L6385 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

MFG CO.

L6385

HIGH-VOLTAGE HIGH AND LOW SIDE DRIVER

STMicroelectronics 

1 2 3 4 5 6 7 8 9

L6385

Figure 1. Input/Output Timing Diagram

HIN

HVG

LIN

LVG

D99IN1053

Figure 2. Typical Rise and Fall Times vs.

Load Capacitance

time

(nsec)

D99IN1054

250

200

Tr

150

Tf

100

50

0

0

1

2

3

4

5 C (nF)

For both high and low side buffers @25˚C Tamb

BOOTSTRAP DRIVER

A bootstrap circuitry is needed to supply the high

voltage section. This function is normally accom-

plished by a high voltage fast recovery diode (fig.

4a). In the L6385 a patented integrated structure

replaces the external diode. It is realized by a

high voltage DMOS, driven synchronously with

the low side driver (LVG), with in series a diode,

as shown in fig. 4b

An internal charge pump (fig. 4b) provides the

DMOS driving voltage .

The diode connected in series to the DMOS has

been added to avoid undesirable turn on of it.

CBOOT selection and charging:

To choose the proper CBOOT value the external

MOS can be seen as an equivalent capacitor.

Figure 3. Quiescent Current vs. Supply

Voltage

Iq

(µA)

104

D99IN1055

103

102

10

0 2 4 6 8 10 12 14 16 VS(V)

This capacitor CEXT is related to the MOS total

gate charge :

CEXT

=

Qgate

Vgate

The ratio between the capacitors CEXT and CBOOT

is proportional to the cyclical voltage loss .

It has to be:

CBOOT>>>CEXT

e.g.: if Qgate is 30nC and Vgate is 10V, CEXT is

3nF. With CBOOT = 100nF the drop would be

300mV.

If HVG has to be supplied for a long time, the

CBOOT selection has to take into account also the

4/9

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