LM5122ZPWPR datasheet(16/51 Pages) TI1

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OUT

SLOPE

6 x10

[V]

x R

Additional slope

ILIN u RSu10

tON

Sensed Inductor Current

9 10

ª º

VIN

LM5122

VIN

VCC

External

VCC Supply

LM5122, LM5122-Q1

SNVS954G – FEBRUARY 2013 – REVISED MAY 2016

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Product Folder Links: LM5122 LM5122-Q1

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Feature Description (continued)

Figure 19. VIN Configuration when VVIN < VVCC

7.3.3 Oscillator

The LM5122 switching frequency is programmable by a single external resistor connected between the RT pin

and the AGND pin. The resistor should be located very close to the device and connected directly to the RT pin

and AGND pin. To set a desired switching frequency (fSW), the resistor value can be calculated from Equation 4.

(4)

7.3.4 Slope Compensation

For duty cycles greater than 50%, peak current mode regulators are subject to sub-harmonic oscillation. Sub-

harmonic oscillation is normally characterized by observing alternating wide and narrow duty cycles. This sub-

harmonic oscillation can be eliminated by a technique, which adds an artificial ramp, known as slope

compensation, to the sensed inductor current.

Figure 20. Slope Compensation

The amount of slope compensation is programmable by a single resistor connected between the SLOPE pin and

the AGND pin. The amount of slope compensation can be calculated as follows:

where

•

(5)

RSLOPE value can be determined from the following equation at minimum input voltage:

LM5122ZPWPR Scheda tecnica(PDF) 16 Page - Texas Instruments