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TEA2260

SWITCH MODE POWER SUPPLY CONTROLLER

STMicroelectronics 

TEA2261/0

The magnetization state of the transformer is

checked by sensing the voltage across a winding

of the transformer (generally the same which sup-

plies the TEA2261). This is made by connecting a

resistor between this winding and the demagneti-

zation sensing input of the circuit (Pin 1).

SECURITY FUNCTIONS OF THE TEA2260 (see flowchart below)

Undervoltage Detection. This protection works in

association with the starting device “VCC switch”

(see paragraph Starting-mode - stand-by mode). If

VCC is lower than VCCstop (typically 7.4V) output

pulses are inhibited, in order to avoid wrong oper-

ation of the power supply or bad power transistor

drive.

Overvoltage Detection. If VCC exceeds VCCmax

(typically 15.7V) output pulses are inhibited. Re-

starting of the power supply is obtained by reduc-

ing VCC below VCCstop.

Current Limitation of the Power Transistor. The

current is measured by a shunt resistor. A double

threshold system is used:

– When the first threshold (VIM1) is reached, the

conduction of the power transistor is stopped un-

til the end of the period: a new conduction signal

is needed to obtain conduction again.

– Furthermore as long as the first threshold is

reached (it means during several periods), an ex-

ternal capacitor C2 is charged. When the voltage

across the capacitor reaches VC2 (typically

2.55V) the output is inhibited. This is called the

“repetitive overload protection”. If the overload

disappears before VC2 is reached, C2 is dis-

charged, so transient overloads are tolerated.

– Second current limitation threshold (VIM2). When

this threshold is reached the output of the circuit

is immediately inhibited. This protection is helpful

in case of hard overload for example to avoid the

magnetization of the transformer.

Restart of the Power Supply. After stopping due

to VC2, VIM2, VCCMax or VCCstop triggering, re-

start of the power supply can be obtained by the

normal operating of the “VCC switch” but thanks to

an integrated counter, if normal restart cannot be

obtained after three trials, the circuit is definitively

stopped. In this case it is necessary to reduce VCC

below approximately 5V to reset the circuit. From a

practical point of view, it means that the power

supply has to be temporarily disconnected from

any power source to get the restart.

7/11

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