 C IN V IN PAM2801 10uF SHDN A2 + Rc PWM Logic And Driver Cc FB 1W WLED FB 3 Σ RS + - CO OFF ON 4 GND SW VIN Comparator 10uF Ramp Generator 2 SHDN I LED=350mA,R S=0.27 Ω Shutdown And Soft-start 1.0MHz Oscillator GND Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 1 PAM2801 1W High Power White LED Driver Pin Configuration& Marking Information Top View SOT - 23 - 6 6 5 XX: Product Code V: Voltage Code Y: Year W: Weekly 4 XX V Y W 1 2 3 Pin Number Name Function 1 SW Switch 2 GND Ground 3 FB Feedback 4 SHDN Shut Down 5 VOUT Output 6 VIN Input 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 . Operating Temperature Range .........-40 ° C to 85 ° C Storage Temperature Range......... –65 ° C to 125 ° C Lead Temperature (Soldering, 5 sec) ...........300 ° C Input Pin Voltage...............................–0.3V to 6V SW Pin Voltage..................................–0.3V to 6V SHDN, FB Pin Voltage.........................–0.3V to 6V Recommended Operating Conditions Junction Temperature ............... - 40 ° C to 125 ° C Ambient Temperature .................. - 40 ° C to 85 ° C Thermal Information Parameter Thermal Resistance (Junction to Case) Thermal Resistance (Junction to Ambient) Internal Power Dissipation Package Symbol Maximum SOT-23-6 θJC 130 Unit ℃/W SOT-23-6 θJA 250 SOT-23-6 PD 400 mW Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 2 PAM2801 1W High Power White LED Driver Electrical Characteristic T A=25 ℃ , V IN=2.4V, I LED=350mA, V SHDN = V IN, L=2.2uH, C ΙΝ=10uF, C O=10uF, unless otherwise noted. Parameter Symbol Conditions Min Input Voltage Range VIN 0.9 Feedback Voltage VFB 90 ILED=243mA（RS=0.39Ω）, Start-up Voltage VSTART Hold Voltage VHOLD Oscillator Frequency FOSC SHDN Input High VSH VIN=1.8V SHDN Input Low VSL VIN=1.8V VIN: 0V→2.4V ILED=95mA（RS=1Ω）, VIN: 2.4V→0V 0.85 Typ Max VF-0.2 (note 1) 95 100 Unit V mV 0.9 V 0.65 V 1.0 1.15 1.0 MHz V 0.4 V Over Temperature Shutdown OTS 150 ℃ Over Temperature Hysteresis OTH 15 ℃ Maximum Output Current Range Quiescent Current IQ Shutdown Current ISD Switch on Resistance 350 IO(MAX) ILED=0mA, VO=3.4V, mA 1 Device Switching at 1MHz Shutdown mode RDSON VO=3.4V 0.1 Current Limit ILIM VO=3.4V Efficiency η ILED=350mA 2 3 mA 1 uA Ω A 90 % Note1: V F - LED Forward Voltage Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 3 PAM2801 1W High Power White LED Driver Typical Performance Characteristics T A=25 ℃ , L=2.2uH , C ΙΝ=10uF, C Ο=10uF, unless otherwise noted. LED Power Efficiency vs Input Voltage 90 DC Input Current(mA) LED Power Efficiency(%) 95 85 80 ILED=185mA @VF=3.2V 75 70 ILED=350mA @VF=3.4V 65 60 55 50 3.3 3 2.7 2.4 2.1 1.8 1.5 1.2 2100 1900 1700 1500 1300 1100 900 700 500 300 100 DC Input Current vs Input Voltage ILED=350mA@V F=3.4V ILED=185 mA@V F=3.2V 3.3 0.9 3 2.7 LED Current vs Input Voltage LED Power Efficiency(%) 95 LED Current(mA) 350 ILED=350mA@VF=3.4V 300 250 200 ILED=185mA@VF=3.2V 150 100 1.5 1.2 0.9 LED Power Efficiency vs LED Current VIN=3V 90 85 80 VIN=2.4V VIN=1.8V 75 70 65 3 2.7 2.4 2.1 1.8 1.5 1.2 0.9 100 150 200 250 300 LED Current(mA) Input Voltage(V) Feedback Voltage vs Temperature (I LED=350mA) 95 100 Feedback Voltage(V) Feedback Voltage(mV) 1.8 60 3.3 100 2.1 Input Voltage(V) Input Voltage(V) 400 2.4 VIN=1.8V 90 85 VIN=3V VIN=2.4V 80 75 70 350 400 Feedback Voltage vs Input Voltage (I LED=350mA) TA=+25℃ 95 90 85 TA=+85℃ 80 75 70 25 50 75 100 125 3.3 Temperature(℃) 3 2.7 2.4 2.1 1.8 1.5 1.2 0.9 Input Voltage(V) Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 4 PAM2801 1W High Power White LED Driver Typical Performance Characteristics (continued) Switching Waveform Start-Up Waveform EN SW V OUT V OUT AC Coupling IL IL Overvoltage Protection Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 5 PAM2801 1W High Power White LED Driver Application Information Inductor Selection LED current is 95mV/Rs. It's recommended to use a 1% or better precision resistor for the better LED current accuracy. The formula and table 1 for Rs selection are shown as follows: The PAM2801 can use a small value inductor due to its switching frequency of 1MHz. The value of inductor focuses in the range of 1.5uH to 4.7uH for most PAM2801 applications. In typical high current white LED applications, it is recommended to use a 4.7uH inductor. The inductor should have low DCR (DC resistance) to minimize the I 2R power loss, and it requires a current rating of 2A to handle the peak inductor current without saturating. Rs=95mV/I LED Table 1. Rs Resistor Value Selection Standard Value(Ω) ILED(mA) 1 95 0.47 202 0.39 243 0.33 288 0.27 352 0.24 396 Capacitor Selection An input capacitor is required to reduce the input ripple and noise for proper operation of the PAM2801. 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. LED Dimming Control Dimming Control Using a DC Voltage to FB Pin A minimum output capacitor value of 4.7uF is recommended under normal operating conditions, while a 10uF-22uF capacitor may be required for higher power LED current. A reasonable value of the output capacitor depends on the LED current. 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 small size of ceramic capacitors is an excellent choice for PAM2801 applications. The X5R and X7R types are preferred because they maintain capacitance over wide voltage and temperature ranges. One method for dimming the LEDs is to apply a variable DC voltage through a resistor to the FB pin of the PAM2801. The dimming control with a DC voltage is shown in the Figure1. The DC voltage artificially raises the FB pin voltage, with the DC voltage increasing, the voltage across R2 increases and the voltage across Rs decreases, which therefore lowers the LED current. The values of resistor R1 and R2 should be large enough to make the current from the DC source much smaller than the LED current while much larger than the FB leakage current. When V DC ranges from 0V to 2V, the resistors in the Figure will set the LED current from 0mA to 350mA. Diode Selection It's indispensable to use a Schottky diode rated at 2A with the PAM2801. 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. In application, the ON Semiconductor MBRA210LT3G is recommended. PAM2801 1W WLED FB R1 R2 V DC 22KΩ 1KΩ RS 0.27 Ω LED Current Setting The LED current is set by the single external Rs resistor connected to the FB pin as shown in the typical application circuit on page 1. The typical FB reference is internally regulated to 95mV. The Figure 1. Dimming Control Using a DC Voltage to FB Pin Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 6 PAM2801 1W High Power White LED Driver Application Information (continued) Dimming Control Using a PWM Signal to FB Pin SHDN By using the PWM signal to FB pin as shown in the Figure 2, the LED turns on or off and its current operates at either 0mA or the set maximum current. The PWM signal can be considered as an adjustable DC voltage. As the PWM duty cycle increases, the LED current decreases. Typically, the PWM frequency ranges from 5KHz to 40KHz. PAM2801 FB I LED （3a）100Hz 1W WLED FB 10KΩ PWM R1 R2 22kΩ 1KΩ SHDN 0.1uF FB RS 0.27 Ω Figure 2. Dimming Control Using a PWM Signal to FB Pin I LED （3b）1 KHz Figure 3. Dimming Control Using a PWM Signal to SHDN Pin Dimming Control Using a PWM Signal to SHDN Pin With the PWM signal applied to the SHDN pin of the PAM2801, the LED turns on or off. When the SHDN pin is high, the LED turn on and its current is at the set maximum current; when the SHDN pin is low, the LED turn off and its current turns to 0mA. The average LED current increase proportionally with the PWM duty cycle. A 0% duty cycle produces 0mA of LED current; a 100% duty cycle corresponds to the set maximum current. The magnitude of the PWM signal should be higher than the SHDN input high (V SH). The typical frequency of the PWM signal ranges from 100Hz to 1KHz. Figure 3 shows the LED current with the PWM duty cycle set to 50% and the PWM frequency set respectively to 100Hz and 1KHz. Figure 4 shows the LED current versus the PWM duty cycle, setting the PWM frequency to 100Hz. LED Current vs Duty Cycle 400 LED Current(mA) 350 300 250 200 150 100 50 0 0 20 40 60 80 100 Duty Cycle(%) Figure 4. LED Current vs Duty Cycle Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 7 PAM2801 1W High Power White LED Driver Application Information (continued) PCB Layout Guidelines the input pin and output pin of the IC; the inductor and schottky diode should be placed as close as possible to the switch pin by using wide and short traces for the main current path; the current sense resistor should be placed as close as possible between the ground pin and feedback pin. As for all switching power supplies, the layout and components placement of the PAM2801 is an important step in the design; especially at high peak currents and high switching frequencies. The input capacitor and output capacitor should be placed respectively as close as possible to Ordering Information PAM2801 X X X X FB Voltage Number of Pins Package Type Pin Configuration Pin Configuration A Type Package Type Number of Pins FB Voltage A: SOT-23-6 F: 6 095：95mV 1. SW 2. GND 3. FB 4. SHDN 5. VOUT 6. VIN Part Number Marking Package Type Standard Package PAM2801AAF095 CDAYW SOT-23-6 3,000Units/Tape&Reel Please consult PAM sales office or authorized Rep ./ Distributor for detailed ordering information. Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 8 PAM2801 1W High Power White LED Driver Outline Dimension A A E E1 SOT - 23 - 6 e e1 S E E VIEWS c WITH PLANTING A A2 b SECTION A-A 0.25 A1 BASE METAL G A U G E P L A NE NE S E A T I N G P L ANE L1 θ L VIEW B Symbol Spec A A1 1.20±0.25 0.10±0.05 Symbol E11 e Spec 1.60±0.1 0.95BSC A2 b 1.10±0.2 0.40±0.1 e1 L 1.90BSC 0.55±0.25 c D 0.15±0.0.7 2.90±0.1 L1 θ 0.60REF 4°±4° E 2.80±0.2 Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 9