V

PP-RMS

=

V

PP-C

PP-ESR

2

4*f*C

r =

r

2

12

1 -

+

¸¸

¹

·

¨¨

©

§

x

x

L

f

x

x

x

LM8801

www.ti.com

SNVS597H – APRIL 2009 – REVISED MAY 2013

(2)

Table 1. Suggested Inductors and Suppliers

Model

Vendor

Dimensions LxWxH (mm)

MIPSZ2012D0R5

FDK

2.0 x 1.2 x 1.0

LQM21PNR54MG0D

Murata

2.0 x 1.2 x 0.9

HSLI-201208AG-R47

Hitachi Metals

2.0 x 1.2 x 0.8

OUTPUT CAPACITOR SELECTION

Use a 4.7

μF, 6.3V ceramic capacitor, X7R or X5R types; do not use Y5V. DC bias characteristics of ceramic

capacitors must be considered when selecting case sizes 0402 and 0603. DC bias characteristics vary from

manufacturer to manufacturer, and DC bias curves should be requested from them as part of the capacitor

selection process. Minimum output capacitance to ensure good performance is 2.2 µF (for 4.7 µF

capacitor) at 1.8V DC bias including tolerances and over ambient temp range.

The output filter capacitor smooths out current flow from the inductor to the load, helps maintain a steady output

voltage during transient load changes and reduces output voltage ripple. These capacitors must be selected with

sufficient capacitance and sufficiently low ESR to perform these functions.

The output voltage ripple is caused by the charging and discharging of the output capacitor and also due to its

Voltage peak-to-peak ripple due to capacitance =

(3)

Voltage peak-to-peak ripple due to ESR =

Because these two components are out of phase, the rms value can be used to get an approximate value of

peak-to-peak ripple.

Voltage peak-to-peak ripple, root mean squared =

(4)

Note that the output voltage ripple is dependent on the current ripple and the equivalent series resistance of the

value used for calculations is at the switching frequency of the part.

Table 2 lists suggested capacitors and suppliers.

Table 2. Suggested Capacitors and Suppliers

Case Size

Model

Vendor

Inch (mm)

Murata

0402 (1005)

Taiyo Yuden

0402 (1005)

Samsung

0402 (1005)

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