LED7706

Operation description - boost section

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6.7

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 LED7706

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 1.23 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

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 15 a (DCM) and 15 b (CCM).

Figure 13.

Effect of slope compensation on small inductor current perturbation (D > 0.5)

Programmed inductor peak current with

Inductor current (CCM)

t

0.35

Inductor current

perturbation

BILIM

B

PEAK

,

BOOST

R

K

I

=

V

10

6

K

5

B

⋅

=