AN10907
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© NXP B.V. 2010. All rights reserved.
Application note
Rev. 1 — 28 December 2010
55 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
9.6 Output power - operating frequency characteristics
As can be concluded from
, the design choice, for a certain SNSFB voltage at
which bursting starts, is critical. With this kind of characteristic there is a risk that, due to
spread, the system can either remain in burst mode or never reach burst-mode operation
at all. The dimensioning of the LLC can be made more suitable for burst mode. The
standard approach is to design the system in such a way that it cannot regulate to
no-load, even at the highest frequency. During the lowest loads, the required frequency
for regulation must become infinite. Because the characteristic is much steeper for low
output power, a voltage level can then be chosen easily to make sure that burst mode is
activated at the lowest load and that the remaining load conditions operates in normal
mode. The burst mode now enables the system to operate at no-load.
Fig 42. Typical SNSFB voltage-to-output power characteristic of a converter without
burst mode functionality
P
o
(W)
0
250
200
100
150
50
001aal465
5.4
5.6
5.2
5.8
6.0
SNSFB
(V)
5.0
Fig 43. Example of SNSFB and frequency as functions of output power characteristics (normal mode) adapted
for easy implementation of burst mode comparator level detection
P
o
(W)
0
100
80
40
60
20
4.8
5.6
6.2
SNSFB
(V)
4.0
P
o
(W)
0
100
80
40
60
20
001aal466
120
160
200
f
(kHz)
80
