L6388E Просмотр технического описания (PDF) - STMicroelectronics

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L6388E

High-voltage high and low side driver

STMicroelectronics 

L6388E

Bootstrap driver

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

Vdrop

=

Ich arg eRdson → Vdrop

=

---Q-----g---a---t-e----

Tch arge

Rd

so

n

where Qgate is the gate charge of the external power MOS, Rdson is the on resistance of the

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

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

DMOS is about 1V, if the Tcharge is 5µs. In fact:

Vdrop = -3--5-0--µ--n--s-C--- ⋅ 125Ω ∼ 0.8V

Vdrop has to 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.

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