LM3488 datasheet(12/24 Pages) NSC

Part #	LM3488

Description	High Efficiency Low-Side N-Channel Controller for Switching Regulators

PDF	24 Pages

Scroll/Zoom	100%

Manufacturer	NSC [National Semiconductor (TI)]

Direct Link	http://www.national.com

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12 / 24 page

Functional Description (Continued)

The compensation ramp has been added internally in

LM3488. The slope of this compensation ramp has been

selected to satisfy most of the applications. The slope of the

internal compensation ramp depends on the frequency. This

slope can be calculated using the formula:

C =VSL.FS Volts/second

In the above equation, V

SL is the amplitude of the internal

compensation ramp. Limits for V

SL have been specified in

the electrical characteristics.

In order to provide the user additional flexibility, a patented

scheme has been implemented inside the IC to increase the

slope of the compensation ramp externally, if the need

arises. Adding a single external resistor, R

SL(as shown in

Figure 4) increases the slope of the compensation ramp, M

by :

In this equation,

∆V

SL is equal to 40.10

-6R

SL. Hence,

∆V

SL versus RSL has been plotted in Figure 5 for different

frequencies.

10138811

FIGURE 3. Compensation Ramp Avoids Sub-Harmonic Oscillation

LM3488 Datasheet(PDF) 12 Page - National Semiconductor (TI)