LM3488MM datasheet(13/37 Pages) TI1

13 / 37 page

MC =

40x10

-6 . R

RSEN

Amps

second

LM3488, LM3488-Q1

www.ti.com

SNVS089N – JULY 2000 – REVISED DECEMBER 2014

Feature Description (continued)

With the compensation ramp,

(2)

Figure 21. Sub-Harmonic Oscillation for D>0.5

Figure 22. Compensation Ramp Avoids Sub-Harmonic Oscillation

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:

MC = VSL.FS Volts/second

(3)

In the above equation, VSL is the amplitude of the internal compensation ramp. Limits for VSL 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,

RSL(as shown in Figure 23) increases the slope of the compensation ramp, MC by :

(4)

In this equation,

ΔVSL is equal to 40.10

-6R

SL. Hence,

(5)

ΔVSL versus RSL has been plotted in Figure 24 for different frequencies.

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LM3488MM Datasheet(PDF) 13 Page - Texas Instruments