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PDF TDA8380 Data sheet ( Hoja de datos )
| Número de pieza | TDA8380 | |
| Descripción | Control circuit for switched mode power supplies | |
| Fabricantes | NXP Semiconductors | |
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INTEGRATED CIRCUITS
DATA SHEET
TDA8380A
Control circuit for switched mode
power supplies
Product specification
Supersedes data of October 1993
File under Integrated Circuits, IC02
November 1993
1 page  
Philips Semiconductors
Control circuit for switched mode power supplies
Product specification
TDA8380A
FUNCTIONAL DESCRIPTION
The TDA8380A is a control circuit which generates the pulses required to drive the switching transistor in a switched
mode power supply (SMPS).
Supply
This device is intended to be used on the primary side of the power supply and can be supplied via a take-over (auxiliary)
winding on the transformer.
The device is initialized via a high value resistor connected between the rectified mains voltage and the device’s supply
pin (pin 5), which causes the capacitor connected to this pin to charge slowly. When the voltage exceeds the initialization
level (typically 17 V) the device will start up and the duty cycle will be slowly increased by the slow-start circuit. After a
short period the take-over winding will supply the device. The value of the resistor is normally defined by the time taken
to charge the capacitor.
A one second delay between switching on and operation of the power supply is acceptable in most cases.
The operating voltage range is from 9 to 20 V. The supply pin is protected by a 23 V Zener diode. The supply protection
circuit is activated once the Zener diode is conducting. The slow-start procedure begins after initialization, until then the
output is off. The current drawn by the device during the initialization period is less than 150 µA.
When the supply voltage falls below the minimum trip level, the device switches off and the start-up procedure is
repeated. The minimum voltage supply threshold setting (VCCmin) can be set externally with a resistor connected between
the VCCmin pin (pin 4) and ground (pin 14) (see Fig.3).
Fig.3 Trip level setting of minimum VCC protection level.
VCCmin can be set between 8.4 V (an internally fixed overriding protection level) and 17 V by means of an external resistor
connected to pin 4.
When choosing the initialization and minimum supply voltages the following should be taken into account:
• The difference between the two voltages should be large enough to enable a supply voltage dip during start-up.
• The value of the minimum supply voltage should be high enough to ensure that the high-voltage transistor is correctly
driven. A high protection level makes it possible to have a large resistor value in series with the base drive.
For battery line input operation, the VCCmin pin is connected to VCC, the start-up circuit is then inhibited and the device
starts operating when VCC exceeds the 8.4 V protection level (this level has a hysteresis of approximately 50 mV). The
device draws current continuously under these conditions.
November 1993
5
5 Page 
Philips Semiconductors
Control circuit for switched mode power supplies
Product specification
TDA8380A
Fig.10 Current protection.
Slow-start circuit
A slow-start occurs:
• At Switch-on of the SMPS
• After a current trip as described in the section Over-current protection
• After a low or high VCC trip.
The capacitor at the SS input is discharged and the slow-start bistable is reset when the voltage at the SS input falls
below 0.5 V after which the circuit is ready for a slow-start. The dead time (during which the capacitor at the SS input is
being charged to the 1.4 V lower level of the sawtooth) before duty cycle regulation starts is minimal. The SS input can
also be used for Dmax setting by connecting a resistor to ground. The voltage across this resistor is then limited to
1/6 × Vref × R12/R6.
Output stages
The output stage consists of two NPN darlington transistors, their collector and emitter connected to separate pins (see
Fig.13). The top transistor is capable of sourcing a maximum of 0.75 A to the high-voltage transistor while the bottom
transistor can sink peak currents up to 2.5 A.
For low currents up to 10 mA, the saturation voltage of the sink darlington transistor is similar to that of a single transistor
(see Fig.11). During switching of this transistor dV/dt is internally limited to reduce interference.
Care should be taken with the external wiring of the output pins to avoid oscillation or interference due to parasitic
inductance and wire resistance.
During start-up a small current flows from VCC to E2 to precharge the series capacitor at the output (see Fig.13).
November 1993
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet TDA8380.PDF ] | |
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