PAM2805 3-Modes/3W WLED Driver with 1 or 2 Cell Battery Features General Descriptio n n 3 Modes Cycling Function: The PAM2805 is a step-up DC-DC WLED driver with 3 modes cycling function(100% brightness,25% brightness and 8.5Hz blinking). Power Off <5S Power Off <5S Dimming Blinking Power Off <5S Bright The un i qu e 3 mo de s c y cl i n g fu n ct i on ca n eliminate the needs of extra functional MCU or IC. n Reset to Bright mode if Power Off time more than 5S n Adjustable Output Current: up to 750mA n 8.5Hz Blinking Mode n Low Start-Up Voltage: 0.9V(Typ.) n Low SW on Resis tanc e: 1 00mΩ n Over Temperature Protection n Over Voltage Protection n SOT23-6 Package n Pb-Free Package The PAM2805 can deliver up to 750mA output current by setting an external resistor. The PAM2805 switches at a 1.0MHz constant frequency, allowing for the use of small value external inductor and ceramic capacitors. 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 White LED Torch (Flashlight) The PAM2805 is available in SOT23-6 package. Typical Application Block Diagram VOUT 95mV Reference L V IN + A1 - V OUT 2.2 μH 10uF A2 + Rc 20uF VIN FB VOUT + Σ PAM2805 1uF PWM Logic Cc SW BLK SW VIN Comparator FB GND BLK Dimming and Blinking Logic Rs Ramp Generator 1.0MHz Oscillator PGND ILED=95mV/Rs Power Analog Microelectronics, Inc www.poweranalog.com 11/2011 Rev1.0 1 PAM2805 3-Modes/3W WLED Driver with 1 or 2 Cell Battery Pin Configuration& Marking Information Top View SOT23-6 VIN 1 GND 2 BLK 3 6 X: Internal Code Y: Year W: Weekly SW 5 VOUT 4 FB Pin Number Name Function 1 VIN 2 GND 3 BLK Connect A 1uF CAP for Blinking 4 FB Feedback 5 VOUT 6 SW Input Voltage Power Ground Output Voltage Connected to an internal NMOS switc h 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 . Storage Temperature Range......... –65 C to 150 C Lead Temperature (Soldering, 5 sec) ...........300 C Supply Voltage...............................................6V Output Voltage...............................................6V Recommended Operating Conditions Junction Temperature...............- 40 C to 125 C Operating Temperature Range .......-40 C to 85 C Thermal Information Param eter Thermal Resistance (Junction to Case) Thermal Resistance (J unction to Ambient) Internal Power Dissipation @TA=25℃ Package Sym bol Maximum SOT23-6 θJ C 130 Unit ℃/W SOT23-6 θJ A 250 SOT23-6 PD 400 mW Power Analog Microelectronics, Inc www.poweranalog.com 11/2011 Rev1.0 2 PAM2805 3-Modes/3W WLED Driver with 1 or 2 Cell Battery Electrical Characteristic TA =25 ℃ , L=2.2uH, CΙΝ =10uF, C OUT=10uF, C BLK=1uF, V F =3.4V, unless otherwise noted. Parameter Symbol Conditions Min Input Voltage Range V IN 0.9 Feedback Voltage V FB 90 VIN: 0V→3V Typ Max V F-0.2 (note 1) 95 100 Unit V mV Start-up Voltage V START Hold Voltage VHO LD Oscillator Frequenc y FO SC Over Temperature Shutdown OTS 150 ℃ Over Temperature Hysteresis OTH 30 ℃ Maximum O utput Current Range IO(M AX) Quiescent Current Switch on Resis tance IQ ILED =200mA VIN: 3V→0V ILED :750mA→100mA 0.85 V IN =2.4V ILIM VO=3.4V Current Limit Over Voltage Protection(VOUT) V OVP Blinking Frequency FBL K 0.7 V 1.0 1.15 3 2 A 4.5 7 mA Ω 0.1 CBL K=1uF MHz mA 1 Device Switching at 1MHz VO=3.4V V 750 ILED =0mA, V O=3.4V, RDS ON 0.9 8.5 V 10 Hz Note1: V F --- LED Forward Voltage Power Analog Microelectronics, Inc www.poweranalog.com 11/2011 Rev1.0 3 PAM2805 3-Modes/3W WLED Driver with 1 or 2 Cell Battery Typical Performance Characteristics TA =25 ℃ , L=2.2uH , C ΙΝ =10uF, C ΟUT =10uF, C BLK=1uF, unless otherwise noted. 1. LED Power Efficiency vs Input Voltage 2. LED Current vs Input Voltage 100 800 90 700 80 ILED=750mA( 100% brightnes s ) 600 70 60 500 50 400 40 ILED=350mA( 100% brightnes s ) 300 30 ILED=750mA(25% brightness ) 200 20 ILED=350mA ILED=750mA 10 100 ILED=350 mA(25% brightnes s ) 0 0 3.1 2.8 2.5 2.2 1.9 1.6 1.3 1.0 0.7 3.1 2.8 2.5 2.2 1. 9 1.6 1.3 1.0 0. 7 Input Volt age(V) Input Voltage(V) 3. DC Input Current vs Input Voltage 4. Feedback Voltage vs Input Voltage 2500 ILED=350mA( 100% brightness) 100 90 2000 ILED=750mA(100% br ightnes s) 80 ILED=750mA( 100% brightness) 70 1500 60 50 1000 40 ILED=350mA (25% brightnes s) 30 500 20 ILED=350mA(100% brightnes s) ILED=750 mA( 25% br ightness ) 10 0 3.4 3.1 2.8 2. 5 2.2 1.9 1.6 1.3 1. 0 0 3. 4 0.7 Input Volt age(V) 3.1 2.8 2. 5 2.2 1.9 1.6 1.3 1.0 0.7 Input Voltage(V) Power Analog Microelectronics, Inc www.poweranalog.com 11/2011 Rev1.0 4 PAM2805 3-Modes/3W WLED Driver with 1 or 2 Cell Battery Typical Performance Characteristics TA =25 ℃ , L=2.2uH , C ΙΝ =10uF, C ΟUT =10uF, C BLK=1uF, unless otherwise noted. 5. 3 Modes Change 6. Start-Up Waveform VIN VIN ILED VOUT SW IL 7. Overvoltage Protection 8. Switching Waveform VOUT VOUT IL SW IL Power Analog Microelectronics, Inc www.poweranalog.com 11/2011 Rev1.0 5 PAM2805 3-Modes/3W WLED Driver with 1 or 2 Cell Battery Application Information Inductor Selection selection is shown as follows: The PAM2805 can use small value inductors due to its switching frequency of 1 MHz. The value of inductor will focus in the range of 2.2uH to 4.7uH for most PAM2805 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 2 minimize the I R power loss, and it requires a current rating of 2A to handle the peak inductor current without saturating. Rs(Ohm)=95mV/I LED(mA) at VIN=3V. Typically, for 1W(330mA) and 3W(750mA) LED light applications, the Rs are 0.288ohm and 0.127Ohm respectively. 3 Modes Cycling T h e PA M 2 8 0 5 h a s t h r e e m o d e s : 1 0 0 % brightness, 25% brightness and blinking(typical 8.5Hz). Capacitor Selection The mode change is triggered by power on/off actions and cycles in the following sequence: bright, dimming, blinking and back to bright mode. An input capacitor is required to reduce the input ripple and noise for proper operation of the PAM2805. 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. The PAM2805 will reset to the bright mode after being power off for more than 5 seconds. Low Voltage Startup and Soft Start A minimum output capacitor value of 6.8uF is recommended under normal operating conditions, while a 10uF-22uF capacitor may be required for higher power LED current. A r e a s on a b l e v a l u e o f t h e o u tp u t c a p ac i t o r 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 PAM2805 applications. The X5R and X7R types are preferred because they maintain capacitance over wide voltage and temperature ranges. The PAM2805 has a build-in low voltage startup circuit for the best battery life solution. It can start up at 0.9V VIN typically when the preset LED current is 200mA. The soft-start function is made by clamping the output voltage of error amplifier with another voltage source which increases slowly from zero t o ne a r V IN du r i n g th e s of t- s ta r t p e r i o d . Therefore, the duty cycle of the PWM will be increased from zero to maximum in this period. The charging time of the inductor will be limited by the smaller duty so that the inrush current can be reduced to an acceptable value.` Diode Selection Over Voltage Protection It's indispensable to use a Schottky diode rated at 2A with the PAM2805. 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. SS22 is recommended Schottky diode for rectifier. The output voltage of PAM2805 is monitored by Over Voltage Protection circuit. Once VOUT goes over VOVP , typically 4.5V, the power NMOS is turned off and SW pin stops switching. Then, the VOUT is clamped to around V OVP. 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/R1. It's recommended to use a 1% or better precision resistor for the better LED current accuracy. The formula for Rs Power Analog Microelectronics, Inc www.poweranalog.com 11/2011 Rev1.0 6 PAM2805 3-Modes/3W WLED Driver with 1 or 2 Cell Battery Application Information Over Current Protection The inductor current during charging period is detected by a current sensing circuit. When the value is larger than current limiting I LIM , the power NMOS is turned off so that the inductor will be forced to leave charging stage and enter discharging stage. Therefore, the inductor peak current will not exceed I LIM , whose minimum value is 2A. PCB Layout Guidelines As for all switching power supplies, the layout and components placement of the PAM2805 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. Power Analog Microelectronics, Inc www.poweranalog.com 11/2011 Rev1.0 7 PAM2805 3-Modes/3W WLED Driver with 1 or 2 Cell Battery Ordering Information PAM2805 X X X X Number of Pins: F(6) Package Type: A Part Number Marking P ackage Type Standar d Package PAM2805AF ECXYW SOT23-6 3,000Units/Tape&Reel Power Analog Microelectronics, Inc www.poweranalog.com 11/2011 Rev1.0 8 PAM2805 3-Modes/3W WLED Driver with 1 or 2 Cell Battery Outline Dimensions θ L REF. REF. A A1 A2 c D E E1 L L1 θ b e e1 L1 (REF.) Millimeter Min Max 1.35 0.04 0.15 0.70 1.2 0.12REF. 2.70 3.10 2.60 3.00 1.40 1.80 0.45REF. 0.60REF. 0º 10º 0.30 0.50 0.95REF. 1.90REF. Power Analog Microelectronics, Inc www.poweranalog.com 11/2011 Rev1.0 9