PM6600 datasheet(30/43 Pages) STMICROELECTRONICS

Part #	PM6600

Description	6-row 32 mA LED driver with boost regulator for LCD panel backlight

PDF	43 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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Operation description

PM6600

30/43

The SLOPE pin allows to properly set the amount of slope compensation connecting a

simple resistor RSLOPE between the SLOPE pin and the output. The compensation ramp

starts at 35 % (typ.) of each switching period and its slope is given by the following equation:

Equation 11

Where KSLOPE, VBE = 2 V (typ.) and SE is the slope ramp in [A/s].

To avoid sub-harmonic instability, the compensating slope should be at least half the slope

of the inductor current during the off-phase for a duty-cycle greater than 50 % (i.e. at the

lowest input voltage). The value of RSLOPE can be calculated according to equation 9.

Equation 12

Figure 50.

Effect of slope compensation on small inductor current perturbation

(D > 0.5)

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

SLOPE

OUT

SLOPE

)

(

)

(

OUT

SLOPE

−

⋅

≤

TSW

Programmed inductor peak current with

slope compensation (SE)

Inductor current (CCM)

ITRIP

0.35

·TSW

∆IL

Inductor current

perturbation

PM6600 Datasheet(PDF) 30 Page - STMicroelectronics

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