PAM2841EV1 User Guide 1.5A SW CURRENT, 40V PRECISION WLED DRIVER General Description The PAM2841 is a step-up current mode LED Driver. The PAM2841 supports a range of input voltages from 2.5V to 5.5V, allowing the use of a single Li+/Li- polymer cell, 3AA cell battery, USB, and other standalone power sources. PAM2841 employs internal power switch to minimize external components count and yield a high efficiency (~80%). A bill of material, schematics, and layout are included that describes the parts used on this demonstration board along with measured performance characteristics. These materials can be used as a reference design. PAM2841EV1 Specifications Parameter Value Input Voltage LED Current Number of LEDs XYZ Dimension 2.5 to 5.5VDC 20mA (Adjustable) 10 2.2” x 1.1” x 0.4” Evaluation Board DC+ LED+ DCLEDFigure 1: Top View Key Features Capable of Driving 10 or More WLEDs Chip Enable with Soft-Start Analog and PWM Dimming Efficiency up to 80% Low Quiescent Current 1MHz Fixed Frequency Under-Voltage Lockout Open/Short Protection Thermal Shutdown DC+ LED+ DCLEDFigure 2: Bottom View Connection Instructions Input Voltage: 2.5 to 5.5VDC (DC+, DC-) LED Outputs: LED+ (Black), LED- (White) Applications WLED Driver System PAM2841EV1 Rev1 February 2015 www.diodes.com Page 1 of 6 PAM2841EV1 User Guide 1.5A SW CURRENT, 40V PRECISION WLED DRIVER Evaluation Board Schematic Figure 3: Evaluation Board Schematic Evaluation Board Layout Figure 4: PCB Layout Top View Figure 5: PCB Layout Bottom View Quick Start Guide 1. 2. 3. 4. 5. 6. By default, the evaluation board is preset at 20mA LED Current by R3 (10 Ohm). Ensure that the DC source is switched OFF or disconnected. Connect the 2.5 to 5.5VDC DC line wires of power supply to DC+ and DC- on the board. Connect the anode wire of external LED string to LED+ output test point. Connect the cathode wire of external LED string to LED- output test point. Turn on the main switch. LED string should light up. PAM2841EV1 Rev1 February 2015 www.diodes.com Page 2 of 6 PAM2841EV1 User Guide 1.5A SW CURRENT, 40V PRECISION WLED DRIVER Bill of Material # 1 2 3 4 5 6 7 8 9 10 11 12 13 Name IC1 C1 C2 C3 C4 C5 R1 R2 R3 R4 L1 D1 PCB Quantity 1 1 1 1 1 1 1 1 1 1 1 1 1 Part number PAM2841 GRM21R71C106B GRM21R71C105B GRM21R71C105B GRM21R71C103B GRM21R71C102B RC0805JR-07910KL RC0805JR-0727KL RC0805JR-0710RL RC0805JR-072KL LQH32CN220K ES11QS04 PAM2841 EB7CFA Manufacturer Diodes Inc Murata Murata Murata Murata Murata Yageo Yageo Yageo Yageo Description LED Driver MSOP-8 10µF Cer Cap 10V 10% X5R 1210 1µF Cer Cap 10V 10% X5R 0805 1µF Cer Cap 50V 10% X5R 1210 10nF Cer Cap 10V 10% X5R 0805 1nF Cer Cap 10V 10% X5R 0805 Murata Nihon 22µH, 1A Inductor 1210 1A Schottky diode 1210 SMD 910kΩ Resistor 1/8W 5% 0805 SMD 27kΩ Resistor 1/8W 5% 0805 SMD 10Ω Resistor 1/8W 1% 0805 SMD 2kΩ Resistor 1/8W 5% 0805 SMD Functional Performance (10 LEDs @20mA) Vin (DC) 2.5 3 3.5 4 4.5 5 5.5 Pin (W) 0.888 0.753 0.717 0.701 0.683 0.682 0.685 PAM2841EV1 Rev1 February 2015 www.diodes.com V_out (V) 26.76 26.76 26.76 26.76 26.76 26.76 26.76 I_out (mA) 19.84 19.66 19.97 19.99 20.05 20.05 20.16 P_out (W) 0.531 0.526 0.534 0.535 0.537 0.537 0.540 Efficiency (%) 59.80 69.86 74.52 76.31 78.56 78.67 78.79 # of LEDs 10 Page 3 of 6 PAM2841EV1 User Guide 1.5A SW CURRENT, 40V PRECISION WLED DRIVER Iout (mA) vs Input Voltage Vin=2.5-5.5VDC; OUT=10 LEDs 26 Efficiency(%) vs Input Voltage PAM2841 Efficiency (%) 24 Iout (mA) Vin=2.5-5.5VDC; OUT=10 LEDs 100 22 20 18 PAM2841 90 80 70 60 50 16 2 3 4 5 6 Input Voltage (VDC) Figure 6 Vin (DC) vs. Iout (mA) 2 3 4 5 Input Voltage (VDC) Figure 7 Vin (DC) vs. Efficiency (%) Application Information Setting the Output Current: The internal feedback (FB) voltage is 0.2V (Typical). The output current is calculated as below: ILED = 0.2/R3 The output Current is given by the following table. R3(Ω) ILED (mA) 10 6.8 5.1 20 30 40 As the input voltage approaches the LED forward voltage, the PAM2841 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 +150°C, a reset occurs and the reset remains until the temperature decrease to +120°C, at which time the circuit can be restarted. PAM2841EV1 Rev1 February 2015 www.diodes.com Page 4 of 6 6 PAM2841EV1 User Guide 1.5A SW CURRENT, 40V PRECISION WLED DRIVER PCB Layout Guidelines Decoupling Capacitors (1) The capacitors (C2) need to place very close to the PAM2841’s pins. Grounding (1) The decoupling capacitors C2, C4 should each to be grounded to analog ground AGND; (2) The capacitors C1, C3, R2 and R3 should each be grounded to power ground PGND; (3) Connect the AGND and PGND islands by connecting the GND pins directly to the exposed backside pad. Make no other connections between these separate ground planes. Others (1) Connect L1, SW, D1, C3 with short and wide connections; (2) Place the OVP voltage setting-divider resistors (R1, R2) as close to the OV pin as possible. The divider’s center trace should be kept short; (3) Minimize the size of the SW node while keeping it wide and short. Keep the SW node away from the feedback node and ground; (4) Place the FB resistor (R3) as close to the FB pin as possible. PAM2841EV1 Rev1 February 2015 www.diodes.com Page 5 of 6 PAM2841EV1 User Guide 1.5A SW CURRENT, 40V PRECISION WLED DRIVER 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). Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or trademark rights, nor the rights of others. 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