TDA4863-2

Functional Description

Version 2.1

11

22 Feb 2005

To prevent false tripping the zero current detector is designed as a Schmitt-Trigger with

a hysteresis of 0.5 V. An internal 5 V clamp protects the input from overvoltage

breakdown, a 0.6 V clamp prevents substrate injection. An external resistor has to be

used in series with the auxiliary winding to limit the current through the clamps.

2.8

Restart Timer

The restart timer function eliminates the need of an oscillator. The timer starts or restarts

the TDA4863-2 when the driver output has been off for more than 150 µs after the

inductor current reaches zero.

2.9

Undervoltage Lockout

An undervoltage lockout circuitry switches the IC on when V

threshold V

During start up the supply current is less then 100 µA.

An internal voltage clamp has been added to protect the IC from V

condition. When using this clamp special care must be taken on power dissipation.

Start up current is provided by an external start up resistor which is connected from the

AC line to the input supply voltage V

the application board. Otherwise the IC can be destroyed due to the high capacitor

voltage.

Bootstrap power supply is created with the previous mentioned auxiliary winding and a

diode (see “Application Circuit” on Page 21).

2.10

Gate Drive

The TDA4863-2 totem pole output stage is MOSFET compatible. An internal protection

ciruitry is activated when V

is turned off. The totem pole output has been optimized to achieve minimized cross

conduction current during high speed operation.

Compared to TDA4863 a bigger MOS Transistor can be driven by the TDA4863-2. When

a big MOSFET is used in applications with TDA4863, for example SPP20N60C3, the

falling edge of the gate drive voltage can swing under GND and can cause false

triggering of the IC. To prevent false traiggering the gate drive voltage of theTDA4863-2

at low state and gate current I

The difference between TDA4863-2 and TDA4863 is also depicted in the diagram: gate drive

voltage low state on page 20.