LTC3563 datasheet(13/16 Pages) LINER

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LTC3563

3563f

With this information we can calculate L using:

OUT

⎛

⎝⎜

⎞

⎠⎟

•

••

–

∆

Substituting VOUT = 1.87V, VIN = 4.2V, ΔIL = 200mA and

f = 2.25MHz gives:

MHz

⎛

⎝⎜

⎞

⎠⎟

187

2 25

200

187

231

.•

•–

. µ

µH

With V

MHz

OUT =

128

2 25

200

.•

•–

. 8

198

µH

⎛

⎝⎜

⎞

⎠⎟

Choosing a vendor’s closest inductor value of 2.2µH results

in a maximum ripple current of:

For V

MHz

µH

OUT

187

225

187

.• .

•–

∆

209 6

128

For V

OUT

⎛

⎝⎜

⎞

⎠⎟

∆

2 2

128

179 8

MHz

µH

•.

•–

⎛

⎝⎜

⎞

⎠⎟

APPLICATIO S I FOR ATIO

Hot Swap is a trademark of Linear Technology Corporation.

CIN will require an RMS current rating of at least

0.25A ≅ ILOAD(MAX)/2 at temperature and COUT will require

ESR of less than 0.2Ω. In most cases, ceramic capacitors

will satisfy these requirements. Select COUT = 10µF and

CIN = 10µF.

Figure 3 shows the complete circuit along with its efﬁciency

curve, load step response and recommended layout.

PC Board Layout Checklist

When laying out the printed circuit board, the following

checklist should be used to ensure proper operation of

the LTC3563. These items are also illustrated graphically

in Figure 3b. Check the following in your layout:

1. The power traces, consisting of the GND trace, the SW

trace and the VIN trace should be kept short, direct and

wide.

2. Does the (+) plate of CIN connect to VIN as closely as

possible? This capacitor provides the AC current to the

internal power MOSFETs.

3. Keep the (–) plates of CIN and COUT as close as possible.

Figure 3a. Typical Application

VIN

LTC3563

RUN

3563 F03

CIN

COUT

VIN

2.7V TO 5.5V

VOUT

VSEL

GND

1.28V 1.87V

LTC3563 Datasheet(PDF) 13 Page - Linear Technology

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