Datasheet

C6=

2 xFz2xR1p

R3=

2 xFz1xC7p

C7=

2 xFp1x(R1||R2)p

Fz2=2.5xF

Fz1=0.7xF

Fp1=500000x

F =

2 Lp

O O

xC (EFF)Ö

TPS5410

www.ti.com

SLVS675C –AUGUST 2006–REVISED SEPTEMBER 2013

The minimum capacitor value is calculated to be 7.6 μF. For this circuit a larger value of capacitor will yield better

transient response. Two output capacitors are used for C3 and C4 with a value of 47 uF each. It is important to

note that the actual capacitance of ceramic capacitors decreases with applied voltage. In this case the effective

value used for the calculations is approximately 70 % of the rated value or 70 μF.

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 devices, see

SLVA237 Using TPS5410/20/30/31 With Aluminum/Ceramic Output Capacitors.

Product Folder Links: TPS5410