TPS54260
SLVSA86 –MARCH 2010
www.ti.com
DETAILED DESCRIPTION (continued)
V
O
Adc
VC
R
ESR
fp
R
L
gm
ps
C
OUT
fz
Figure 46. Simple Small Signal Model and Frequency Response for Peak Current Mode Control
æ
ç
è
ö
÷
ø
s
1+
1+
2p´ fZ
VOUT
= Adc ´
VC
æ
ç
è
ö
÷
ø
s
2p´ fP
(14)
(15)
Adc = gmps ´ RL
1
f
=
P
C
´R ´ 2p
L
OUT
(16)
(17)
1
f
=
Z
C
´R
´ 2p
OUT
ESR
Small Signal Model for Frequency Compensation
The TPS54260 uses a transconductance amplifier for the error amplifier and readily supports three of the
commonly-used frequency compensation circuits. Compensation circuits Type 2A, Type 2B, and Type 1 are
shown in Figure 47. Type 2 circuits most likely implemented in high bandwidth power-supply designs using low
ESR output capacitors. The Type 1 circuit is used with power-supply designs with high-ESR aluminum
electrolytic or tantalum capacitors.. Equation 18 and Equation 19 show how to relate the frequency response of
the amplifier to the small signal model in Figure 47. The open-loop gain and bandwidth are modeled using the RO
and CO shown in Figure 47. See the application section for a design example using a Type 2A network with a
low ESR output capacitor.
Equation 18 through Equation 27 are provided as a reference for those who prefer to compensate using the
preferred methods. Those who prefer to use prescribed method use the method outlined in the application
section or use switched information.
26
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