LTC3563 Ver la hoja de datos (PDF) - Linear Technology
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LTC3563 Datasheet PDF : 16 Pages
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LTC3563
APPLICATIO S I FOR ATIO
With this information we can calculate L using:
L
=
f
•
1
∆IL
•
VOUT
•
⎛
⎝⎜ 1–
VOUT
VIN
⎞
⎠⎟
Substituting VOUT = 1.87V, VIN = 4.2V, ΔIL = 200mA and
f = 2.25MHz gives:
L
=
1.87V
2.25MHz • 200mA
•
⎛
⎝⎜
1–
1.87V
4.2V
⎞
⎠⎟
=
2.31µH
With VOUT = 1.28V
L
=
1.28V
2.25MHz • 200mA
•
⎛
⎝⎜
1–
1.28V
4.2V
⎞
⎠⎟
= 1.98µH
Choosing a vendor’s closest inductor value of 2.2µH results
in a maximum ripple current of:
For VOUT = 1.87V
∆IL
=
1.87V
2.25MHz • 2.2µH
•
⎛⎝⎜1–
1.87V⎞
4.2V ⎠⎟
=
209.6mA
For VOUT = 1.28V
∆IL
=
1.28V
2.25MHz • 2.2µH
•
⎛⎝⎜1–
1.28V⎞
4.2V ⎠⎟
=
179.8mA
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.
Hot Swap is a trademark of Linear Technology Corporation.
VIN
2.7V TO 5.5V
L
VIN
SW
CIN
LTC3563
RUN
1.28V 1.87V
VSEL VOUT
GND
VOUT
COUT
3563 F03
Figure 3a. Typical Application
3563f
13
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