M51995 Mitsubishi, M51995 Datasheet - Page 24

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M51995

Manufacturer Part Number
M51995
Description
SWITCHING REGULATOR CONTROL
Manufacturer
Mitsubishi
Datasheet

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Output circuit
(1)The output terminal characteristics at the Vcc voltage
Fig.41 shows the relation between the applied gate voltage
and the stored gate charge.
In the region 1 ,the charge is mainly stored at C
depletion is spread and C
MOS-FIT and the high drain voltage.
In the region 2 ,the C
the characteristics of MOS-FIT transfers from off-state to on-
state.
In the region 3 ,both the C
characteristics as the MOS-FIT is on-state and the drain
voltage is low.
(2)MOS-FIT gate drive power dissipation
The output terminal has the current sink ability even though the
Vcc voltage lower than the "Operation-stop" voltage or Vcc(
(It means that the terminal is "Output low state" and please refer
characteristics of output low voltage versus sink current.)
This characteristics has the merit not to damage the MOS-FIT
at the stop of operation when the Vcc voltage decreases lower
than the voltage of Vcc(
FIT,which shows the capacitive load characteristics to the
output terminal,is drawn out rapidly.
The output terminal has the draw-out ability above the Vcc
voltage of 2V,however,lower than the 2V,it loses the ability and
the output terminal potential may rise due to the leakage
current.
In this case, it is recommended to connect the resistor of 100k
between gate and source of MOS-FIT as shown in Fig.40.
Fig.39 Application circuit diagram to keep the
Fig.40 Circuit diagram to prevent the MOS-FIT gate
lower than the "Operation-stop" voltage
non-operating condition when over load
current condition will continue for specified
duration
potential rising
M51995A
M51995A
GD
STOP
is multiplied by the "mirror effect" as
GD
OVP
V
CT
OUT
GD
),as the gate charge of MOS-
is small owing to the off-state of
and C
C
T
GS
affect to the
100k
TO MAIN
TRANSFORMER
Vcc
GS
R
as the
CLM
STOP
(
)
24
15
10
20
0
5
/ 27 )
0
Fig.41 The relation between applied gate-source
1
The charging and discharging current caused by this gate
charge makes the gate power dissipation.The relation between
gate drive current I
following equation;
As the gate drive current may reach up to several tenths
milliamperes at 500kHz operation,depending on the size of
MOS-FIT,the power dissipation caused by the gate current can
not be neglected.
It is recommended to use the output buffer circuit as shown in
Fig.42,when type M51995A drives the large capacitive load or
bipolar transistor.
Where
(3)Output buffer circuit
In this case,following action will be considered to avoid heat
up of type M51995A.
(1) To attach the heat sink to type M51995A
(2) To use the printed circuit board with the good thermal
(3) To use the buffer circuit shown next section
TOTAL STORED GATE CHARGE(nC)
f
I
OSC
D
conductivity
voltage and stored gate charge
=Q
4
is switching frequency
GSH
2
V
V
V
• f
SWITCHING REGULATOR CONTROL
DS
DS
DS
OSC
MITSUBISHI (Dig./Ana. INTERFACE)
=80V
=200V
=320V
8
D
.....................................(11)
and total gate charge Q
3
12
I
D
M51995AP/FP
=4A
16
GSH
20
GATE
is shown by
C
V
GD
GS
C
GS
SOURCE
DRAIN
C
I
D
DS
V
D

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