IN

OUT

OUT

=

Co(RMS)

IN

O

SW

V

x (V

- V

)

12 x V

x L

x

I

f

2

2

=

IPP

Lo(RMS)

O

1

+

12

I

I

I

lpp

=

+

Ipeak

O

2

I

I

I

V

V

V

IN(max)

OUT

OUT

=

x

IPP

V

L

x

IN(max)

O

SW

-

I

f

TPS54528

www.ti.com

SLVSAY4B – JULY 2011 – REVISED MAY 2012

Table 1. Recommended Component Values

Output Voltage (V)

R1 (k

Ω)

R2 (k

Ω)

L1 (µH)

C8 + C9 (µF)

1

6.81

22.1

1.0 - 1.5

22 - 68

1.05

8.25

22.1

1.0 - 1.5

22 - 68

1.2

12.7

22.1

1.0 - 1.5

22 - 68

1.5

21.5

22.1

1.5

22 - 68

1.8

30.1

22.1

5 - 22

1.5

22 - 68

2.5

49.9

22.1

5 - 22

2.2

22 - 68

3.3

73.2

22.1

5 - 22

2.2

22 - 68

5

124

22.1

5 - 22

3.3

22 - 68

(1)

Optional

Since the DC gain is dependent on the output voltage, the required inductor value increases as the output

voltage increases. For higher output voltages at or above 1.8 V, additional phase boost can be achieved by

adding a feed forward capacitor (C4) in parallel with R1

The inductor peak-to-peak ripple current, peak current and RMS current are calculated using Equation 5,

Equation 6 and Equation 7. The inductor saturation current rating must be greater than the calculated peak

current and the RMS or heating current rating must be greater than the calculated RMS current. Use 700 kHz for

current of Equation 7.

(5)

(6)

(7)

For this design example, the calculated peak current is 5.51 A and the calculated RMS current is 5.01 A. The

inductor used is a TDK SPM6530-1R5M100 with a peak current rating of 11.5 A and an RMS current rating of 11

A.

The capacitor value and ESR determines the amount of output voltage ripple. The TPS54528 is intended for use

with ceramic or other low ESR capacitors. Recommended values range from 22µF to 68µF. Use Equation 8 to

determine the required RMS current rating for the output capacitor.

(8)

For this design two TDK C3216X5R0J226M 22µF output capacitors are used. The typical ESR is 2 m

Ω each.

The calculated RMS current is 0.29 A and each output capacitor is rated for 4A.

Input Capacitor Selection

The TPS54528 requires an input decoupling capacitor and a bulk capacitor is needed depending on the

application. A ceramic capacitor over 10

μF is recommended for the decoupling capacitor. An additional 0.1 µF

capacitor (C3) from pin 8 to ground is optional to provide additional high frequency filtering. The capacitor voltage

rating needs to be greater than the maximum input voltage.

Bootstrap Capacitor Selection

A 0.1 µF. ceramic capacitor must be connected between the VBST to SW pin for proper operation. It is

recommended to use a ceramic capacitor.

Copyright © 2011–2012, Texas Instruments Incorporated

13

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