E-L6598D013TR Datasheet, PDF (9/24 Pages) STMicroelectronics – High voltage resonant controller

L6598
5
Block diagram description
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 device is provided of a soft start function. It consists in a period of time, T_SS, in which
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
,VV
,IVWDUW
,IPLQ
,RVF
JP
26&
&VV
!-V
During the soft start time the current I_SS charges the capacitor C_SS, generating a voltage
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
I_osc
=
I_fmin + (I_fstart – g_mV_Css(t))
=
I_fmin
+
⎛
⎝
I
f
sta
rt
–
g_---C-m----sI_{--ss---s-⎠⎞}
Equation 2
where
I_fmin
=
R^-V----Rf--_m^--E--_i^{-Fn- , Ifstart=}
--^V----^R----^E---^F---
R_fstart
,V _{R E F}
=
2V
Doc ID 6554 Rev 7
9/24