TDA8380A Datasheet, PDF (5/20 Pages) NXP Semiconductors – Control circuit for switched mode power supplies

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 (V_CCmin) can be set externally with a resistor connected between
the V_CCmin pin (pin 4) and ground (pin 14) (see Fig.3).
Fig.3 Trip level setting of minimum V_CC protection level.
V_CCmin 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 V_CCmin pin is connected to V_CC, the start-up circuit is then inhibited and the device
starts operating when V_CC 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
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