PAM2804 1A Step-Down Constant Current, High Efficiency LED Driver Features n n n n n n n n n n n n General Description The PAM2804 is a step-down constant current LED driver. When the input voltage down to lower than LED forward voltage, then PAM2804 run into LDO mode. Efficiency up to 93% 180 μA(TYP.) Quiescent Current Output Current: Up to 1A Internal Synchronous Rectifier 1.5MHz Switching Frequency Soft Start Under-Voltage Lockout Short LED Protection Open LED Protection Thermal Shutdown 5-pin Small SOT23-5 Packages Pb-Free Package The PAM2804 supports a range of input voltages from 2.5V to 6.0V, allowing the use of a single Li+/Li-polymer cell, 3AA or 4AA cell, USB, and other standard power sources. The FB voltage is only 0.1V to achieve high efficiency. PAM2804 employ internal power switch and synchronous rectifier to minimize external part count and realize high efficiency. Applications n 3AA or 4AA Batteries Powered Flashlight n 1 Cell Li-Ion Battery Powered Flashlight During shutdown, the input is disconnected from the output and the shutdown current is less than 1 μA. Other key features include under-voltage lockout to prevent deep battery discharge of the Li+ battery. . Typical Application 1 Cell Li-Ion Battery 3AA or 4AA Batteries V IN C IN 10µF L 4.7 µH VIN SW 1~5W WLED GND Co 10µF FB Rs EN ILED =0.1/Rs Power Analog Microelectronics, Inc www.poweranalog.com 10/2010 Rev1.0 1 PAM2804 1A Step-Down Constant Current, High Efficiency LED Driver Block Diagram 1.5M OSC SLOPE COMP FREQ SHIFT OSC + IAMP - VIN FB S Q R Q RS LATCH EA + VIN SWITCHING LOGIC AND BLANKING CIRCUIT MAIN SWITCH( PCH) ANTI SHOOT THRU COMP 0.6VREF EN SW SYNCHRONOUS RECTIFIER (NCH ) + IRCMP - SHUTDOWN GND Pin Configuration & Marking Information Top View SOT23 - 5 EN 1 EE: Product Code of PAM2804 X: Internal Code Y: Year W: Week 5 FB GND 2 SW 3 4 VIN Pin Description Nam e Func tion VIN Chip main power supply pin GND Ground EN Enable cont rol input. Force this pin voltage above 1. 5V, enables the chip, and below 0.3V shuts down the device. FB Feedback voltage to intern al error amplifier, the threshold voltage is 0.1V. SW The drains of t he int ernal main and synchronous p ower MOSFET. Power Analog Microelectronics, Inc www.poweranalog.com 10/2010 Rev1.0 2 PAM2804 1A Step-Down Constant Current, High Efficiency LED 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. Input Voltage..................................-0.3V to 6.5V EN, FB Pin Voltage...........................- 0.3V to VIN SW Pi n Voltage.....................-0.3V to ( V IN+0.3V ) Junction Temperature................................150°C Storage Temperature Range........-65°C to 150°C Soldering Temperature......................300°C , 5sec Recommended Operating Conditions Supply Voltage................................2.5V to 6.0V Operation Temperature Range.........-40 °C to 85 °C Junction Temperature Range........-40 °C to 125 °C Thermal Information Parameter Thermal Resistance (Junc tion to Case) Thermal Resistance (Junction to Ambient) Internal Power Dissipation Package Note SOT23-5 Symbol Maximum θJ C 130 Unit °C/W SOT23-5 θJA 250 SOT23-5 PD 400 mW Note: The maximun output current for SOT23-5 package is limited by internal power dissipation capacity as described in Application Information herein after. Power Analog Microelectronics, Inc www.poweranalog.com 10/2010 Rev1.0 3 PAM2804 1A Step-Down Constant Current, High Efficiency LED Driver Electrical Characteristic TA =25 °C , VIN =4.2V, Real WLED load, CIN =10µF, CO =10µF, L=4.7µH, unless otherwise noted. PARAMETER SYMBOL Test Conditions MIN TYP MAX UNITS 6.0 V 0.105 V Input Voltage Range VIN 2.5 Regulated Feedback Voltage V FB 0.095 Peak Induc tor Current IPK V IN=5V 1.5 A Quiescent Current IQ No load 180 µA Shutdown Current ISD V EN = 0V Oscillator Frequency Drain-Source On-State Resis tance SW Leakage Current High Effic iency 0.1 1 µA 1.5 1.8 MHz P MOSFET 0.3 0.45 Ω N MOSFET 0.35 0.5 Ω ILSW ±0.01 1 µA η 93 fOSC V O = 100% RDS (ON) IDS =100mA 1.2 % EN Threshold High V EH 1.5 V EN Threshold Low VEL EN Leakage Current IEN ±0.01 µA Over Temperature Protection OTP 150 °C OTP Hysteresis OTH 30 °C 0.3 V Power Analog Microelectronics, Inc www.poweranalog.com 10/2010 Rev1.0 4 PAM2804 1A Step-Down Constant Current, High Efficiency LED Driver Typical Performance Characteristics TA =25 °C , CIN =10μF, CO =10μF, L=4.7 μH, unless otherwise noted. Eifficiency VS Input Voltage Output Current VS Input Voltage 96% 350 94% 300 92% 250 90% 200 88% 150 86% 100 330m A 750m A 1A 84% 50 82% 3 3.5 4 4. 5 5 5.5 0 2.5 6 Rcs=0.3ohm 3 3.5 4 Input Volt age (V) 4.5 5 5.5 6 Vin(V) Output Current VS Input Voltage Output Current VS Input Voltage 0.8 1200 0.7 1000 0.6 800 0.5 600 0.4 0.3 400 0.2 200 0.1 Rcs=0.135ohm Rcs=0.1ohm 0 0 3 3.5 4 4.5 5 5.5 2.5 6 3 3.5 4 4.5 5 5.5 6 Vin(V) Input Voltage (V) Rdson VS Temperature R dson VS Input Voltage 0.4 0.6 0.35 0.5 0.3 0.4 0.25 0.3 0.2 0.2 0.15 0.1 0.1 Vin=3.6V Vin =4.2V Vin =3.6V Vin =2.7V 0 2 3 4 Input Voltage 5 6 20 70 Temperature(℃) 120 Power Analog Microelectronics, Inc www.poweranalog.com 10/2010 Rev1.0 5 PAM2804 1A Step-Down Constant Current, High Efficiency LED Driver Typical Performance Characteristics TA =25 C, CIN =10 μF, CO =10 μF, L=4.7μH, unless otherwise noted. O Quiescent Current Vs Input Voltage Start up with Enable 200 180 160 140 120 100 80 60 40 20 0 3 3.5 4 4.5 5 5.5 6 Input Voltage (V) switch on switch off Power Analog Microelectronics, Inc www.poweranalog.com 10/2010 Rev1.0 6 PAM2804 1A Step-Down Constant Current, High Efficiency LED Driver Application Information The basic PAM2804 application circuit is shown in Page 1. External component selection is determined by the load requirement, selecting L first and then Cin and Cout. temperature should be maintained below 125°C. The power dissipation is defined as: PD =IO 2 VO RDSONH + (VIN -VO )RD SONL VIN + (tSW FSIO +IQ )VIN Inductor Selection IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses. For most applications, the value of the inductor will fall in the range of 1µH to 4.7µH. Its value is chosen based on the desired ripple current. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher V IN or Vout also increases the ripple current as shown in equation 1. A reasonable starting point for setting ripple current is △I L = 400mA (40% of 1A). DIL = 1 VOUT V OUT 1 (f )(L ) V IN (1) The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. Thus, a 1.4A rated inductor should be enough for most applications (1A + 400mA). For better efficiency, choose a low DC-resis tance inductor. Using Ceramic Input and Output Capacitors Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. Using ceramic capacitors can achieve very low output ripple and small circuit size. When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage charac teristics of all the ceramics for a given value and size. Thermal consideration Thermal protection limits power dissipation in the PAM2804. When the junction temperature exceeds 150°C, the OTP (Over Temperature Protection) starts the thermal shutdown and turns the pass transistor off. The pass transistor resumes operation after the junction temperature drops below 120°C. For continuous operation, the junction Power Analog Microelectronics, Inc www.poweranalog.com 10/2010 Rev1.0 7 PAM2804 1A Step-Down Constant Current, High Efficiency LED Driver Application Information For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dis sipation reduces to: PD =IO2 RDSON H +IQ VIN As the input voltage approaches the LED forward voltage, the PAM2804 turns the P-chan nel transistor continuously on. In this mode the Voltage drop on LED is equal to the input voltage minus the voltage drop across the P - channel transistor, Inductor and current resistor: Since R DS(ON), quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. The maximum power dissipation de pend s on th e ther ma l r esi sta nc e of IC package, PCB layout, the rate of surrounding airflow and temperature difference between junction and ambient. The maximum power dissipation can be calculated by the following formula: TJ(MAX) -TA PD = θJA V LEDDROP = V IN –ILED (R dson + R L+ R S) where R dson = P-channel switch ON resistance, ILED = LED current, R L = Inductor DC resistance, R S = Inductor DC resistance. Thermal Shutdown When the die temperature exceeds 150°C, a reset occurs and the reset remains until the temperature decrease to 120°C, at which time the circuit can be restarted. Where TJ(max) is the maximum allowable junction temperature 125°C.T A is the ambient temperature and θJA is the thermal resistance from the junction to the ambient. Based on the standard JEDEC for a two layers thermal test board, the thermal resistance θJA of SOT23-5 package is 250°C/W. The maximum power dissipation at T A = 25°C can be calculated by following formula: P D =(125°C-25°C)/250°C/W=0.4W Setting the Output Current The internal feedback(FB) voltage is 0.1V (Typical). The output current is ca lculated as below: ILED=0.1/Rs The output Current is given by the following table. Rs(Ω) ILED(mA) 0.286 350 0.143 700 0.1 1000 100% Duty Cycle Operation Power Analog Microelectronics, Inc www.poweranalog.com 10/2010 Rev1.0 8 PAM2804 1A Step-Down Constant Current, High Efficiency LED Driver Application Information PCB Layout Check List When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the PAM2804. These items are also illustrated graphically in Figure 1. Check the following in your layout: 1. The power traces, consisting of the GND trace, the SW trace and the VIN trace should be kept short, direct and wide. 2. Does the V FB pin connect directly to the current sense resistor? The current sense resistor to GND trace should be kept short, direct and wide. 3. Does the (+) plate of CIN connect to VIN as closely as possible? This capacitor provides the AC current to the internal power MOSFETs. 4. Keep the switching node, SW, away from the sensitive VFB node. 5. Keep the (–) plates of C IN and C OUT as close as possible. Power Analog Microelectronics, Inc www.poweranalog.com 10/2010 Rev1.0 9 PAM2804 1A Step-Down Constant Current, High Efficiency LED Driver Ordering Information PAM 2804 X X X XXX FB Voltage Number of Pins Package Type Pin Configuration Pin Configuration A Type Package Type Number of Pins A: SOT-23 B: 5 FB Voltage 010: 0.1V 1. EN 2. GND 3. SW 4. VIN 5. FB Part Number Marking Package Type Standard Package PAM2804AAB010 Refer to P2 SOT-23-5 3,000Units/Tape&Reel Power Analog Microelectronics, Inc www.poweranalog.com 10/2010 Rev1.0 10 PAM2804 1A Step-Down Constant Current, High Efficiency LED Driver Outline Dimensions SOT23-5 D e1 θ L REF. e L1 (REF.) b REF. A A1 A2 c D E E1 L L1 θ b e e1 Millimeter Min Max 1.10 MAX 0 0.10 0.70 1 0.12 REF. 2.70 3.10 2.60 3.00 1.40 1.80 0.45 REF. 0.60 REF. 0º 10º 0.30 0.50 0.95 REF. 1.90 REF. Power Analog Microelectronics, Inc www.poweranalog.com 10/2010 Rev1.0 11