FAN5092MTC Datasheet, PDF (17/20 Pages) Fairchild Semiconductor – High Current System Voltage Buck Converter

PRODUCT SPECIFICATION
FAN5092
ESR. The only type of aluminum capacitor used should be
those that have an ESR rated at 100kHz. Consult Application
Bulletin AB-14 for detailed information on output capacitor
selection.
For higher frequency applications, particularly those running
the FAN5092 oscillator at >1MHz, Oscon or ceramic capaci-
tors may be considered. They have much smaller ESR than
comparable electrolytics, but also much smaller capacitance.
The output capacitance should also include a number of
small value ceramic capacitors placed as close as possible to
the processor; 0.1µF and 0.01µF are recommended values.
Input Filter
The DC-DC converter design may include an input inductor
between the system main supply and the converter input as
shown in Figure 4. This inductor serves to isolate the main
supply from the noise in the switching portion of the DC-DC
converter, and to limit the inrush current into the input capac-
itors during power up. A value of 1.3µH is recommended.
for the four slice FAN5092, where DC is the duty cycle,
DC = Vout / Vin. Capacitor ripple current rating is a function
of temperature, and so the manufacturer should be contacted
to find out the ripple current rating at the expected opera-
tional temperature. For details on the design of an input filter,
refer to Applications Bulletin AB-16.
+12V
1.3 µH
Vin
1000µF, 16V
Electrolytic
Figure 4. Input Filter
Design Considerations and Component
Selection
Additional information on design and component selection
may be found in Fairchild’s Application Note 59.
It is necessary to have some low ESR capacitors at the input
to the converter. These capacitors deliver current when the
high side MOSFET switches on. Because of the interleaving,
the number of such capacitors required is greatly reduced
from that required for a single-slice buck converter. Figure 5
shows 3 x 1000µF, but the exact number required will vary
with the output voltage and current, according to the formula
I_rms = ^I--^o-₄--^u---^t 4DC – 16DC²
REV. 1.0.7 6/20/02
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