PM6600 datasheet(32/43 Pages) STMICROELECTRONICS

32 / 43 page

Operation description

PM6600

32/43

7.6

Boost current limit

The design of the external components, especially the inductor and the flywheel diode, must

be optimized in terms of size relying on the programmable peak current limit. The PM6600

improves the reliability of the final application giving the way to limit the maximum current

flowing into the critical components. A simple resistor connected between the BILIM pin and

ground sets the desired value. The voltage at the BILIM pin is internally fixed to 1.2 V and

the current limit is proportional to the current flowing through the setting resistor, according

to the following equation:

Equation 14

where

The maximum allowed current limit is 5 A, resulting in a minimum setting resistor

RBILIM > 120 kΩ. The maximum guaranteed RMS current in the power switch is 2 Arms. The

current limitation works by clamping the COMP pin voltage proportionally to RBILIM. Peak

inductor current is limited to the above threshold decreased by the slope compensation

contribution.

In a boost converter the r.m.s. current through the internal MOSFET depends on both the

input and output voltages, according to equations 15a (DCM) and 15b (CCM).

Equation 15 a

Equation 15 b

BILIM

PEAK

BOOST

⋅

rms

MOS

⋅

()

⎟

⎠

⎞

⎜

⎝

⎛

−

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⋅

−

OUT

rms

MOS

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