TDA4605 Datasheet, PDF (4/6 Pages) STMicroelectronics – CONTROL CIRCUIT FOR SWITCH MODE POWER SUPPLIES USING MOS TRANSISTORS

TDA4605
ELECTRICAL CHARACTERISTICS (VCC = 10V, Tamb = 25^oC, unless otherwise specified) (continued)
Symbol
Parameter
Test Conditions Min. Typ. Max. Unit
GENERALLY VALID DATA (V6 = 10V)
VOLTAGE OF THE ZERO Transition DETECTOR
V_8P Positive Clamping Voltage
V8N Negative Clamping Voltage
V_8S Threshold Value
TUL Suppression of Transformer Ringing
-I8
Input Current
PUSH-PULL OUTPUT STAGE
SATURATION VOLTAGES
I₈ = 1mA
I8 = -1mA
V8 = 0
0.75
V
-0.2
V
40
50
mV
3
3.8 4.5 µs
0
4
µV
VSatU Pin 5 Sourcing
V_SatU Pin 5 Sinking
VSatU Pin 5 Sinking
OUTPUT SLOW RATE
I5 = -0.1A
I₅ = +0.1A
I5 = +0.5A
1.5 2.0 V
1.0 1.2 V
1.4 1.8 V
+dV5/dt Rising Edge
-dV₅/dt Falling Edge
REDUCTION OF CONTROL VOLTAGE
70
V/µs
100
V/µs
-I₁
Current to reduce the Control Voltage
PROTECTION CIRCUIT
V₇ = 1V
50
µA
V6(Min.)
V6 (Max.)
V3A
Oj
V3Sat
I₆
Undervoltage Protection for V6 :
Voltage at Pin 5 = V5(Min.) if V6 < V6(Min.)
Overvoltage Protection for V6 :
Voltage at Pin 5 = V_5(Min.) if V₆ > V_6(Max.)
Undervoltage Protection for VAC :
Voltage at Pin 5 = V_5(Min.) if V₃ < V_3A
Over Temperature : at the given chip temperature the
IC will switch V5 to V5(Min.)
Voltage at Pin 3 if one of the protection functions was
triggered ; (V3 will be clamped until V6 < V6A)
Current Drain during Burst Operation
V2 = 0V
I3 = 750µA
V₃ = V₂ = 0V
7.0 7.25 7.5 V
15
16 16.5 V
970 1005 1040 mV
150
o_C
0.4 0.8 V
8
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
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.
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