Datasheet

0.5 1 1.5 2
0
0.5
1
1.5
2
0.1
n
f
M
5=
e
Q
2=
e
Q
1=
e
Q
5.0=
e
Q
2.0=
e
Q
1.0=
e
Q
0.5 1 1.5 2
0
0.5
1
1.5
2
0.1
n
f
M
5=
e
Q
2=
e
Q
1=
e
Q
5.0=
e
Q
2.0=
e
Q
1.0=
e
Q
0.5 1 1.5 2
0
0.5
1
1.5
2
0.1
n
f
M
5=
e
Q
2=
e
Q
1=
e
Q
5.0=
e
Q
2.0=
e
Q
1.0=
e
Q
0.5 1 1.5 2
0
0.5
1
1.5
2
0.1
n
f
M
5=
e
Q
2=
e
Q
1=
e
Q
5.0=
e
Q
2.0=
e
Q
1.0=
e
Q
UCC25600
SLUS846B –SEPTEMBER 2008– REVISED JULY 2011 www.ti.com
From Equation 8, when switching frequency is equal to resonant frequency, f
n
= 1 and converter voltage gain is
equal to 1. Converter gain at different loads and inductor ratio conditions are shown in Figure 14 through
Figure 17.
M M
vs vs
ƒ
n
ƒ
n
Figure 14. Figure 15.
M M
vs vs
ƒ
n
ƒ
n
Figure 16. Figure 17.
Based on its theory of operation the LLC resonant converter is controlled through Pulse Frequency Modulation
(PFM). The output voltage is regulated by adjusting the switching frequency according to the input and output
conditions. Optimal efficiency is achieved at the nominal input voltage by setting the switching frequency close to
the resonant frequency. When the input voltage droops low the switching frequency is decreased to boost the
gain and maintain regulation.
The UCC25600 resonant half-bridge controller uses variable switching frequency control to adjust the resonant
tank impedance and regulate output voltage. This 8-pin package device integrates the critical functions for
optimizing the system performance while greatly simplifying the design and layout.
12 Copyright © 2008–2011, Texas Instruments Incorporated