LM3677_0810 Datasheet, PDF(17/24 Page) National Semiconductor (TI) – 3MHz, 600mA Miniature Step-Down DC-DC Converter for Ultra Low Voltage Circuits

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LM3677_0810 Datasheet, PDF (17/24 Pages) National Semiconductor (TI) – 3MHz, 600mA Miniature Step-Down DC-DC Converter for Ultra Low Voltage Circuits

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TABLE 1. Suggested Inductors and Their Suppliers

Model

MIPSA2520D 1R0

LQM2HP 1R0

BRL2518T1R0M

Vendor

FDK

Murata

Taiyo Yuden

Dimensions LxWxH(mm)

2.5 x 2.0 x 1.2

2.5 x 2.0 x 0.95

2.5x 1.8 x 1.2

D.C.R (max)

100 mâ¦

80 mâ¦

OUTPUT CAPACITOR SELECTION

A ceramic output capacitor of 10 ÂµF, 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 char-

acteristics vary from manufacturer to manufacturer and dc

bias curves should be requested from them as part of the ca-

pacitor selection process.

The minimum output capacitance to guarantee good per-

formance is 5.75 ÂµF at 2.5V DC bias including tolerances

and over ambient temperature range. The output filter ca-

pacitor 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 dis-

charging of the output capacitor and by the RESR and can be

calculated as:

Voltage peak-to-peak ripple due to capacitance can be ex-

pressed as follows

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

follows

VPP-ESR = (2 * IRIPPLE) * RESR

Because these two components are out of phase the rms (root

mean squared) value can be used to get an approximate val-

ue of peak-to-peak ripple.

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

Note that the output voltage ripple is dependent on the induc-

tor current ripple and the equivalent series resistance of the

output capacitor (RESR).

The RESR is frequency dependent (as well as temperature

dependent); make sure the value used for calculations is at

the switching frequency of the part.

Model

4.7 ÂµF for CIN

C1608X5R0J475

C2012X5R0J475

GRM21BR60J475

JMK212BJ475

10 ÂµF for COUT

C1608X5R0J106

C2012X5R0J106

GRM21BR60J106

JMK212BJ106

TABLE 2. Suggested Capacitors and Their Suppliers

Type

Vendor

Voltage Rating

Ceramic, X5R

TDK

muRata

Taiyo-Yuden

TDK

muRata

Taiyo-Yuden

6.3V

Case Size

Inch (mm)

0603 (1608)

0805 (2012)

0603 (1608)

0805 (2012)

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