ICE3AS02_05 Datasheet, PDF (8/22 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 500V Startup Cell

F3
ICE3AS02 / ICE3AS02G / ICE3BS02 / ICE3BS02G
Functional Description
3 Functional Description
All values which are used in the functional description are _3.2
typical values. For calculating the worst cases the min/max
Power Management
values which can be found in section 4 Electrical
VCC
HV
Characteristics have to be considered.
Startup Cell
3.1
Introduction
The F3 is the further development of the F2 to meet the
requirements for the lowest Standby Power at minimum load
and no load conditions. A new fully integrated Standby
Power concept is implemented into the IC in order to keep
the application design easy. Compared to F2 no further
external parts are needed to achieve the lowest Standby
Power. An intelligent Active Burst Mode is used for this
Standby Mode. After entering this mode there is still a full
control of the power conversion by the secondary side via the
same optocoupler that is used for the normal PWM control.
The response on load jumps is optimized. The voltage ripple
on V_out is minimized. V_out is further on well controlled in this
mode.
The usually external connected RC-filter in the feedback line
after the optocoupler is integrated in the IC to reduce the
external part count.
Furthermore a high voltage startup cell is integrated into the
IC which is switched off once the Undervoltage Lockout on-
threshold of 15V is exceeded. The external startup resistor is
no longer necessary. Power losses are therefore reduced.
This increases the efficiency under light load conditions
drastically.
The Soft-Start capacitor is also used for providing an
adjustable blanking window for high load jumps. During this
time window the overload detection is disabled. With this
concept no further external components are necessary to
adjust the blanking window.
An Auto Restart Mode is implemented in the IC to reduce the
average power conversion in the event of malfunction or
unsafe operating condition in the SMPS system. This feature
increases the system’s robustness and safety which would
otherwise lead to a destruction of the SMPS. Once the
malfunction is removed, normal operation is automatically
initiated after the next Start Up Phase.
The internal precise peak current limitation reduces the costs
for the transformer and the secondary diode. The influence
of the change in the input voltage on the power limitation can
be avoided together with the integrated Propagation Delay
Compensation. Therefore the maximum power is nearly
independent on the input voltage which is required for wide
range SMPS. There is no need for an extra over-sizing of the
SMPS, e.g. the transformer or PowerMOS.
Undervoltage Lockout
15V
8.5V
Power Management
Internal Bias
6.5V
Voltage
Reference
Auto Restart Mode
T1
Active Burst Mode
SoftS
Figure 4 Power Management
The Undervoltage Lockout monitors the external supply
voltage V_VCC. When the SMPS is plugged to the main line
the internal Startup Cell is biased and starts to charge the
external capacitor C_VCC which is connected to the VCC pin.
This VCC charge current which is provided by the Startup
Cell from the HV pin is 1.05mA. When V_VCC exceeds the on-
threshold V_CCon=15V the internal voltage reference and bias
circuit are switched on. Then the Startup Cell is switched off
by the Undervoltage Lockout and therefore no power losses
present due to the connection of the Startup Cell to the bus
voltage (HV). To avoid uncontrolled ringing at switch-on a
hysteresis is implemented. The switch-off of the controller
can only take place after Active Mode was entered and V_VCC
falls below 8.5V.
The maximum current consumption before the controller is
activated is about 160µA.
When V_VCC falls below the off-threshold V_CCoff=8.5V the
internal reference is switched off and the Power Down reset
let T1 discharging the soft-start capacitor C_SoftS at pin SoftS.
Thus it is ensured that at every startup cycle the voltage ramp
at pin SoftS starts at zero.
The internal Voltage Reference is switched off if Auto
Restart Mode is entered. The current consumption is then
reduced to 300µA.
Once the malfunction condition is removed, this block will
then turn back on. The recovery from Auto Restart Mode
does not require disconnecting the SMPS from the AC line.
Version 1.2
8
02 Sep 2005