TPS54240-Q1_15 Datasheet, PDF (26/52 Pages) Texas Instruments – 3.5-V to 42-V STEP-DOWN SWIFT™ DC/DC CONVERTER WITH Eco-mode™ CONTROL

TPS54240-Q1
SLVSAQ4B – DECEMBER 2010 – REVISED SEPTEMBER 2013
V_OUT
=
Adc
´
æ
ç¹⁺
è
s
2p ´
f_Z
ö
÷
ø
V_C
æ
ç¹⁺
è
s
2p ´
f_P
ö
÷
ø
Adc = gm_ps ´ R_L
1
f_P = _{COUT ´ RL ´ 2p}
1
f_Z = _{COUT ´ RESR ´ 2p}
DETAILED DESCRIPTION (continued)
www.ti.com
(14)
(15)
(16)
(17)
Small-Signal Model for Frequency Compensation
The TPS54240-Q1 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 48. 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 48. The open-loop gain and bandwidth are modeled using the R_O
and C_O shown in Figure 48. 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.
V_O
R1
VSENSE
Vref
R2
gm_ea
COMP
Type 2A
R_O
C_O
R3 ^C2
C1
Type 2B
Type 1
R3
C2
C1
Figure 48. Types of Frequency Compensation
26
Submit Documentation Feedback
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: TPS54240-Q1