ICE3AS02 Datasheet, PDF (8/23 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 typical values. For calculating the worst cases the
min/max values which can be found in section 4
Electrical Characteristics have to be considered.
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.
3.2
Power Management
VCC
HV
Startup Cell
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.
Version 1.1
8
21 May 2004