DocID024048 Rev 2

11/16

L6395

Bootstrap driver

16

7

Bootstrap driver

A bootstrap circuitry is needed to supply the high voltage section. This function is normally

accomplished using a high voltage fast recovery diode (Figure 6). In the L6395 device

a patented integrated structure replaces the external diode. It is implemented using a high

voltage DMOS, driven synchronously with the low-side driver (LVG), with a diode in series,

as shown in Figure 7. An internal charge pump provides the DMOS driving voltage.

Equation 1

loss.

It must be:

Equation 2

300 mV.

account also the leakage and quiescent losses.

E.g.: HVG steady state consumption is lower than 220

must supply 1.1

The internal bootstrap driver offers some important advantages: the external fast recovery

diode can be avoided (it usually has a high leakage current).

fulfilled and it has to be long enough to charge the capacitor.

120

). At low switching frequency, this drop can be neglected but, operating at high

switching frequency, it should be taken into account.

The following equation is useful to compute the drop on the bootstrap DMOS:

Equation 3

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

=

»

arg



arg





=





=