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L6387 View Datasheet(PDF) - STMicroelectronics

Part Name
Description
MFG CO.
L6387
ST-Microelectronics
STMicroelectronics ST-Microelectronics
'L6387' PDF : 9 Pages View PDF
1 2 3 4 5 6 7 8 9
L6387
Figure 1. 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
Input Logic
L6387 Input Logic is VCC (17V) compatible. An in-
terlocking features is offered (see truth table be-
low) to avoid undesired simultaneous turn ON of
both Power Switches driven.
Table 1.
Input
Output
HIN
LIN
HVG
LVG
0
0
1
1
0
1
0
1
0
0
1
0
0
1
0
0
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.
3a). In the L6387 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. 3b
An internal charge pump (fig. 3b) 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.
This capacitor CEXT is related to the MOS total
gate charge :
Figure 2. Quiescent Current vs. Supply
Voltage
Iq
(µA)
104
D99IN1055
103
102
10
0 2 4 6 8 10 12 14 16 VS(V)
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
leakage losses.
e.g.: HVG steady state consumption is lower than
200µA, so if HVG TON is 5ms, CBOOT has to
supply 1µC to CEXT. This charge on a 1µF ca-
pacitor means a voltage drop of 1V.
The internal bootstrap driver gives great advan-
tages: the external fast recovery diode can be
avoided (it usually has great leakage current).
This structure can work only if VOUT is close to
GND (or lower) and in the meanwhile the LVG is
on. The charging time (Tcharge ) of the CBOOT is
the time in which both conditions are fulfilled and
it has to be long enough to charge the capacitor.
The bootstrap driver introduces a voltage drop
due to the DMOS RDSON (typical value: 125
Ohm). At low frequency this drop can be ne-
glected. Anyway increasing the frequency it
must be taken in to account.
The following equation is useful to compute the
4/9
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