ICE3BRXX65J(Z)(G)
Application Note
15
2010-06-20
6.6 Protection
Features
The IC provides several protection features which lead to the Auto Restart Protection Mode. The following
table shows the conditions of the system failure and the associate protection mode.
Protection function
Failure condition
Protection Mode
Vcc Over-voltage
1. Vcc > 25.5V or
2. Vcc > 20.5V & FB > 4.0V & during soft start period
Auto Restart
Over-temperature
(controller junction)
T
J
> 130°C
Auto Restart
Over-load / Open loop
V
FB
> 4.0V and V
BA
> 4.0V
(Blanking time counted from charging V
BA
from 0.9V to
4.0V )
Auto Restart
Vcc Under-voltage / short
Opto-coupler
Vcc < 10.5V
Auto Restart
Auto-restart enable
V
BA
< 0.33V
Auto Restart
Table 1 Protection functions and failure conditions
The 25.5V OVP protection is inactivated during burst mode so that it can achieve lower standby power
performance.
6.6.1
Auto Restart Protection Mode
When the failure condition meets the auto restart protection mode, the IC will go into auto-restart. The
switching pulse will stop. Then the Vcc voltage will drop. When the Vcc voltage drops to 10.5V, the startup
cell will turn on again. The Vcc voltage is then charged up. When it hits 18V, the IC will turn on and the
startup cell will turn off. It would then start the startup phase with soft start. After the startup phase the failure
condition is checked to determine whether the fault persists. If the fault is removed, it will go to normal
operation. Otherwise, the IC will repeat the auto restart protection and the switching pulse stop again.
Figure 15 shows the switching waveform of the V
CC
and the feedback voltage V
FB
when the output is
overloaded by shorting the outputs. The IC is turned on at V
CC
= 18V. After going through the startup phase,
IC is off again due to the presence of the fault. V
CC
is discharged until 10.5V. Then, the Startup Cell is
activated again to charge up capacitor at V
CC
that initiates another restart cycle.
Channel 1; C1 : Drain-Source Voltage (V
DS
)
Channel 2; C2 : Supply Voltage (V
CC
)
Channel 3; C3 : Feedback Voltage ( V
FB
)
Channel 4; C4 : BA voltage ( V
BA
)
System enters auto restart mode when output
voltage short circuit @ Vin=85Vac
Figure 15 Auto Restart Mode
V
DS
Vcc
V
FB
V
BA