TDA4605
CONTROL CIRCUIT FOR SWITCH MODE POWER SUPPLIES
USING MOS TRANSISTORS
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.
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FOLD-BACK CHARACTERISTIC PROVIDES
OVERLOAD PROTECTION FOR EXTERNAL
DIODES
BURST OPERATION UNDER SHORT-CIR-
CUIT AND NO LOAD CONDITIONS
LOOP ERROR PROTECTION
SWITCH-OFF IN CASE OF TOO LOW LINE
VOLTAGE (under voltage switch-off)
LINE VOLTAGE COMPENSATION OF OVER-
LOAD POINT
SOFT-START FOR SMOOTH START-UP
CHIP OVER-TEMPERATURE PROTECTION
(thermal shutdown)
ON-CHIP PARASITIC TRANSFORMER OS-
CILLATION SUPPRESSION CIRCUITRY
DECREASE OF REGULATED VOLTAGE FOR
LOW POWER CONSUMPTION
DIP8
(Plastic Package)
ORDER CODE :
TDA4605
DESCRIPTION
The IC TDA4605 controls the MOS Power Transis-
tor and performs all necessary regulation and
monitoring functions in free running flyback con-
verters. Since good load regulation over a wide
load range is attained, this IC is particularly suitable
for Consumer as well as Industrial Power Supplies.
Alternative source of the TDA4605 is also avail-
able from SIEMENS Semiconductors Consumer
Electronics A.G.
PIN CONNECTIONS
SO8
(Plastic Micropackage)
ORDER CODE :
TDA4605D
REGULATION INPUT
PRIMARY CURRENT SIMULATION
PRIMARY VOLTAGE MONITORING
GROUND
1
2
3
4
8
7
6
5
ZERO CROSSING DETECTOR INPUT
SOFT-START
SUPPLY VOLTAGE
OUTPUT
4605-01.EPS
April 1996
1/6
TDA4605
PIN CONFIGURATION
Pin
Number
1
Description
Regulating voltage : information input concerning secondary voltage.
By comparing the regulating voltage obtained from the regulating winding of the transformer with the
internal reference voltage, the output pulse width on Pin 5 is adapted to the load of the secondary side
(normal, overload, short circuit, no load)
Primary current simulation : 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 value is
reached that is derived from the regulating voltage at Pin 1, the output pulse at Pin 5 is terminated. The
RC element serves to set the maximum power at the overload point.
Primary voltage detector : input for primary voltage monitoring. When the line voltage is too low the IC is
switched-off by comparing V
3
with an internal reference. Voltage at Pin 3 is used for overload point
compensation.
Ground
Output : push-pull output for charge and discharge of the gate capacitance of the power MOS transistor.
Supply voltage : Supply voltage input. From it are derived a stable internal reference voltage (V
REF
) and
the switching threshold V
6A
, V
6E
, V
6 max
and V
6 min
for the supply voltage detector.
if V
6
> V
6E
the V
REF
is switched on and switched off when V
6
< V
6A
. In addition the logic is only enable for
V
6 min
< V
6
< V
6 max
.
Soft-start : input for soft-start and integration network. Start-up will begin with short pulses by connecting a
capacitor between Pin 7 to ground. This capacitor together with a resistor connected between Pin 7 and
error amplifier output also as acts an integrator network for regulation.
Zero detector : Input for the oscillator feedback. After starting oscillator, every zero transit of the feedback
voltage (falling edge) triggers an output pulse at Pin 5. The trigger threshold is at typically - 50mV
2
3
4
5
6
7
8
BLOCK DIAGRAM
6
2
5
TDA4605
Re fere nce
Voltage
(typ. 3V)
S upply
Voltage
Monitor
V
2B
P rima ry
Current
Recopy
Output S ta ge
a nd
Current Limit
V
REF
4
V
6min
V
6A
V
6E
V
6ma x
V
s t
S ta rting
Impulse
Genera tor
Logic
Current
S ource
1
V
R
Regulating
& Ove rload
Amplifier
S top
Comp.
Zero
Cros s ing
De te ctor
4605-02.EPS
Ove rloa d
Point
Corre ction
V
u
Low Volta ge
P rote ction
Monitoring
7
3
8
2/6
4605-01.TBL
TDA4605
ABSOLUTE MAXIMUM RATINGS
Symbol
V
1
V
2
V
3
V
4
V
6
V
7
I
1
I
2
I
3
I
4
I
5
I
6
I
7
I
8
T
j
T
stg
Parameter
Pin
1
2
3
4
6
7
1
2
3
4
5
6
7
8
Value
-0.3, +3
-0.3
-0.3
-0.3
-0.3, +20
-0.3
3
3
3
- 1.5
-0.5, +1.5
0.5
3
-3, +3
+125
-40, +125
Unit
V
V
V
V
V
V
mA
mA
mA
A
A
A
mA
mA
o
C
o
C
Supply Voltage
Supply Current
t
p
≤
50µs, V
≤
0.1
t
p
≤
50µs, V
≤
0.1
t
p
≤
50µs, V
≤
0.1
Junction Temperature (autom. thermal disjunction)
Storage Temperature
THERMAL DATA
Symbol
R
th(j-a)
R
th(j-c)
T
amb
Parameter
Junction-ambient Thermal Resistance
Junction-case Thermal Resistance
Ambient Temperature
Value
80
45
-20, +85
Unit
C/W
o
C/W
o
C
o
ELECTRICAL CHARACTERISTICS
(V
CC
= 10V, T
amb
= 25
o
C, unless otherwise specified)
Symbol
START-UP HYSTERESIS
I
6E0
V
6E
V
6A
I
6E1
I
6A1
V
2(Max.)
V
3(Max.)
V
1R
-V
R
Start-up Current Drain
Switch-on Voltage
Switch-off Voltage
Switch-on Current
Switch-off Current
At Pin 2 (V
6
< V
6E
)
At Pin 3 (V
6
< V
6E
)
Control Input Voltage
Voltage Gain of the Control Circuit in the Control
Range
Basic Value
Peak Value in the Range of Secondary Overload
Maximum Ramp Amplitude
Peak Value in the Range of Secondary Short
Circuit Operation
Foldback Point Correction Current
V
1
= V
1R
- 10mV
V
2O
- V
2B
V
1
= 0
V
6
= V
6E
11
4.5
V
6
= V
6E
V
6
= V
6A
I
2
= 1mA
I
3
= 1mA
5.6
5.6
400
V
R
= d(V
2S
- V
2B
)/dV
1
f = 1kHz
0.955
2.8
1.82
2.3
0.6
12
5
11
10
6.6
6.6
410
43
0.8
13
5.5
mA
V
V
mA
mA
V
V
mV
dB
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
VOLTAGE CLAMP (V
6
= 10V, IC Switched off)
9
9
420
CONTROL RANGE
PRIMARY CURRENT SIMULATION VOLTAGE
V
2B
V
2O
DV
2
V
2S
1.00
2.95
1.95
2.5
1.03
3.1
2.08
2.7
V
V
V
V
4605-04.TBL
OVERLOAD RANGE AND SHORT CIRCUIT OPERATION
FOLDBACK POINT CORRECTION
-I
2
V
3
= 3.7V
300
500
650
µA
3/6
4605-03.TBL
4605-02.TBL
TDA4605
ELECTRICAL CHARACTERISTICS
(V
CC
= 10V, T
amb
= 25
o
C, unless otherwise specified) (continued)
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
GENERALLY VALID DATA (V
6
= 10V)
VOLTAGE OF THE ZERO Transition DETECTOR
V
8P
V
8N
V
8S
TUL
-I
8
Positive Clamping Voltage
Negative Clamping Voltage
Threshold Value
Suppression of Transformer Ringing
Input Current
I
8
= 1mA
I
8
= -1mA
40
3
0
0.75
-0.2
50
3.8
V
V
mV
µs
µV
V
8
= 0
4.5
4
PUSH-PULL OUTPUT STAGE
SATURATION VOLTAGES
V
SatU
V
SatU
V
SatU
+dV
5
/dt
-dV
5
/dt
-I
1
V
6(Min.)
V
6(Max.)
V
3A
Oj
V
3Sat
I
6
Pin 5 Sourcing
Pin 5 Sinking
Pin 5 Sinking
Rising Edge
Falling Edge
Current to reduce the Control Voltage
Undervoltage Protection for V
6
:
Voltage at Pin 5 = V
5(Min.)
if V
6
< V
6(Min.)
Overvoltage Protection for V
6
:
Voltage at Pin 5 = V
5(Min.)
if V
6
> V
6(Max.)
Undervoltage Protection for V
AC
:
Voltage at Pin 5 = V
5(Min.)
if V
3
< V
3A
Over Temperature : at the given chip temperature the
IC will switch V
5
to V
5(Min.)
Voltage at Pin 3 if one of the protection functions was
triggered ; (V
3
will be clamped until V
6
< V
6A
)
Current Drain during Burst Operation
V
7
= 1V
7.0
15
V
2
= 0V
970
I
5
= -0.1A
I
5
= +0.1A
I
5
= +0.5A
1.5
1.0
1.4
70
100
50
7.25
16
1005
150
I
3
= 750µA
V
3
= V
2
= 0V
0.4
8
0.8
7.5
16.5
1040
2.0
1.2
1.8
V
V
V
V/µs
V/µs
µA
V
V
mV
o
OUTPUT SLOW RATE
REDUCTION OF CONTROL VOLTAGE
PROTECTION CIRCUIT
C
4605-05.TBL
V
mA
FUNCTIONAL DESCRIPTION
In free running fly-back converters, the TDA4605
assumes control of a MOS power transistor and all
necessary regulation and monitoring functions.
The serial circuit of power transistor and primary
winding of the flyback transformer is connected to
the input voltage. During the switch-on period of the
transistor, energy is stored in the transformer and
during the switch-off period it is fed to te load via
the secondary winding. By varing the 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 inde-
pendent 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 begins as soon as the energy stored in
the transformer has been totally delivered to the
4/6
secondary side.
In different load ranges, the SMPS will behave as
follows :
-
No-Load Operation :
The power supply unit
oscillates in non continuous mode at a typical
frequency of 20 to 40kHz. Depending upon the
transformer winding and the regulated voltage
divider, the output voltage can be slightly above
the nominal value.
-
Normal Operation :
Starting from typ. 200kHz,
the switching frequency falls with increasing load
and decreasing AC voltage. The duty cycle de-
pends primarily on the AC voltage. The output
voltage is only slightly load-dependen t.
-
OverloadPoint :
Maximum output power is avail-
able at this point of the output characteristics
-
Overload :
The energy transferred per operation
cycle is limited at the top. Therefore, the output
voltage will fall with secondary oveloading.
TDA4605
PACKAGE MECHANICAL DATA
8 PINS - PLASTIC DIP
Dimensions
A
a1
B
b
b1
D
E
e
e3
e4
F
I
L
Z
Min.
0.51
1.15
0.356
0.204
7.95
Millimeters
Typ.
3.32
Max.
Min.
0.020
0.045
0.014
0.008
0.313
Inches
Typ.
0.131
Max.
1.65
0.55
0.304
10.92
9.75
2.54
7.62
7.62
6.6
5.08
3.81
1.52
0.065
0.022
0.012
0.430
0.384
0.100
0.300
0.300
0260
0.200
0.150
0.060
3.18
0.125
5/6
DIP8.TBL
PM-DIP8.EPS
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