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TEA2260

SWITCH MODE POWER SUPPLY CONTROLLER

STMicroelectronics 

TEA2261/0

SECURITY FUNCTIONS OF THE TEA2261 (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 and

the external capacitor C2 is charged as long as

VCC is higher than VCC stop. Restarting of the

power supply is obtained by reducing VCC below

VCCstop except if the voltage across C2 reaches

VC2 (typically 2.55V) (refer to “Restart of the power

supply” paragraph).In this last case, the circuit is

definitively stopped.

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 VIM2, VCCMax or VCCstop triggering, restart of

the power supply can be obtained by the normal

operating of the “VCC switch” VCC switch sequency

from VCCstop to VCCstart. After stopping due to

VC2 threshold reaching, 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.

Figure 6. Security Flowchart (TEA2260)

S.M.P.S.

starting

First

threshold reached

Y

VIM1

N

VCCmax

Y

reached

N

Normal operating

C2 discharged

Second

threshold reached

N

VIM2

Y

C2 charged

S.M.P.S. stopped

VC2 < 2.6V

Y

N

Definitive

stopping

Pulse by pulse current

limiting C2 charged

VC2 < 2.6V

Y

N

Reset C2

N

discharged

Y

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