InnoSwitch-CH
ꢈꢅ-ꢂꢉ ꢁ ꢃ
ꢀꢁ ≡ ꢀꢂꢁ
ꢀ
t
ꢃ ꢄ ꢅꢆꢇS
ꢁꢌiꢕꢓꢌꢖ
ꢈꢅ-ꢂꢉ ꢁ ꢃ
ꢂ ꢁ ꢃ
t
Sꢎconꢍꢓꢌꢖ
ꢈꢓꢉ ꢂiꢐcontinꢑoꢑꢐꢒ ꢀꢁ ꢔ ꢅ
ꢃ ꢄ ꢅꢆꢇS
ꢁꢌiꢕꢓꢌꢖ
ꢈꢅ-ꢂꢉ ꢁ ꢃ ꢄ t
ꢂ ꢁ ꢃ
Sꢎconꢍꢓꢌꢖ
ꢈꢊꢉ ꢋoꢌꢍꢎꢌꢏinꢎ ꢂiꢐcontinꢑoꢑꢐꢆContinꢑoꢑꢐꢒ ꢀꢁ ꢄ ꢅ
ꢂꢃꢄꢅꢆ7ꢇꢄ10ꢈ11ꢉ
Figure 22. Discontinuous Mode Current Waveform, KP ≥1.
The following minimum set of tests is strongly recommended:
Maximum Operating Flux Density, BM (Gauss)
A maximum value of 3000 Gauss during normal operation is recom-
mended to limit the maximum flux density under start-up and output
short-circuit. Under these conditions the output voltage is low and
little reset of the transformer occurs during the MOSFET off-time.
This allows the transformer flux density to staircase above the normal
operating level. A value of 3000 Gauss at the peak current limit of
the selected device together with the built-in protection features of
InnoSwitch-CH IC provides sufficient margin to prevent core
saturation under start-up or output short-circuit conditions.
1. Maximum drain voltage – Verify that VDS does not exceed 600 V
at highest input voltage and peak (overload) output power. The
50 V margin to the 650 V BVDSS specification gives margin for
design variation.
2. Maximum drain current – At maximum ambient temperature,
maximum input voltage and peak output (overload) power, verify
drain current waveforms for any signs of transformer saturation
and excessive leading edge current spikes at start-up. Repeat
under steady-state conditions and verify that the leading edge
current spike event is below ILIMIT(MIN) at the end of the tLEB(MIN)
Under all conditions, the maximum drain current should be below
the specified absolute maximum ratings.
.
Transformer Primary Inductance, (LP)
Once the lowest operating voltage and the required VOR are deter-
mined, transformer primary inductance can be calculated. Care
should be taken to ensure that the selected inductance value does
not violate the maximum duty cycle specification in the data sheet of
the InnoSwitch-CH IC. The PIXls design spreadsheet which is part of
the free PI Expert suite can be used to assist in designing the
transformer.
3. Thermal Check – At specified maximum output power, minimum
input voltage and maximum ambient temperature, verify that the
temperature specifications are not exceeded for InnoSwitch-CH
IC, transformer, output SR MOSFET, and output capacitors.
Enough thermal margin should be allowed for part-to-part
variation of the RDS(ON) of InnoSwitch-CH IC as specified in the
data sheet.
Quick Design Checklist
As with any power supply design, all InnoSwitch-CH designs should
be verified on the bench to make sure that component specifications
are not exceeded under worst-case conditions.
Under low-line, maximum power, a maximum InnoSwitch-CH SOURCE
pin temperature of 110 °C is recommended to allow for these variations.
15
Rev. J 10/17
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