LM3481MMX datasheet(11/30 Pages) TI

部品番号	LM3481MMX

部品情報	LM3481/LM3481Q High Efficiency Low-Side N-Channel Controller for Switching

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LM3481

DR

ISEN

RSEN

VIN

L1

D1

Q1

COUT

VOUT

RSL

+

CSEN

Control Signal

Compensation Ramp

without RSL

-MC

VSL

'VSL

Control Signal

Compensation Ramp

with RSL

LM3481

www.ti.com

SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012

Figure 21. Additional Slope Compensation Added Using External Resistor RSL

Where,

ΔVSL = K x RSL

K = 40 µA typically and changes slightly as the switching frequency changes. Figure 23 shows the effect the

current K has on

ΔVSLand different values of RSL as the switching frequency changes.

A more general equation for the slope compensation ramp, MC, is shown below to include ΔVSL caused by the

resistor RSL.

MC = (VSL + ΔVSL) x fS

It is good design practice to only add as much slope compensation as needed to avoid subharmonic oscillation.

Additional slope compensation minimizes the influence of the sensed current in the control loop. With very large

slope compensation the control loop characteristics are similar to a voltage mode regulator which compares the

error voltage to a saw tooth waveform rather than the inductor current.

Figure 22. Increasing the Slope of the Compensation Ramp

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