Datasheet

F =
LC
1
2 Lp
O O
xC (EFF)Ö
Fp1=500000x
V
O
F
LC
Fz1=0.7xF
LC
Fz2=2.5xF
LC
C7=
1
2 xFp1x(R1||R2)p
R3=
1
2 xFz1xC7p
C6=
1
2 xFz2xR1p
TPS5410-Q1
www.ti.com ......................................................................................................................................................................................... SLVSA23 –SEPTEMBER 2009
External Compensation Network
When using ceramic output capacitors, additional circuitry is required to stabilize the closed loop system. For this
circuit the external components are R3, C5, C6 and C7. To determine the value of these components, first
calculate the LC resonant frequency of the output filter:
(14)
For this example the effective resonant frequency is calculated as 2306 Hz
The network composed of R1, R2, R3, C5, C6 and C7 has two poles and two zeros that are used to tailor the
overall response of the feedback network to accommodate the use of the ceramic output capacitors. The pole
and zero locations are given by the following equations:
(15)
(16)
(17)
The final pole is located at a frequency too high to be of concern. The values for R1 and R2 are fixed by the 5-V
output voltage as calculated using Equation 12. Now the values of R3, C5, C6 and C7 are determined using
Equation 18, Equation 19, and Equation 20:
(18)
(19)
(20)
For this design, using the closest standard values, C7 is 0.056 μF, R3 is 1.76 kΩ and C6 is 2700 pF. C5 is
added to improve load regulation performance. It is effectively in parallel with C6 in the location of the second
pole frequency, so it should be small in relationship to C6. C5 should be less the 1/10 the value of C6. For this
example, 150 pF works well.
For additional information on external compensation of the TPS5410 or other wide voltage range SWIFT devices,
see SLVA237 Using TPS5410/20/30/31 With Aluminum/Ceramic Output Capacitors.
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