PAM2801

1W High Power White LED Driver PAM2801 F eatures 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 General Descriptio n 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. 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. The PAM2801 is available in the 6-lead SOT-23-6 package. Applications n n n n n n White LED Torch (Flashlight) White LED Camera Flash DSC(Digital Still Camera)Flash Cellular Camera Phone Flash PDA Camera Flash Camcorder Torch(Flashlight) Lamp Typical Application 2.2uH 1 Block Diagram VOUT 95mV Reference VIN SW SW 6 VIN VOUT 5 C IN + A1 - Comparator Rc Cc A2 + PWM Logic And Driver V IN 10uF OFF ON 4 PAM2801 SHDN FB 3 1W WLED CO FB Σ + - GND 2 RS 10uF Ramp Generator 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 1W High Power White LED Driver P in Configuration& Marking Information Top View SOT - 23 - 6 PAM2801 6 5 4 XX V Y W XX: Product Code V: Voltage Code Y: Year W: Weekly 1 2 3 Name SW GND FB SHDN VOUT VIN Function Switch Ground Feedback Shut Down Output Input Pin Number 1 2 3 4 5 6 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 . Input Pin Voltage...............................–0.3V to 6V SW Pin Voltage..................................–0.3V to 6V SHDN, FB Pin Voltage.........................–0.3V to 6V Operating Temperature Range .........-40 ° C to 85 ° C Storage Temperature Range......... –65 ° C to 125 ° C Lead Temperature (Soldering, 5 sec) ...........300 ° C 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 SOT-23-6 SOT-23-6 SOT-23-6 Symbol θJC θJA PD Maximum 130 ℃/W 250 400 mW Unit Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 2 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 Input Voltage Range Feedback Voltage Start-up Voltage Hold Voltage Oscillator Frequency SHDN Input High SHDN Input Low Over Temperature Shutdown Over Temperature Hysteresis Maximum Output Current Range Quiescent Current Shutdown Current Switch on Resistance Current Limit Efficiency Symbol VIN VFB VSTART VHOLD FOSC VSH VSL OTS OTH IO(MAX) IQ ISD RDSON ILIM η ILED=0mA, VO=3.4V, Device Switching at 1MHz Shutdown mode VO=3.4V VO=3.4V ILED=350mA 2 90 0.1 350 1 3 1 VIN=1.8V VIN=1.8V 150 15 ILED=243mA（RS=0.39Ω）, VIN: 0V→2.4V ILED=95mA（RS=1Ω）, VIN: 2.4V→0V 0.85 1.0 0.4 Conditions Min 0.9 90 95 0.9 0.65 1.0 1.15 Typ Max VF-0.2 (note 1) 100 Unit V mV V V MHz V V ℃ ℃ mA mA uA Ω A % PAM2801 Note1: V F - LED Forward Voltage Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 3 1W High Power White LED Driver Typical Performance Characteristics T A=25 ℃ , L=2.2uH , C ΙΝ=10uF, C Ο=10uF, unless otherwise noted. 95 PAM2801 LED Power Efficiency vs Input Voltage DC Input Current(mA) LED Power Efficiency(%) 90 85 80 75 70 65 60 55 50 3.3 3 2.7 2.4 2.1 1.8 1.5 1.2 0.9 Input Voltage(V) ILED=350mA @VF=3.4V ILED=185mA @VF=3.2V 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 3 2.7 2.4 2.1 1.8 1.5 1.2 0.9 Input Voltage(V) 400 350 LED Current(mA) LED Current vs Input Voltage LED Power Efficiency(%) 95 90 85 80 75 70 65 60 LED Power Efficiency vs LED Current VIN=3V ILED=350mA@VF=3.4V 300 250 200 150 100 3.3 3 2.7 2.4 2.1 1.8 1.5 1.2 0.9 Input Voltage(V) ILED=185mA@VF=3.2V VIN=1.8V VIN=2.4V 100 150 200 250 300 LED Current(mA) 350 400 100 Feedback Voltage vs Temperature (I LED=350mA) VIN=1.8V 100 Feedback Voltage vs Input Voltage (I LED=350mA) TA=+25℃ Feedback Voltage(mV) 90 85 80 75 70 25 50 75 Temperature(℃) 100 125 VIN=3V VIN=2.4V Feedback Voltage(V) 95 95 90 85 80 75 70 3.3 3 2.7 2.4 TA=+85℃ 2.1 1.8 1.5 1.2 0.9 Input Voltage(V) Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 4 1W High Power White LED Driver Typical Performance Characteristics (continued ) Switching Waveform Start-Up Waveform PAM2801 EN SW V OUT AC Coupling IL V OUT IL Overvoltage Protection Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 5 1W High Power White LED Driver Application Information I nductor Selection 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. 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. 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. 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. 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 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: Rs=95mV/I LED Table 1. Rs Resistor Value Selection Standard Value(Ω) 1 0.47 0.39 0.33 0.27 0.24 ILED(mA) 95 202 243 288 352 396 PAM2801 LED Dimming Control Dimming Control Using a DC Voltage to FB Pin 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. PAM2801 1W WLED FB R1 V DC 22KΩ 1KΩ RS 0.27 Ω R2 Figure 1. Dimming Control Using a DC Voltage to FB Pin Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 6 1W High Power White LED Driver Application Information (continued) Dimming Control Using a PWM Signal to FB Pin 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. SHDN PAM2801 FB I LED PAM2801 1W WLED （3a）100Hz FB 10KΩ PWM 0.1uF RS 0.27 Ω R1 22kΩ R2 1KΩ SHDN FB Figure 2. Dimming Control Using a PWM Signal to FB 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. I LED （3b）1 KHz Figure 3. Dimming Control Using a PWM Signal to SHDN Pin LED Current vs Duty Cycle 400 350 LED Current(mA) 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 1W High Power White LED Driver Application Information (continued) PCB Layout Guidelines 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 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. PAM2801 O rdering Information PAM2801 X X X X FB Voltage Number of Pins Package Type Pin Configuration Pin Configuration A Type 1. SW 2. GND 3. FB 4. SHDN 5. VOUT 6. VIN Package Type A: SOT-23-6 Number of Pins F: 6 FB Voltage 095：95mV Part Number PAM2801AAF095 Marking CDAYW Package Type SOT-23-6 Standard Package 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 1W High Power White LED Driver O utline Dimension SOT - 23 - 6 PAM2801 E1 A A e e1 E S E E VIEWS b A2 WITH PLANTING A BASE METAL SECTION A-A A1 0.25 L L1 VIEW B G A U G E P L A NE NE S E A T I N G P L ANE Symbol Spec Symbol Spec A θ A1 A2 1.10±0.2 e1 c b 0.40±0.1 L c D E 2.80±0.2 1.20±0.25 0.10±0.05 E11 1.60±0.1 e 0.95BSC 0.15±0.0.7 2.90±0.1 L1 0.60REF θ 4°±4° 1.90BSC 0.55±0.25 Power Analog Microelectronics , Inc www.poweranalog.com 08/2007 9