CoolSET™-F3
Functional Description
3.2
Power Management
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.
VCC
Drain
Startup Cell
3.1
Introduction
CoolSET™-F3 is the further development of the
CoolSET™-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 CoolSET™-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 Vout is
minimized. Vout is further on well controlled in this
mode.
Depl-CoolMOS™
Power Management
Undervoltage Lockout
15V
Internal Bias
8.5V
6.5V
Voltage
Reference
Auto Restart Mode
Active Burst 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.
T1
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. This Startup
Cell is part of the integrated Depl-CoolMOS™. The
external startup resistor is no longer necessary as this
Startup Cell is connected to the Drain. Power losses
are therefore reduced. This increases the efficiency
under light load conditions drastically.
SoftS
Power Management
Figure 6
The Undervoltage Lockout monitors the external
supply voltage VVCC. When the SMPS is plugged to the
main line the internal Startup Cell is biased and starts
to charge the external capacitor CVCC which is
connected to the VCC pin. This VCC charge current
which is provided by the Startup Cell from the Drain pin
is 1.05mA. When VVCC exceeds the on-threshold
VCCon=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 Drain voltage. 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 VVCC falls below 8.5V.
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 maximum current consumption before the
controller is activated is about 160µA.
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
When VVCC falls below the off-threshold VCCoff=8.5V the
internal reference is switched off and the Power Down
reset let T1 discharging the soft-start capacitor CSoftS at
pin SoftS. Thus it is ensured that at every startup cycle
the voltage ramp at pin SoftS starts at zero.
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 the secondary diode.
The internal Voltage Reference is switched off if Auto
Restart Mode is entered. The current consumption is
then reduced to 300µA.
Version 1.3
11
15 Sep 2004
INFINEON [ Infineon ]
