-

+

PMOS_drv

Hyst Comp

FB

+

PGATE

+

-

Reference

Voltage

PGATE

R1

R2

L

LM3475

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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:

(1)

where

•

•

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,

Design Information

SETTING OUTPUT VOLTAGE

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

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