AN10907
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2010. All rights reserved.
Application note
Rev. 1 — 28 December 2010
26 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
7.3 General details regarding MOSFET drivers
Switch on
The time to switch on is dependent upon:
•
the supply voltage for the internal driver
•
the characteristics 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
Switch off
The time to switch off is dependent upon:
•
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
(RDS-ON of the internal driver MOSFET).
Fig 13. Examples of gate circuits
001aal438
GATE
GATE
GATE
GATE
