PAM2804 1A STEP-DOWN CONSTANT CURRENT, HIGH EFFICIENCY LED DRIVER Description Pin Assignments The PAM2804 is a step-down constant current LED driver. When the Top View TSOT25 input voltage is down to lower than LED forward voltage, then PAM2804 goes into LDO mode. 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 employs internal power switch and synchronous rectifier to minimize external part count and realize high efficiency. Applications During shutdown, the input is disconnected from the output and the shutdown current is less than 1A. Other key features include undervoltage lockout to prevent deep battery discharge of the Li+ battery. 3AA or 4AA Batteries Powered Flashlight 1 Cell Li-Ion Battery Powered Flashlight Features Efficiency up to 93% 180A(typ) Quiescent Current Output Current: Up to 1A Internal Synchronous Rectifier 1.5MHz Switching Frequency Soft-Start Undervoltage Lockout Short LED Protection Open LED Protection Thermal Shutdown 5-Pin Small TSOT25 Packages Pb-Free Package Typical Applications Circuit ILED = 0.1/RS PAM2804 Document number: DS36403 Rev. 3 - 2 1 of 10 www.diodes.com September 2015 (c) Diodes Incorporated PAM2804 Pin Description Pin Number Pin Name 1 EN 2 3 4 GND Enable control input. Force this pin voltage above 1.5V, enables the chip, and below 0.3V shuts down the device. Ground SW The drains of the internal main and synchronous power MOSFET. VIN Chip main power supply pin. 5 FB Feedback voltage to internal error amplifier, the threshold voltage is 0.1V. Function Block Diagram Absolute Maximum Ratings (@TA = +25C, unless otherwise specified.) 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. Parameter Input Pin Voltage Rating -0.3 to +6.5 Unit EN, FB Pin Voltage -0.3 to VIN V SW Pin Voltage Junction Temperature Range Storage Temperature Range Soldering Temperature PAM2804 Document number: DS36403 Rev. 3 - 2 -0.3 to (VIN +0.3) 150 -65 to +150 +300, 5sec C 2 of 10 www.diodes.com September 2015 (c) Diodes Incorporated PAM2804 Recommended Operating Conditions (@TA = +25C, unless otherwise specified.) Parameter Rating Supply Voltage 2.5 to 6.0 Operation Temperature Range -40 to +85 Junction Temperature Range -40 to +125 Unit C Thermal Information Parameter Symbol Package Max Thermal Resistance (Junction to Case) JC TSOT25 (Note 1) 130 Thermal Resistance (Junction to Ambient) JA TSOT25 250 Internal Power Dissipation PD TSOT25 400 Note: Unit C/W mW 1. The maximum output current for TSOT25 package is limited by internal power dissipation capacity as described in Application Information herein after. Electrical Characteristics (@TA = +25C, VIN = 4.2V, Real WLED load, L = 4.7H, CIN = 10F, CO = 10F, unless otherwise specified.) Min Typ Max Units Input Voltage Range Parameter VIN - 2.5 - 6.0 V Regulated Feedback Voltage VFB - 0.095 0.100 0.105 V Peak Inductor Current IPK - 1.5 - A Quiescent Current IQ VIN = 5V No Load - 180 - A Shutdown Current ISD VEN = 0V - - 1 A Oscillator Frequency fOSC VO = 100% Drain-Source On-State Resistance SW Leakage Current Symbol RDS(ON) Test Conditions IDS = 100mA P MOSFET N MOSFET 1.2 1.5 1.8 MHz - 0.30 0.35 0.45 0.50 ILSW - - 0.01 1 A High Efficiency - - 93 - % EN Threshold High VEH - 1.5 - - V EN Threshold Low VEL - - - 0.3 V EN Leakage Current IEN OTP OTH - - 0.01 - A - - +150 +30 - C C Over-Temperature Protection OTP Hysteresis PAM2804 Document number: DS36403 Rev. 3 - 2 3 of 10 www.diodes.com September 2015 (c) Diodes Incorporated PAM2804 Typical Performance Characteristics (@TA = +25C, L = 4.7F, CIN = 10F, CO = 10F, unless otherwise specified.) PAM2804 Document number: DS36403 Rev. 3 - 2 4 of 10 www.diodes.com September 2015 (c) Diodes Incorporated PAM2804 Typical Performance Characteristics (cont.) @TA = +25C, L = 4.7F, CIN = 10F, CO = 10F, unless otherwise specified.) Start up with Enable PAM2804 Document number: DS36403 Rev. 3 - 2 PWM Dimming: ILED vs. Duty Cycle 5 of 10 www.diodes.com September 2015 (c) Diodes Incorporated PAM2804 Application Information PWM Dimming The PAM2804 can be used to dim LED current dimming by driving the EN pin via PWM waveform. The SW pin current is then effectively switched on and off causing the LED current to turn on and off. The recommended PWM frequency is 500Hz (see Figure on page 5 for details). Inductor Selection 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. For most applications, the value of the inductor will fall within the range of 1H to 4.7H. 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 VIN or VOUT also increases the ripple current as shown in equation 1. A reasonable starting point for setting ripple current is IL = 400mA (40% of 1A). IL 1 VOUT VOUT 1 f L VIN Equation (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-resistance inductor. Using Ceramic Input 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 characteristics 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 +150C, the OTP (Overtemperature Protection) starts the thermal shutdown and turns the pass transistor off. The pass transistor resumes operation after the junction temperature drops below +120C. For continuous operation, the junction temperature should be maintained below +125C. The power dissipation is defined as: PD IO2 VO RDS(ON )H VIN VORDS(ON )L VIN tSW FSIO IQ VIN IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses. For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: PD IO2 RDS(ON)H IQ VIN PAM2804 Document number: DS36403 Rev. 3 - 2 6 of 10 www.diodes.com September 2015 (c) Diodes Incorporated PAM2804 Application Information (cont.) Since RDS(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 depends on the thermal resistance 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: PD TJ(MAX ) T A JA Where TJ(MAX) is the maximum allowable junction temperature +125C. TA is the ambient temperature and JA 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 JA of TSOT25 package is 250C/W. The maximum power dissipation at TA = +25C can be calculated by following formula: P 125C 25C / 250C / W 0.4W D Setting the Output Current The internal feedback (FB) voltage is 0.1V (Typical). The output current is calculated as below: ILED 0.1/ RS The output Current is given by the following table. RS() ILED(mA) 0.286 350 0.143 700 0.1 1,000 As the input voltage approaches the LED forward voltage, the PAM2804 turns the P-Channel 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: VLEDDROP VIN ILED RDS(ON) RL RS Where RDS(ON) = P-Channel switch ON resistance, ILED = LED current, RL = Inductor DC Resistance, RS = Inductor DC Resistance. Thermal Shutdown When the die temperature exceeds +150C, a reset occurs and the reset remains until the temperature decrease to +120C, at which time the circuit can be restarted. 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 VFB 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 CIN and COUT as close as possible. PAM2804 Document number: DS36403 Rev. 3 - 2 7 of 10 www.diodes.com September 2015 (c) Diodes Incorporated PAM2804 Ordering Information PAM2804 X X X xxx Pin Configuration A Type: 1. EN 2. GND 3. SW 4. VIN 5. FB Part Number PAM2804AAB010 Package Type Number of Pins A: TSOT25 B: 5 Marking Refer to Marking Information Below FB Voltage 010: 0.1V Package Type Standard Package TSOT25 3,000 Units/Tape & Reel Marking Information Top View TSOT25 PAM2804 Document number: DS36403 Rev. 3 - 2 8 of 10 www.diodes.com September 2015 (c) Diodes Incorporated PAM2804 Package Outline Dimensions TSOT25 D e1 01(4x) E1/2 E/2 E1 c E Gauge Plane 0 L 01(4x) b e A2 A1 A Seating Plane L2 Seating Plane TSOT25 Dim Min Max Typ A - 1.00 A1 0.01 0.10 A2 0.84 0.90 b 0.30 0.45 c 0.12 0.20 D 2.90 E 2.80 E1 1.60 e 0.95 BSC e1 1.90 BSC L 0.30 0.50 L2 0.25 BSC 0 8 4 1 4 12 All Dimensions in mm Suggested Pad Layout TSOT25 C Dimensions Value (in mm) C 0.950 X 0.700 Y 1.000 Y1 3.199 Y1 Y X PAM2804 Document number: DS36403 Rev. 3 - 2 9 of 10 www.diodes.com September 2015 (c) Diodes Incorporated PAM2804 IMPORTANT NOTICE DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION). 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Copyright (c) 2015, Diodes Incorporated www.diodes.com PAM2804 Document number: DS36403 Rev. 3 - 2 10 of 10 www.diodes.com September 2015 (c) Diodes Incorporated Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Diodes Incorporated: PAM2804AAB010