ICE3BS02L Datasheet, PDF (14/21 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 500V Startup Cell and Latched off Mode

F3
ICE3BS02L
Functional Description
outside the operating range > 4.8V, e.g. when Open Loop
happens. This means any small voltage overshoots of V_VCC
during normal operating can not start the Latched Off Mode.
The internal Voltage Reference is switched off once Latched
Off Mode is entered in order to reduce the current
consumption of the IC as much as possible. Latched Off
Mode can only be reset by decreasing V_VCC < 6V. In this
stage, only the UVLO is working which controls the Startup
Cell by switching on/off at V_VCCon/V_VCCoff. During this
phase, the average current consumption is only 300µA. As
there is no longer a self- supply by the auxiliary winding,
VCC drops. The Undervoltage Lockout switches on the
integrated Startup Cell when VCC falls below 8.5V. The
Startup Cell is switched off again when VCC has exceeded
15V. Once the Latched Off Mode was entered, there is no
Start Up Phase after VCC has exceeded the switch-on level
of the Undervoltage Lockout. Therefore VCC changes
between the switch-on and switch-off levels of the
Undervoltage Lockout with a saw tooth shape (see Figure
18).
V_VCC
15V
3.6.3.2 Auto Restart Mode
SoftS
6.5V
5kΩ ^RSoftS
4.4V
1
S1
G2
C3
5.4V
4.8V
&
C4
G5
FB
Voltage
Reference
Auto
Restart
Mode
Control Unit
8.5V
I_VCCStart
t
1.05mA
V_OUT
t
Figure 18 Signals in Latched Off Mode
The Thermal Shutdown block monitors the junction
temperature of the IC. After detecting a junction temperature
higher than 140°C, Latched Off Mode is entered.
The signals coming from the temperature detection and VCC
overvoltage detection are fed into a spike blanking with a
time constant of 8.0µs to ensure system reliability.
Furthermore, a short winding or short diode on the secondary
side can be detected by the comparator C11 which is in
parallel to the propagation delay compensated current limit
comparator C10. In normal operating mode comparator C10
keeps the maximum level of the CS signal at 1V. If there is
a failure such as short winding or short diode, C10 is no
longer able to limit the CS signal at 1V. C11 detects then the
over current and enters immediately the Latched Off Mode
to keep the SMPS in a safe stage.
Figure 19 Auto Restart Mode
In case of Overload or Open Loop, FB exceeds 4.8V which
will be observed by C4. At this time S1 is released that V_SoftS
can increase. If V_SoftS exceeds 5.4V which is observed by C3,
Auto Restart Mode is entered as both inputs of the gate G5
are high. In combining the FB and SoftS signals, there is a
blanking window generated which prevents the system to
enter Auto Restart Mode due to large load jumps. This time
window is the same as for the Active Burst Mode and can
therefore be adjusted by the external C_SoftS.
In case of VCC undervoltage, the IC enters into the Auto
Restart Mode and starts a new startup cycle.
Short Optocoupler also leads to VCC undervoltage as there
is no self supply after activating the internal reference and
bias.
In contrast to the Latched Off Mode, there is always a Startup
Phase with switching cycles in Auto Restart Mode. After this
Start Up Phase, the conditions are again checked whether the
failure mode is still present. Normal operation is resumed
once the failure mode is removed that had caused the Auto
Restart Mode.
Version 1.1
14
28 Sep 2005