Power integrations InnoSwitch3 Application Note page 7

AN-72
Step 3 – Worst-Case Electrical Parameters
Enter: FSWITCHING_MAX, VOR and LPRIMARY_TOL, or VMIN
WORST CASE ELECTRICAL
33 PARAMETERS
34 FSWITCHING_MAX
35 VOR
36 VMIN
37 KP
38 MODE_OPERATION
39 DUTYCYCLE
40 TIME_ON
41 TIME_OFF
42 LPRIMARY_MIN
43 LPRIMARY_TYP
44 LPRIMARY_TOL
45 LPRIMARY_MAX
46
47 PRIMARY CURRENT
48 IPEAK_PRIMARY
49 IPEDESTAL_PRIMARY
50 IAVG_PRIMARY
51 IRIPPLE_PRIMARY
52 IRMS_PRIMARY
53
54 SECONDARY CURRENT
55 IPEAK_SECONDARY
56 IPEDESTAL_SECONDARY
57 IRMS_SECONDARY
Figure 4. Worst-Case Electrical Parameters Section of InnoSwitch3-CE Design Spreadsheet with Gray Override Cells.
Switching Frequency, FSWITCHING_MAX (Hz)
This parameter is the switching frequency at full load at minimum
rectified AC input voltage. The maximum switching frequency of
InnoSwitch3 in normal operation is 100 kHz, and the typical overload
detection frequency of is 110 kHz. In normal operating condition, the
switching frequency at full load should not be close to the overload
detection frequency.
The programmable switching frequency range is 25 to 95 kHz, but it
should be continued that the average frequency accounting for
primary inductance and peak current tolerances does not result in
average frequency higher than 110 kHz as this will trigger auto-
restart due to overload. Pushing frequency higher to reduce
transformer size is advisable, but Table 5 provides the suggested
frequency based on the size of the internal high-voltage MOSFET, and
represents the best compromise to balance overall device losses (i.e.
conduction and switching losses).
Reflected Output Voltage, VOR (V)
This parameter is the secondary winding voltage during the diode /
Synchronous Rectifier MOSFET (SR FET) conduction-time reflected
back to the primary through the turns ratio of the transformer. Table
6 provides suggested values of VOR. VOR can be adjusted to achieve
a design that does not violate design rules for the transformer and
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80000
3.0
Maximum switching frequency at full load and
80000 Hz valley of the rectified minimum AC input voltage
Seconday voltage reflected to the primary when
65.0 V the primary MOSFET turns off
Valley of the rectified minimum AC input voltage
85.95 V at full power
Measure of continuous/discontinuous mode of
0.66 operation
CCM Mode of operation
0.433 Primary MOSFET duty cycle
7.46 us Primary MOSFET on-time
7.09 us Primary MOSFET off-time
805.6 uH Minimum primary inductance
830.5 uH Typical primary inductance
3.0 % Primary inductance tolerance
855.4 uH Maximum primary inductance
0.95 A Primary MOSFET peak currrent
0.30 A Primary MOSFET current pedestal
0.25 A Primary MOSFET average current
0.76 A Primary MOSFET ripple current
0.41 A Primary MOSFET RMS current
12.24 A Secondary winding peak current
3.79 A Secondary winding current pedestal
6.44 A Secondary winding RMS current
InnoSwitch3 Family
INN3xx2C and
INN3xx3C
INN3xx4C and
INN3xx5C
INN3xx6C
INN3xx7C
INN3xx8C
Table 5. Suggested Maximum Switching Frequency.
SR FET while simultaneously achieving sufficiently low Drain-Source
voltage of the primary side MOSFET. VOR can be adjusted as
necessary to ensure that no warnings in the spreadsheet are
triggered. For design optimization purposes, the following factors
should be considered,
• Higher VOR allows increased power delivery at VMIN, which
minimizes the value of the input capacitor and maximizes power
delivery from a given.
Application Note
Maximum Switching Frequency
85 - 90 kHz
80 kHz
75 kHz
70 kHz
65 kHz
Rev. A 10/18
7