CoolSET™-F2
Functional Description
3
3.1
Functional Description
Power Management
Main Line (100V-380V)
3.2
Improved Current Mode
Soft-Start Comparator
PWM-Latch
R
Primary Winding
R
Start-Up
FB
PWM Comparator
Q
Driver
S
Q
C
VCC
VCC
Power Management
Undervoltage
Lockout
13.5V
8.5V
Power-Down
Reset
Voltage
Reference
Power-Up
Reset
R
Q
PWM-Latch
6.5V
SoftS
S
Q
6.5V
5.3V
4.8V
4.0V
Internal
Bias
0.8V
PWM OP
x3.65
Improved
Current Mode
Figure 7
Current Mode
Isense
R
Soft-Start
Error-Latch
Soft-Start Comparator
Current Mode means that the duty cycle is controlled
by the slope of the primary current. This is done by
comparison the FB signal with the amplified current
sense signal.
Amplified Current Signal
C
Soft-Start
T1
Error-Detection
FB
Figure 6
Power Management
The Undervoltage Lockout monitors the external
supply voltage V
VCC
. In case the IC is inactive the
current consumption is max. 55µA. When the SMPS is
plugged to the main line the current through R
Start-up
charges the external Capacitor C
VCC
. When V
VCC
exceeds the on-threshold V
CCon
=13.5V the internal bias
circuit and the voltage reference are switched on. After
that the internal bandgap generates a reference
voltage V
REF
=6.5V to supply the internal circuits. To
avoid uncontrolled ringing at switch-on a hysteresis is
implemented which means that switch-off is only after
active mode when Vcc falls below 8.5V.
In case of switch-on a Power Up Reset is done by
resetting the internal error-latch in the protection unit.
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
Soft-Start
at pin SoftS. Thus it is ensured that at every switch-on
the voltage ramp at pin SoftS starts at zero.
0.8V
Driver
t
T
on
t
Figure 8
Pulse Width Modulation
In case the amplified current sense signal exceeds the
FB signal the on-time T
on
of the driver is finished by
resetting the PWM-Latch (see Figure 8).
The primary current is sensed by the external series
resistor R
Sense
inserted in the source of the integrated
CoolMOS™. By means of Current Mode regulation, the
Version 2.8
10
30 Aug 2011
INFINEON [ INFINEON TECHNOLOGIES AG ]
