TEA2260 - TEA2261
SECURITY FUNCTIONS OF THE TEA2261 (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.
external capacitor C2 is charged. When the
voltage across the capacitor reaches VC2 (typi-
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.
- 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
- 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.
V
CCstop 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
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
- 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 se-
quency from VCCstop to VCCstart . After stopping
due to VC2 threshold reaching, the circuit is de-
finitively 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.
SECURITY FLOW-CHART (TEA2261)
S.M.P.S.
starting
First
Y
threshold reached
VIM1
Second
threshold reached
VIM2
N
N
VCCmax
reached
Y
Pulse by pulse current
limiting C2 charged
Y
C2 charged
S.M.P.S. stopped
N
Normal operating
C2 discharged
Y
VC2 < 2.6V
N
Y
VC2 < 2.6V
N
Definitive
stopping
Reset C2
discharged
N
Y
7/9
STMICROELECTRONICS [ ST ]
