V

PP-RMS

=

V

PP-C

PP-ESR

2

4*f*C

LM3677

www.ti.com

SNVS502E – MARCH 2007 – REVISED OCTOBER 2008

Table 2. Suggested Inductors and Their Suppliers

Model

Vendor

Dimensions LxWxH(mm)

D.C.R (max)

MIPSA2520D 1R0

FDK

2.5 x 2.0 x 1.2

100 m

Ω

LQM2HP 1R0

Murata

2.5 x 2.0 x 0.95

100 m

Ω

BRL2518T1R0M

Taiyo Yuden

2.5x 1.8 x 1.2

80 m

Ω

OUTPUT CAPACITOR SELECTION

A ceramic output capacitor of 10 µF, 6.3V is sufficient for most applications. Use X7R or X5R types; do not use

Y5V. DC bias characteristics of ceramic capacitors must be considered when selecting case sizes like 0603 and

0805. DC bias characteristics vary from manufacturer to manufacturer and dc bias curves should be requested

from them as part of the capacitor selection process.

The minimum output capacitance to guarantee good performance is 5.75 µF at 2.5V DC bias including

tolerances and over ambient temperature 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.

can be calculated as:

Voltage peak-to-peak ripple due to capacitance can be expressed as follows

(3)

Voltage peak-to-peak ripple due to ESR can be expressed as follows

Because these two components are out of phase the rms (root mean squared) value can be used to get an

approximate value of peak-to-peak ripple.

Voltage peak-to-peak ripple, rms can be expressed as follow:

(4)

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

is at the switching frequency of the part.

Table 3. Suggested Capacitors and Their Suppliers

Case Size

Model

Type

Vendor

Voltage Rating

Inch (mm)

C1608X5R0J475

Ceramic, X5R

TDK

6.3V

0603 (1608)

C2012X5R0J475

Ceramic, X5R

TDK

6.3V

0805 (2012)

GRM21BR60J475

Ceramic, X5R

muRata

6.3V

0805 (2012)

JMK212BJ475

Ceramic, X5R

Taiyo-Yuden

6.3V

0805 (2012)

C1608X5R0J106

Ceramic, X5R

TDK

6.3V

0603 (1608)

C2012X5R0J106

Ceramic, X5R

TDK

6.3V

0805 (2012)

GRM21BR60J106

Ceramic, X5R

muRata

6.3V

0805 (2012)

JMK212BJ106

Ceramic, X5R

Taiyo-Yuden

6.3V

0805 (2012)

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