MC33198 データシートの表示（PDF） - Motorola => Freescale
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MC33198 Datasheet PDF : 11 Pages
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MC33198
This resistor will reduce in some way the charge pump
output voltage available for the MOSFET, but the device will
still provide enough Gate-to-Source voltage to maintain the
MOSFET on in good conditions. The resistor will mainly act as
an additional discharge current, which will reduce the
switching off time of the overall application. See the table 2
below and figure 11 which show the pin 4 voltage depending
on the additional gate resistor and the off switching time due
to this resistor.
If a very low switching time is needed, the resistor has to
be extremely low, resulting in low gate voltage not high
enough to ensure proper MOSFET operation. In this case, a
logic level MOSFET can be used. Logic level will operate with
Vgs of 5V with the same performance as a standard MOSFET
having a 12V Vgs. Care should be taken regarding maximum
gate to source voltage of a logic level MOSFET. An additional
zener might be necessary to prevent gate oxyde damages.
Table 2 •Switching Off Characteristics with
MOSFET Additional Gate Resistor
Rgate
VCC (V)
Vgate (V)
Toff
No R
7
16
450
10
23
700
14
28
750
20
34
780
68 kΩ
7
14
160
10
22
230
14
27
230
20
33
220
39 kΩ
7
13
100
10
21
160
14
26
160
20
32
150
15 kΩ
7
11
30
10
17,5
50
14
24
50
20
28,5
50
NOTE 1 : Time from negative edge of input signal (Pin 7) to negative edge
of gate voltage (Pin 4) measured at 5V threshold.
NOTE 2 : Gate discharge time, not LOAD switching OFF time.
NOTE 3 : TMOS used is Motorola MTP50N06, load 10Ω resistor.
Reverse Battery
The device does not sustain reverse battery operation for
Vcc voltage greater than - 0,6V in magnitude. In application,
pin 5 should be protected from reverse battery by connecting
a diode in series with the Vbat line.
Figure15.
Vbat
Vbat
5
VCC
6 STATUS
DRN 2
GATE 4
7 INPUT
GND
3
SOURCE 1
TIMER
8
C
R drn
1K
LOAD
Pin 2 which is normally connected to resistor, can sustain
reverse battery operation, providing that the DRN resistor is
higher than 3,3K. A 1K resistor at pin 1 is also necessary to
limit the reverse current flowing through the MOSFET body
diode.
Figure16. MC33198 Gnd Disconnection Circuitry
5V
Vbat
Vbat
Device drive
circuitry and
interface
6
IN
7
Module Gnd
5
MC33198
8
3
C
4
1
R1
LOAD
Q1
Additional circuitry
to present MOSFET
turn-on in case of module
Gnd disconnection
R1 = 3,3K
Q1 = 2N2222
Operation
When module Gnd is disconnected and if VBAT
connection is still present, pin 3 of MC33198 goes to about 2/3
of Vbat if additional circuitry is not inserted.
With R1/Q1, Gate/Source voltage of MOSFET is shorted
as soon as pin 3 voltage rises above Gnd level.
MC33198
MOTOROLA
9
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