TEA2260 - TEA2261
SECURITY FUNCTIONS OF THE TEA2260 (see flow-chart below)
- Undervoltage detection. This protection works
in association with the starting device "VCC
switch" (see paragraph Starting-mode - standby
mode). If VCC is lower than VCCstop (typically
7.4V) output pulses are inhibited, in order to avoid
wrong operation 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.
cally 2.55V) the output is inhibited. This is called
the "repetitive overload protection". If the over-
load diseappears before VC2 is reached, C2 is
discharged, so transient overloads are toler-
ated.
- Second current limitation threshold (VIM2).
When this threshold is reached the output of the
circuit is immediatly inhibited. This protection is
helpfull 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 integrted counter, if normal restart cannot
be obtained after three trials, the circuit is defini-
tively 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 dis-
connected from any power source to get the
restart.
- 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
until 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
external capacitor C2 is charged. When the
voltage across the capacitor reaches VC2 (typi-
SECURITY FLOW-CHART (TEA2260)
S.M.P.S.
starting
First
Y
threshold reached
VIM1
Second
Y
N
threshold reached
VIM2
N
Pulse by pulse current
limiting C2 charged
Y
VC2 < 2.6V
VCCmax
reached
Y
N
S.M.P.S. stopping
V
CC stop reached
N
N = N + 1
Normal operating
C2 discharged
Restart
number = 3
N
Y
Reset C2
discharged
N
Definitive
stopping
Y
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STMICROELECTRONICS [ ST ]
