L6598

Block diagram description

Doc ID 6554 Rev 7

9/24

5

Block diagram description

5.1

High/low side driving section

An high and low side driving section provide the proper driving to the external power MOS or

IGBT. An high sink/source driving current (450/250 mA typ) ensure fast switching times also

when size for power MOS are used. The internal logic ensures a minimum dead time to

avoid cross-conduction of the power devices.

5.2

Timing and oscillator section

the switching frequency shifts from fstart to fmin. This feature is explained in the following

description (ref. fig.7 and fig.8).

Figure 6.

Soft start and frequency shifting block

ramp which is delivered to a transconductance amplifier, as shown in fig. 7. Thus this

voltage signal is converted in a growing current which is subtracted to Ifstart. Therefore the

current which drives the oscillator to set the frequency during the soft start is equal to:

Equation 1

Equation 2

I

osc

I

fmin

I

fstart

g

()

–

()

+

I

fmin

I

fstart

g

C

ss

--------------

–

⎝⎠

⎛⎞

+

==

where

I

fmin

V

REF

R

fmin

-------------- I

fstart

V

REF

R

fstart

---------------- V

REF

2V

=

,

=

,

=