LM3409EVAL/NOPB

User's Guide SNVA391D – May 2009 – Revised May 2013 AN-1954 LM3409 Demonstration Board 1 Introduction This demonstration board showcases the LM3409 PFET controller for a buck current regulator. It is designed to drive 4 LEDs (VO = 15V) at a maximum average LED current (ILED = 1A) from a DC input voltage (VIN = 24V). The switching frequency (fSW = 525 kHz) is targeted for the nominal operating point, however fSW varies across the entire operating range. The circuit can accept an input voltage of 6V-42V. However, if the input voltage drops below the regulated LED string voltage, the converter goes into dropout and VO = VIN ideally. The PCB is made using 2 layers of 2 oz. copper with FR4 dielectric. The board showcases several features of the LM3409 including both analog dimming using a potentiometer (R5) tied to the IADJ pin and internal PWM dimming using the EN pin. There is a header (J1) with a removable jumper, which is used to select PWM dimming or low power shutdown. The board has a right angle connector (J2) which can mate with an external LED load board allowing for the LEDs to be mounted close to the driver. This reduces potential ringing when there is no output capacitor. Alternatively, the LED+ and LED- turrets can be used to connect the LED load. This board can be easily modified to demonstrate other operating points as shown in Section 8. The LM3409 / LM3409HV / LM3409Q / LM3409QHV / LM3409N PFET Buck Controller for High Power LED Drivers (SNVS602) data sheet's Design Procedure can be used to design for any set of specifications. 100 EFFICIENCY (%) 95 90 85 80 75 15 20 25 30 35 40 45 INPUT VOLTAGE (V) Figure 1. Efficiency with 4 Series LEDS AT 1A All trademarks are the property of their respective owners. SNVA391D – May 2009 – Revised May 2013 Submit Documentation Feedback AN-1954 LM3409 Demonstration Board Copyright © 2009–2013, Texas Instruments Incorporated 1 Schematic 2 www.ti.com Schematic R3 U1 R2 1 VIN UVLO 10 VADJ 2 VIN C4 VCC IADJ C1 C2 9 GND LED+ R5 C6 3 J1 R1 LM3409 EN CSP 8 J2 R4 4 COFF CSN C3 7 DAP 5 GND PGATE 6 1 14 2 13 3 12 5 10 6 9 7 8 Q1 L1 C5 D1 LEDFigure 2. Board Schematic 3 2 Pin Descriptions Pin(s) Name Description 1 UVLO Input under-voltage lockout Connect to a resistor divider from VIN and GND. Turn-on threshold is 1.24V and hysteresis for turn-off is provided by a 22µA current source. 2 IADJ Analog LED current adjust Apply a voltage between 0 - 1.24V, connect a resistor to GND, or leave open to set the current sense threshold voltage. 3 EN Logic level enable 4 COFF Off-time programming 5 GND Ground 6 PGATE Gate drive 7 CSN Negative current sense Connect to the negative side of the sense resistor. 8 CSP Positive current sense Connect to the positive side of the sense resistor (VIN). 9 VCC VIN- referenced linear regulator output 10 VIN Input voltage DAP DAP Thermal pad on bottom of IC Application Information Apply a voltage >1.74V to enable device, a PWM signal to dim, or a voltage