Datasheet, V2.0, 1 Jul 2002
PWM-QR IC
TDA4605-3
Control IC for Switched-Mode
Power Supplies using
MOS-Transistors
Power Management & Supply
N e v e r
s t o p
t h i n k i n g .
TDA4605-3
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Subjects (major changes since last revision)
2002-07-01
Datasheet
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Edition 2002-07-01
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Infineon Technologies AG 1999.
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be endangered.
Control IC for Switched-Mode Power Supplies
using MOS-Transistor
TDA 4605-3
Bipolar IC
Features
q
Fold-back characteristics provides overload protection for
q
q
q
q
q
q
q
q
external components
Burst operation under secondary short-circuit condition
implemented
Protection against open or a short of the control loop
Switch-off if line voltage is too low (undervoltage switch-off)
Line voltage depending compensation of fold-back point
Soft-start for quiet start-up without noise generated by the
transformer
Chip-over temperature protection implemented (thermal
shutdown)
On-chip ringing suppression circuit against parasitic
oscillations of the transformer
AGC-voltage reduction at low load
P-DIP-8-1
Type
TDA 4605-3
Ordering Code
Q67000-A5066
Package
P-DIP-8-1
The IC TDA 4605-3 controls the MOS-power transistor and performs all necessary control and
protection functions in free running flyback converters. Because of the fact that a wide load range
is achieved, this IC is applicable for consumer as well as industrial power supplies.
The serial circuit and primary winding of the flyback transformer are connected in series to the input
voltage. During the switch-on period of the transistor, energy is stored in the transformer. During the
switch-off period the energy is fed to the load via the secondary winding. By varying switch-on time
of the power transistor, the IC controls each portion of energy transferred to the secondary side
such that the output voltage remains nearly independent of load variations. The required control
information is taken from the input voltage during the switch-on period and from a regulation winding
during the switch-off period. A new cycle will start if the transformer has transferred the stored
energy completely into the load.
Version 2.0
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TDA 4605-3
In the different load ranges the switched-mode power supply (SMPS) behaves as follows:
No load operation
The power supply is operating in the burst mode at typical 20 to 40 kHz. The output voltage can be
a little bit higher or lower than the nominal value depending of the design of the transformer and the
resistors of the control voltage divider.
Nominal operation
The switching frequency is reduced with increasing load and decreasing AC-voltage.
The output voltage is only dependent on the load.
Overload point
Maximal output power is available at this point of the output characteristic.
Overload
The energy transferred per operation cycle is limited at the top. Therefore the output voltages
declines by secondary overloading.
Version 2.0
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1 Jul 2002
TDA 4605-3
Pin Definitions and Functions
Pin No.
1
Function
Information Input Concerning Secondary Voltage.
By comparing the
regulating voltage - obtained trom the regulating winding of the transformer - with
the internal reference voltage, the output impulse width on pin 5 is adjusted to the
load of the secondary side (normal, overload, short-circuit, no load).
Information Input Regarding the Primary Current.
The primary current rise in
the primary winding is simulated at pin 2 as a voltage rise by means of external
RC-element. When a voltage level is reached thats derived from the regulating
voltage at pin 1, the output impulse at pin 5 is terminated. The RC-element serves
to set the maximum power at the overload point set.
Input for Primary Voltage Monitoring:
In the normal operation
V
3
is moving
between the thresholds
V
3H
and
V
3L
(V
3H
>
V
3
>
V
3L
).
V
3
<
V
3L
: SMPS is switched OFF (line voltage too low).
V
3
>
V
3H
: Compensation of the overload point regulation (controlled by pin 2)
starts at
V
3H
:
V
3L
= 1.7.
Ground
Output:
Push-pull output provides
±
1 A for rapid charge and discharge of the
gate capacitance of the power MOS-transistor.
Supply Voltage Input:
A stable internal reference voltage
V
REF
is derived from
the supply voltage also the switching thresholds
V
6A
,
V
6E
,
V
6 max
and
V
6 min
for
the supply voltage detector. If
V
6
>
V
6E
then
V
REF
is switched on and swiched off
when
V
6
<
V
6A
. In addition the logic is only enable for
V
6 min
<
V
6
<
V
6 max
.
Input for Soft-Start.
Start-up will begin with short pulses by connecting a
capacitor from pin 7 to ground.
Input for the Oscillation Feedback.
After starting oscillation, every zero
transition of the feedback voltage (falling edge) through zero (falling edge)
triggers an output pulse at pin 5. The trigger threshold is at + 50 mV typical.
2
3
4
5
6
7
8
Version 2.0
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1 Jul 2002
Embedded System
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