Datasheet

Vref
V
O
R1
R3
C1
C2
R2
C
O
R
O
gm
ea
COMP
FB
Type 2A Type 2B Type 1
C2
R3
C1
Z
OUT ESR
1
C R 2
=
´ ´ p
f
P
OUT L
1
f
C R 2
=
´ ´ p
ps L
Adc = gm R´
Z
OUT
C
P
s
1
2
V
Adc
V
s
1
2
æ ö
+
ç ÷
p ´
è ø
= ´
æ ö
+
ç ÷
p ´
è ø
f
f
TPS54560
SLVSBN0A –MARCH 2013–REVISED MARCH 2014 www.ti.com
Feature Description (continued)
(10)
(11)
(12)
(13)
8.3.16 Small Signal Model for Frequency Compensation
The TPS54560 uses a transconductance amplifier for the error amplifier and supports three of the commonly-
used frequency compensation circuits. Compensation circuits Type 2A, Type 2B, and Type 1 are shown in
Figure 33. Type 2 circuits are typically 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 14 and Equation 15 relate the frequency response of the amplifier to the small
signal model in Figure 33. The open-loop gain and bandwidth are modeled using the R
O
and C
O
shown in
Figure 33. See the application section for a design example using a Type 2A network with a low ESR output
capacitor.
Equation 14 through Equation 23 are provided as a reference. An alternative is to use WEBENCH software tools
to create a design based on the power supply requirements.
Figure 33. Types of Frequency Compensation
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