L6388ED(2015) Просмотр технического описания (PDF) - STMicroelectronics

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L6388ED
(Rev.:2015)

High voltage high and low-side driver

STMicroelectronics 

Bootstrap driver

L6388E

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

Equation 2

Vdrop = Ich argeRdson  Vdrop = T---Q-c---h-g--a-a--r-t-ge---e-Rdson

where Qgate is the gate charge of the external power MOSFET, RDS(on) is the on-resistance

of the bootstrap DMOS, and Tcharge is the charging time of the bootstrap capacitor.

For example: using a power MOSFET with a total gate charge of 30 nC, the drop on the

bootstrap DMOS is about 1 V, if the Tcharge is 5 s.

In fact:

Equation 3

Vdrop = -3--5-0----n--s-C---  125  0.8V

Vdrop should be taken into account when the voltage drop on CBOOT is calculated: if this drop

is too high, or the circuit topology doesn’t allow a sufficient charging time, an external diode

can be used.

Figure 5. Bootstrap driver

DBOOT

VS

VBOOT

H.V.

HVG

VOUT

CBOOT

TO LOAD

LVG

a

VS

VBOOT

H.V.

HVG

VOUT

CBOOT

TO LOAD

LVG

b

10/18

DocID13991 Rev 5

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