TPS57140-Q1 Datasheet, PDF (35/49 Pages) Texas Instruments – 1.5-A 42-V STEP-DOWN SWIFT™ DC/DC CONVERTER WITH Eco-mode™ CONTROL

TPS57140-Q1
www.ti.com
SLVSAP3A – DECEMBER 2010 – REVISED MARCH 2011
Co × Resr
C¦ =
Rc
(50)
For cases where the modulator zero is less than the cross over frequency (Aluminum or Tantalum capacitors),
the equations are:
R_C
=
V_OUT
G_MOD(fc) ´ f_Z(mod) ´ gm_(EA) ´ V_REF
(51)
Cc =
1
p × Rc × ¦p mod
(52)
1
C¦ =
2 ´ p ´ Rc ´ ¦z mod
(53)
For the example problem, the ESR zero is located at a higher frequency compared to the cross over frequency
so Equation 50 through Equation 53 are used to calculate the compensation components. For the example
problem, the components are calculated to be: Rc= 76.2kΩ, Cc= 2710pF, and Cf =6.17pF.
The calculated value of the Cf capacitor is not a standard value so a value of 2700pF will be used. 6.8pF is used
for Cc. Rc resistor sets the gain of the error amplifier which determines the cross over frequency. The calculated
Rc resistor is not a standard value, so 76.8kΩ will be used.
APPLICATION CURVES
VIN
VO
VOUT
IO
EN
IL
Figure 52. Load Transmit
VOUT
VIN
IL
Figure 53. Startup With EN
VOUT
IL
PH
Figure 54. VIN Power Up
Figure 55. Output Ripple CCM
Copyright © 2010–2011, Texas Instruments Incorporated
Product Folder Link(s): TPS57140-Q1
Submit Documentation Feedback
35