AN10907
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Application note
Rev. 1 — 28 December 2010
32 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
The adaptive non-overlap system of the TEA1613T always waits until the slope at the
half-bridge node starts. It guarantees safe/best switching of the MOSFETs in all
circumstances. In capacitive mode, it can take half the resonance period before the
resonant current changes back to the correct polarity and starts charging the half-bridge
node. To allow this relatively long waiting time, the oscillator remains in its slow charging
current mode until the half-bridge slope starts (see also
and
The MOSFET is forced to switch-on when the half-bridge slope doesn’t start at all and the
slowed-down oscillator reaches the high level.
To bring the converter from capacitive mode to inductive operation again, the oscillation
frequency is increased by the capacitive mode regulation function.
8.3.3 Capacitive Mode Regulation (CMR)
The harmful switching in capacitive mode is prevented by the adaptive non-overlap
function. However, to end the capacitive mode operation and go back to inductive mode
operation, an extra action is executed which results in the Capacitive Mode Regulation.
Capacitive mode is detected when the HB slope doesn’t start shortly (690 ns) after the
MOSFET is switched-off. When the capacitive mode is detected, the switching frequency
is quickly increased. This is realized by discharging SSHBC/EN with a high current
(1800
A) from the moment t
no-slope
= 690 ns has passed before the half-bridge slope
starts. The resultant frequency increase regulates the HBC back to the threshold between
capacitive and inductive mode.
Fig 18. Capacitive mode HBC switching
0
t
001aal442
delayed
oscillator
delayed switch-on
during capacitive mode
no HB slope
wrong polarity
GateHs
GateLs
0
V
boost
Hb
0
0
0
I
TrHbc
C
fmin
