AN10881
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Application note
Rev. 2 — 26 September 2011
31 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
6.4 General subjects on MOSFET drivers
6.4.1 Switch on
The time to switch on depends on:
•
The supply voltage for the internal driver
•
The characteristic of the internal driver
•
The gate capacitance to be charged
•
The gate threshold voltage for the MOSFET to switch on
•
The external circuit to the gate
6.4.2 Switch off
The time to switch off depends on:
•
The characteristic of the internal driver
•
The gate capacitance to be discharged
•
The voltage on the gate just before discharge
•
The gate threshold voltage for the MOSFET to switch off
•
The external circuit to the gate
Because the timing for switching off the MOSFET is more critical than switching it on, the
internal driver can sink more current than it can source. At higher frequencies and/or short
on-time, timing becomes more critical for correct switching. Sometimes a compromise
must be made between fast switching and EMI effects. A gate circuit between the driver
output and the gate can be used to optimize the switching behavior.
Switching the MOSFETs on and off by the drivers can be approximated by alternating
charge and discharge of a (gate-source) capacitance of the MOSFET through a resistor
(R
DSon
of the internal driver MOSFET).
Fig 14. Gate circuits examples
001aal025
GATEPFC
GATEPFC
GATEPFC
GATEPFC
d.
c.
b.
a.
