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LX1664 Datasheet(PDF) 11 Page - Microsemi Corporation |
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LX1664 Datasheet(HTML) 11 Page - Microsemi Corporation |
11 / 17 page DUAL OUTPUT PWM CONTROLLERS WITH 5-BIT DAC LX1664/1664A, LX1665/65A PRODUCT DA T ABOOK 1996/1997 11 Copyright © 1999 Rev. 1.2 11/99 P RODUCTION D ATA S HEET BILL OF MATERIALS C 1 1500µF, 6.3V capacitor MV-GX Sanyo 4 C 2 1500µF, 6.3V capacitor MV-GX Sanyo 2 C 7, C9 330µF, Electrolytic MV-GX Sanyo 2 C 3 0.1µF SMD Cap 1 C 4 390pF SMD Cap 1 C 8 680pF SMD Cap 1 C 5 1µF, 16V SMD Ceramic 1 L 1 2.5µH Inductor HM0096832 BI or equivalent 1 L 2 1µH Inductor 1 Q 1 MOSFET IRL3102 International Rectifier or equivalent 1 Q 2 MOSFET IRL3303 International Rectifier or equivalent 1 Q 3 MOSFET IRLZ44 International Rectifier or equivalent 1 R 5, R6 Resistor (See Table 6 for values) SMD Resistor 2 R 1 2.5mΩ Sense Resistor IRC OARS-1 or PCB trace 1 U1 Controller IC LX1665CDW Linfinity 1 Total 21 Ref Description Part Number / Manufacturer Qty. LX1665 Bill of Materials (Refer to Product Highlight) USING THE LX1664/65 DEVICES The LX1664/65 devices are very easy to design with, requiring only a few simple calculations to implement a given design. The following procedures and considerations should provide effec- tive operation for virtually all applications. Refer to the Appli- cation Information section for component reference designa- tors. TIMING CAPACITOR SELECTION The frequency of operation of the LX166x is a function of duty cycle and OFF-time. The OFF-time is proportional to the timing capacitor (which is shown as C 8 in all application schematics in this data sheet), and is modulated to minimize frequency variations with duty cycle. The frequency is constant, during steady-state operation, due to the modulation of the OFF-time. The timing capacitor (C T) should be selected using the following equation: C T = Where I DIS is fixed at 200µA and fS is the switching frequency (recommended to be around 200kHz for optimal operation and component selection). When using a 5V input voltage, the switching frequency (f S) can be approximated as follows: C T = 0.621 * Choosing a 680pF capacitor will result in an operating frequency of 183kHz at V OUT = 2.8V. When a 12V power input is used, he capacitor value must be changed (the optimal timing capacitor for 12V input will be in the range of 1000-1500pF). L 1 OUTPUT INDUCTOR SELECTION The inductance value chosen determines the ripple current present at the output of the power supply. Size the inductance to allow a nominal ±10% swing above and below the nominal DC load current, using the equation L = V L * ∆T/∆I, where ∆T is the OFF-time, V L is the voltage across the inductor during the OFF- time, and ∆I is peak-to-peak ripple current in the inductor. Be sure to select a high-frequency core material which can handle the DC current, such as 3C8, which is sized for the correct power level. Typical inductance values can range from 2 to 10µH. Note that ripple current will increase with a smaller inductor. Exceeding the ripple current rating of the capacitors could cause reliability problems. (1 - V OUT /VIN ) * IDIS f S (1.52 - 0.29 * VOUT ) I DIS f S |
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