LM3519MKEV

User's Guide SNVA126A – February 2006 – Revised April 2013 AN-1406 LM3519 Evaluation Board 1 General Description The LM3519 evaluation board is a working demonstration of a step up DC-DC converter. The LM3519 drives up to four white LEDs with a constant current to provide LCD backlighting in handheld devices. The LED current is internally set to 20 mA eliminating the use of external resistor. The series connection allows the LED current to be identical for uniform brightness and minimizes the number of traces to the LEDs. Brightness control is achieved by applying a PWM signal on the En pin with frequencies up to 30 kHz. A proprietary PFM architecture implementation results in non pulse skipping variable frequency operation over input voltage range permitting the use of low-cost, small external components. For further information and electrical characteristics, see the LM3519 High Frequency Boost White LED Driver with High-Speed PWM Brightness Control Data Sheet (SNVS394). 2 Operating Conditions • • • • • 3 Junction temperature (TJ) range: -40°C to +125°C Ambient temperature (TA) range: -40°C to +85°C Input Voltage Range: 2.7 V to 5.5 V IOUT = 20 mA Package SOT 23 - 6 pin Typical Application Figure 1. Typical Application Circuit All trademarks are the property of their respective owners. SNVA126A – February 2006 – Revised April 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated AN-1406 LM3519 Evaluation Board 1 Connection Diagram and Package Information 4 www.ti.com Connection Diagram and Package Information Figure 2. SOT23-6, Top View Table 1. Pin Descriptions (SOT23-6) 5 Pin No Name Description 1 En Device Enable Connection 2 Gnd Ground Connection 3 VOUT Output Voltage Connection 4 LED_rtn White LED Current Sensing Input Connection 5 Sw Drain Connection of the Internal Power Field Effect Transistor (FET) Switch 6 VIN Input or Supply Voltage Connection PWM Dimming If a pulse width modulation (PWM) signal is used to adjust the brightness, a control signal frequency between 17 kHz to 30 kHz is recommended. Although the LM3519 is capable of operating outside this frequency range, it is not recommended to operate below 17 kHz for the following reasons: • Frequency below 100Hz is likely to cause visible flicker in the light emitted by the LED string • Frequency below 17 kHz may induce audible noise due to combinations of some capacitance and PCB A PWM frequency above 30 kHz is possible but the current linearity vs duty cycle will be affected. If it is not possible to operate the dimming control above 17 kHz, audible noise emission can be minimized by using capacitors with low susceptibility to piezoelectric induced stresses, such as poly film designs. Minimum audible noise is most likely to occur when the PWM frequency is less than 2 kHz. It is recommended that any application using a PWM control signal below 17 kHz be thoroughly evaluated for undesirable audible noise. 6 Layout Guidelines The input capacitor, CIN, must be placed close to the LM3519. Placing CIN close to the device will reduce the metal trace resistance effect on input voltage ripple. Metal trace connections for the COUT capacitor can increase the effective series resistance, which affects output voltage ripple and efficiency. Trace connections to the inductor should be short and wide to reduce power dissipation, increase overall efficiency and reduce EMI radiation. The diode, like the inductor, should have trace connections that are short and wide to reduce power dissipation and increase overall efficiency. For more details regarding layout guidelines for switching regulators, see AN-1149 Layout Guidelines for Switching Power Supplies (SNVA021). 2 AN-1406 LM3519 Evaluation Board SNVA126A – February 2006 – Revised April 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated Evaluation Board Layout www.ti.com 7 Evaluation Board Layout Figure 3. Top Layer Figure 4. Bottom Layer SNVA126A – February 2006 – Revised April 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated AN-1406 LM3519 Evaluation Board 3 Evaluation Board Layout www.ti.com Table 2. Bill of Materials (BOM) For Common Configurations Component Name Value Manufacturer U1 LM3519 SOT23-6 Texas Instruments Cin 4.7 uF, 6.3 V, 0603 AVX06033D475MAT AVX Cout 1 µF, 25 V, 0603 AVX06033D105MAT AVX D1 Schottky Diode CMMSH1-40 Central Semiconductor L1 2.2 µH LPO3310-222ML CoilCraft LED1-4 LWT67C Hyper Topled Osram Opto Semiconductors Test Pin 4 Specification Description Size Quantity VIN Turret 0.09in 1 GND Turret 0.09in 1 EN Turret 0.09in 1 SW Turret 0.09in 1 VOUT Turret 0.09in 1 AN-1406 LM3519 Evaluation Board SNVA126A – February 2006 – Revised April 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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