Infineon ICE2HS01G User Manual

Application Note 11 2011-07-06
As discussed in section 2.2.7, the lowest switching
min
f will be seen in full load operation at
min_in
V . In this
section, how the
min
f
is actually set by the IC is explained.
Based on the definition of oscillator as in the datasheet and the external circuit around pin FREQ in
Figure 1, the minimum switching frequency will be achieved when pin SS is 2V (usually after softstart),
opto-coupler transistor is open and only
minF
R is connected to pin FREQ. For kHzf 30
min
= , the
corresponding
FREQ
R found from Figure 3 is 50kΩ. A standard value resistor of 51kΩ is selected
for
minF
R .
The maximum operation frequency can possibly be seen when maximum input voltage, say 425V, is
applied, and the converter run in no load condition (
0
=
Q ), if burst mode is disabled. The gain in this
condition can be given as:
94.01*
425
400
max_
_
min
===
nom
in
nomin
M
V
V
M [14]
From the gain equation, we get:
)0(,
)1(
)1(
),(
min
2
2
==
−
−
= QM
mF
mF
QFG [15]
The corresponding normalized frequency
max
F can be found by:
13.2
1
1
min
=
+−
=
mMm
F
Therefore
kHzkHzFf 18085*
max
== .
For 180 kHz switching frequency, the corresponding equivalent resistance
eq
R at FREQ pin is 7.5kΩ
according to Figure 3. Under no load normal operation, pin SS is already 2V after soft start, and collector
of opto-coupler transistor is pulled to ground, therefore
regeq
RRR
FMIN
//=
The
reg
R is calculated to be 8.8kΩ. A standard value resistor of 8.2kΩ is selected for the actual design.
2.3.3 Frequency setting for OCP:
Assuming the maximum rms current during over-current should be limited by the IC to 1.2 times the
maximum normal operation, i.e.
The corresponding impedance of the resonant network during over-current can be estimated as:
[16]
During over-current, the load impedence is considered to be shorted, and thereofore the impedance of
the resonant network can be calculated as:
[17]
AII
rmsinrmsocp
47.206.2*2.12.1
max___
===
Ω=== 73
47.2*
2*400
_
π
ocp
rmsin
ocp
I
V
Z
rocp
rocp
rocp
rocpocp
Cf
Lf
Cfj
LfjZ
*2
1
*2
*2*
1
*2*
π
π
π
π
−=+=

Infineon ICE2HS01G Specifications

General

Brand	Infineon
Model	ICE2HS01G
Category	Controller
Language	English