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Transcript
Design Note, V1.0, Mar. 2003
T D A4 8 6 3
DN-PFC-TDA4863-1
TDA4863 Driving MOSFET with large
Capacitances
BDTIC
Author: Wolfgang Frank
http://www.infineon.com/pfc
Power Management & Supply
www.BDTIC.com/infineon
N e v e r
s t o p
t h i n k i n g .
TDA4863 Driving MOSFET with large Capacitances
Revision History:
2003-03
V1.0
Previous Version:
Page
Subjects (major changes since last revision)
For questions on technology, delivery and prices please contact the Infineon
Technologies Offices in Germany or the Infineon Technologies Companies and
Representatives worldwide: see our webpage at http://www.infineon.com.
CoolMOSTM, CoolSETTM are a trademarks of Infineon Technologies AG.
BDTIC
Edition 2003-03
Published by Infineon Technologies AG,
St.-Martin-Strasse 53,
81669 München, Germany
© Infineon Technologies AG 2003.
All Rights Reserved.
Attention please!
The information herein is given to describe certain components and shall not be considered as warranted
characteristics.
Terms of delivery and rights to technical change reserved.
We hereby disclaim any and all warranties, including but not limited to warranties of non-infringement, regarding
circuits, descriptions and charts stated herein.
Infineon Technologies is an approved CECC manufacturer.
Information
For further information on technology, delivery terms and conditions and prices please contact your nearest
Infineon Technologies Office in Germany or our Infineon Technologies Representatives worldwide.
Warnings
Due to technical requirements components may contain dangerous substances. For information on the types in
question please contact your nearest Infineon Technologies Office.
Infineon Technologies Components may only be used in life-support devices or systems with the express written
approval of Infineon Technologies, if a failure of such components can reasonably be expected to cause the failure
of that life-support device or system, or to affect the safety or effectiveness of that device or system. Life-support
devices or systems are intended to be implanted in the human body, or to support and/or maintain and sustain
and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may
be endangered.
www.BDTIC.com/infineon
TDA4863 Driving MOSFET with large
Capacitances
1
DN-PFC-TDA4863-1
Large Capacitances
In adapters MOSFET with a lower on-state resistances RDS(on) are often used in order to
reduce power losses. But such transistors have typically large capacitances Ciss, Coss,
and Crss according to Figure 1. Especially in power factor correction (PFC)
preconverters this issue is even more dramatically, because there are points of
operation, at which the drain-source-voltage is very low or even zero. At those points,
the parasitic drain-gate-capacitance Crss(VDS) (“Miller-capacitance”) increases highly
nonlinearly. This can be easily seen in the datasheets of the MOSFET, as it is shown in
figure 24 of [2].
BDTIC
Lboost
ton
toff
tosc
TP
VCC
idisplace
iL
D
Crss
vDS
RG
idisplace
Gate
Coss
G
Q1
Ciss
S
vGate
RG
Figure 1
Equivalent Circuit of a MOSFET with parasitic Capacitors
In discontinuous conduction mode (DCM) the drain-source-voltage swings down to zero
by system, if the input voltage is lower than 50% of the output voltage even without the
MOSFET being switched on. This means that the drain potential also goes down to zero
which will cause a capacitive current flowing into the gate pin of the MOSFET and
through the capacitor Crss.
The larger the capacitance Crss the larger is the amplitude of the capacitive current. This
may reverse bias the lower gate drive transistor and may lead to substrate currents in
the control IC of the MOSFET and may cause malfunction. Substrate current can be
Design Note
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6
V1.0, 2003-03
TDA4863 Driving MOSFET with large Capacitances
Large Capacitances
detected easily by measuring the voltage at the gate drive pin. Substrate currents cause
a voltage of about -0,7 V.
This effect is well known. Usually schottky diodes are used directly at the gate drive pin
to ground according to Figure 2 in order to clamp the gate drive voltage of -0,3 V
minimum.
MUR460
D5
VOUT
R9
33k
R4A
Q1
SPP20N60 422k
C3
R10
R4
422k
12Ω
Schottky
BDTIC
TDA4863
5
6
Figure 2
7
1
2
4
C8
C2
1µ
R2
33k
C1
2,2µ
R11
0R47||
0R47
100µF
450V
R5
5k1
C1
µ1
GND
Gate Drive Design of TDA4863 with Schottky Clamp Diode
The rating of the schottky diode depends on the peak value and the rms value of the
clamp current. But typically small signal schottky diodes with a forward current capability
of approximately 100 mA are already sufficient.
Design Note
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7
V1.0, 2003-03
TDA4863 Driving MOSFET with large Capacitances
Summary of Used Nomenclature
2
Summary of Used Nomenclature
Physics:
General identifiers:
Special identifiers:
A .........cross area
b, B .....magnetic inductance
c, C .....capacitance
d, D .....duty cycle
f...........frequency
i, I ........current
l, L .......inductance
N .........number of turns
p, P .....power
t, T.......time, time-intervals
v, V......voltage
W ........energy
h..........efficiency
AL ........... inductance factor
V(BR)CES .. collector-emitter breakdown
voltage of IGBT
VF........... forward voltage of diodes
Vrrm .......... maximum reverse voltage of diodes
BDTIC
big letters:
constant values and time
intervals
small letters: time variant values
K1, K2 ..ferrite core constants
Components:
C .........capacitor
D .........diode
IC ........integrated circuit
L..........inductor
R .........resistor
TR .......transformer
Indices:
AC.......alternating current value
DC.......direct current value
BE .......basis-emitter value
CS.......current sense value
OPTO..optocoupler value
P .........primary side value
Pk........peak value
R........... reflected from secondary to primary side
S .........secondary side value
Sh .......shunt value
UVLO ..undervoltage lockout value
Z..........zener value
Design Note
fmin ......... value at minimum pulse frequency
i ..............running variable
in ............input value
max ........maximum value
min .........minimum value
off ...........turn-off value
on ...........turn-on value
out ..........output value
p .............pulsed
rip ...........ripple value
1, 2, 3 .....on-going designator
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8
V1.0, 2003-03
TDA4863 Driving MOSFET with large Capacitances
References
3
References
[1]
Infineon Technologies AG: TDA4863 - Power factor controller; Preliminary
Data sheet; Infineon Technologies AG ; Munich; Germany; 02 / 02.
[2]
Infineon Technologies AG: SPP20N60C3 CoolMOS - Power Transistor; Data
sheet; Infineon Technologies AG ; Munich; Germany; 10 / 02.
BDTIC
Design Note
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9
V1.0, 2003-03
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BDTIC
Dr. Ulrich Schumacher
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www.BDTIC.com/infineon
Published by Infineon Technologies AG