AN10907
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Application note
Rev. 1 — 28 December 2010
31 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
and the other MOSFET is switched-on. In this way the non-overlap time is automatically
adjusted to the best value providing the lowest switching loss, even if the HB transition
cannot be fully completed.
The non-overlap time depends on the HB slope, but has an upper and lower time limit. An
integrated minimum non-overlap time (160 ns) prevents accidental cross conduction in all
conditions. The maximum non-overlap time is limited to the charging time of the oscillator.
If the HB slope takes more time than the charging of the oscillator (25 % of HB switching
period) the MOSFET is forced to switch on. In this case the MOSFET is not soft-switching.
This limitation of the maximum non-overlap time ensures that at very high switching
frequency the on-time of the MOSFET is at least 25 % of the HB switching period.
8.3.2 Capacitive mode
During error conditions (e.g. output short-circuit, load pulse too high) or special start-up
conditions, the switching frequency can become lower than the resonance frequency. The
resonant tank then has a capacitive impedance. In capacitive mode the HB slope doesn’t
start after the MOSFET has switched off. It is not preferred to just switch on the other
MOSFET. The lack of soft-switching increases dissipation in the MOSFETs. The
conducting body diode in the MOSFET at the switching moment can damage the device
very quickly.
Fig 17. Adaptive non-overlap switching during normal operating conditions
fast HB slope
V
boost
Hb
GateLs
GateHs
0
slow HB slope
incomplete HB slope
t
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