ICE2A280 Infineon Technologies Corporation, ICE2A280 Datasheet - Page 10

• Manufacturer Part Number: ICE2A280
• Manufacturer: Infineon Technologies Corporation

Figure 11 Start Up Phase
3.4
3.4.1
The oscillator generates a frequency f
resistor, a capacitor and a current source and current
sink which determine the frequency are integrated. The
charging and discharging current of the implemented
oscillator capacitor are internally trimmed, in order to
achieve a very accurate switching frequency. The ratio
of controlled charge to discharge current is adjusted to
reach a max. duty cycle limitation of D
3.4.2
The frequency of the oscillator is depending on the
voltage at pin FB. The dependence is shown in Figure
12. This feature allows a power supply to operate at
lower frequency at light loads thus lowering the
switching losses while maintaining good cross
regulation performance and low output ripple. In case
of low power the power consumption of the whole
SMPS can now be reduced very effective. The minimal
reachable frequency is limited to 21.5 kHz to avoid
audible noise in any case.
Datasheet
5 .3 V
4 .8 V
V
O U T
V
V
V
F B
S o ftS
O U T
Oscillator and Frequency
Reduction
Oscillator
Frequency Reduction
T
T
S ta rt-U p
S oft-S ta rt
switch
max
=0.72.
= 100kHz. A
t
t
t
10
Figure 12
3.5
There is a cycle by cycle current limiting realised by the
Current-Limit Comparator to provide an overcurrent
detection. The source current of the integrated
CoolMOS
R
transformed to a sense voltage V
voltage V
V
off the gate drive. To prevent the Current Limiting from
distortions caused by leading edge spikes a Leading
Edge Blanking is integrated at the Current Sense.
Furthermore a Propagation Delay Compensation is
added to support the immedeate shut down of the
CoolMOS™ in case of overcurrent.
3.5.1
Figure 13
Each time when CoolMOS™ is switched on a leading
spike
capacitances and secondary-side rectifier reverse
recovery time. To avoid a premature termination of the
switching pulse this spike is blanked out with a time
constant of t
the Current-Limit Comparator cannot switch off the
gate drive.
csth
Sense
V
c s th
kHz
21,5
100
V
0,9
the Current-Limit-Comparator immediately turns
65
S en s e
. By means of R
1,0
is
Sense
TM
Current Limiting
Leading Edge Blanking
1,1
Frequency Dependence
Leading Edge Blanking
generated
LEB
is sensed via an external sense resistor
exceeds the internal threshold voltage
1,2
= 220ns. During that time the output of
1,3
Functional Description
t
1,4
L E B
due
Sense
V
ICE2A165/265/365
1,5
= 22 0 ns
FB
1,6
to
the source current is
CoolSET™-F2
ICE2A180/280
1,7
September 2001
the
Sense
1,8
. When the
primary-side
1,9
2
t
V