AN10907
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© NXP B.V. 2010. All rights reserved.
Application note
Rev. 1 — 28 December 2010
57 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
9.8.2 Burst power dependent noise level
The amount of audible noise is strongly related to the amount of energy in each burst. At
low output power, the amount of energy is mainly determined by the magnetization current
of the resonant converter. The amount of transferred energy is low. To avoid problems
with audible noise, the burst mode should only be used at low power (a few watts output
power). When the transition level between normal mode and burst mode is chosen at a
higher output power, the level of audible noise is larger.
Overshoot on feedback voltage
When the output load is increased, the system reverts to normal operation. The transition
from burst mode to normal mode is based on the feedback voltage. In certain burst
conditions the feedback voltage can overshoot, keeping the system in burst mode at
higher output power levels than intended. As the power level in this situation is larger, the
amount of noise is also larger.
9.9 PFC converter and resonant converter simultaneous bursting
When in burst mode, it is beneficial to stop the PFC operation during the time that the
resonant converter is not switching. In most cases this saves extra energy consumption
by reducing switching losses from the PFC converter.
To control the external PFC, the signal from pin SNSOUT/PFCON can be used.
The behavior of the total system (PFC and resonant) in burst mode may differ from the
situation when only the resonant converter operates in burst mode. Although this may
result in good performance, there are a number of interactions.
9.9.1 PFC start delay
Depending on the PFC control system there is a certain delay in starting conversion in
burst mode. This delay is the time between SNSOUT/PFCON becoming high and the
PFC starting to switch. This results in a shorter power conversion time for the
PFC-converter compared to the resonant converter.
9.9.2 PFC output voltage variations
When bursting the PFC converter, the resonant control system determines the timing.
This may result in a situation that the PFC cannot maintain a constant output voltage. The
time during which the PFC can convert power is limited by the HBC operation and can be
too short. The result is a lower output voltage or a varying output voltage. This also has
consequences for the resonant converter as its input voltage is not the same. The working
conditions change towards a new balance.
The resonant converter must be able to remain operational during these conditions.
It is important to check that the resonant controller has not been stopped because the
input voltage provided by SNSBOOST is too low. This may cause an unacceptable
voltage decrease in the output of the resonant converter.
9.9.3 Switching between burst and normal operation
Interaction between the PFC converter and resonant converter in the burst mode can lead
to a situation whereby the system alternates between burst mode and normal mode for
certain output power conditions.
