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LM3475 データシート(PDF) 9 Page - Texas Instruments |
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LM3475 データシート(HTML) 9 Page - Texas Instruments |
9 / 21 page - + PMOS_drv Hyst Comp FB + VOUT PGATE + - Reference Voltage VFB = 0.8V VHYST = 21 mV PGATE R1 R2 L Cff COUT VOUT = R1 + R2 R2 x VFB LM3475 www.ti.com SNVS239A – OCTOBER 2004 – REVISED JANUARY 2005 At very low or very high duty cycle operation, maximum frequency will be limited by the blanking time. The maximum operating frequency can be determined by the following equations: FMAX = D / tonmin (1) FMAX = (1-D) / toffmin where • D is the duty cycle, defined as VOUT/VIN, and tonmin • toffmin is the sum of the blanking time, the propagation delay time, and the PFET delay time (see Figure 12) (2) ENABLE PIN (EN) The LM3475 provides a shutdown function via the EN pin to disable the device. The device is active when the EN pin is pulled above 1.5V (typ) and in shutdown mode when EN is below 1.135V (typ). In shutdown mode, total quiescent current is less than 10µA. The EN pin can be directly connected to VIN for always-on operation. Design Information SETTING OUTPUT VOLTAGE The output voltage is programmed using a resistor divider between VOUT and GND as shown in Figure 13. The feedback resistors can be calculated as follows: where • Vfb is 0.8V typically (3) The feedback resistor ratio, α = (R1+R2) / R2, will also be used below to calculate output ripple and operating frequency. Figure 13. Hysteretic Window Copyright © 2004–2005, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM3475 |
同様の部品番号 - LM3475_14 |
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同様の説明 - LM3475_14 |
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