S-8337AAAA-P8T1G Datasheet, PDF (19/51 Pages) Seiko Instruments Inc – SWITCHING REGULATOR CONTROLLER

STEP-UP, 1.2 MHz HIGH-FREQUENCY, PWM CONTROL SWITCHING REGULATOR CONTROLLER
Rev.4.0_01
S-8337/8338 Series
4. 2 Enhancement MOS FET type
Use an Nch power MOS FET. For high efficiency, using a MOS FET with a low ON resistance
(RON) and small input capacitance (CISS) is ideal, however, ON resistance and input capacitance
generally share a trade-off relationship. The ON resistance is efficient in a range in which the
output current is relatively great during low-frequency switching, and the input capacitance is
efficient in a range in which the output current is middling during high-frequency switching. Select
a MOS FET whose ON resistance and input capacitance are optimal depending on the usage
conditions.
The input voltage (VIN) is supplied for the gate voltage of the MOS FET, so select a MOS FET with
a gate withstanding voltage that is equal to the maximum usage value of the input voltage or
higher and a drain withstanding voltage that is equal to the amount of the output voltage (VOUT)
and diode voltage (VD) or higher.
If a MOS FET with a threshold that is near the UVLO detection voltage is used, a large current
may flow, stopping the output voltage from rising and possibly generating heat in the worst case.
Select a MOS FET with a threshold that is sufficiently lower than the UVLO detection voltage
value.
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