ISL6420A Intersil, ISL6420A Datasheet - Page 18

• Manufacturer Part Number: ISL6420A
• Description: Advanced Single Synchronous Buck Pulse-Width Modulation (PWM) Controller
• Manufacturer: Intersil

ISL6420A
These equations assume linear voltage-current transitions
and do not adequately model power loss due the reverse-
recovery of the lower MOSFET’s body diode. The
gate-charge losses are dissipated by the ISL6420A and
don't heat the MOSFETs. However, large gate-charge
increases the switching interval, t
which increases the
SW
upper MOSFET switching losses. Ensure that both
MOSFETs are within their maximum junction temperature at
high ambient temperature by calculating the temperature
rise according to package thermal-resistance specifications.
A separate heatsink may be necessary depending upon
MOSFET power, package type, ambient temperature and air
flow.
Schottky Selection
Rectifier D2 is a clamp that catches the negative inductor
swing during the dead time between turning off the lower
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MOSFET and turning on the upper MOSFET. The diode must
be a Schottky type to prevent the parasitic MOSFET body
diode from conducting. It is acceptable to omit the diode and
let the body diode of the lower MOSFET clamp the negative
inductor swing, but efficiency will drop one or two percent as a
result. The diode's rated reverse breakdown voltage must be
greater than the maximum input voltage.
18
FN9169.1
October 13, 2005