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FAN5609MPX Folha de dados(PDF) 7 Page - Fairchild Semiconductor |
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FAN5609MPX Folha de dados(HTML) 7 Page - Fairchild Semiconductor |
7 / 11 page PRODUCT SPECIFICATION FAN5609 REV. 1.0.2 5/30/03 7 Digital Control with PWM (Continued) A and B are PWM. ILED (Average) = δ x 20mA, where δ is Duty Cycle. (Note 3, 5) B Input (PWM) A Input (PWM) ss 1KHz ss 30% Duty Cycle 1KHz 70% Duty Cycle 70% Duty Cycle 30% Duty Cycle ss 0mA OFF ILED ILED (Average) = 0.3 x 20mA = 6mA ILED (Average) = 0.7 x 20mA = 14mA Notes: 5. Proportionally select the duty cycle to achieve a typical LED current between 1mA to 19mA. Application Information Selecting Capacitors It is important to select the appropriate capacitor types and the values for use with the FAN5609. These capacitors determine parameters such as power efficiency, maximum sustainable load current by the charge pump, input and output ripple and start-up time. In order to reduce ripple, both CIN and COUT should be low ESR capacitor. Increasing the COUT capacitor reduces the out- put ripple voltage. However this will increase the power-on time. The CIN value controls input ripple. If necessary, this ripple can be further reduced by powering the FAN5609 through a very small series inductor filter, as shown in Figure 3. Figure 3. CAP1 and CAP2 control the current capability of the charge pump and affect the overall efficiency of the system. A lower value will improve efficiency, but it may limit the LED’s currents at low input voltage. A capacitor of 100nF is opti- mal for 4 × 20 mA load over the entire input voltage range of 2.7V to 4.2V. To save space and cost, and to increase effi- ciency, this value may be reduced to 10nF for loads less than 4 x 7mA. Pulse-Width-Modulated (PWM) Mode Conversion errors are minimized and the best LED to LED matching is achieved over the entire range of average current settings, when PWM brightness control is used to modulate the LED current between zero and the maximum value (A=1, B=1). PC Board Layout For best performance, a solid ground plane is recommended on the back side of the PCB. The ground tails of CIN and COUT should be connected together close to the GND pin of IC. 100nH 0.1 µF 4.7 µF Input Power Supply VIN GND FAN5609 |
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Descrição semelhante - FAN5609MPX |
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