LTC3418 データシートの表示（PDF） - Linear Technology
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LTC3418 Datasheet PDF : 20 Pages
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LTC3418
APPLICATIONS INFORMATION
Because efficiency is important at both high and low load
current, Burst Mode operation will be utilized.
First, calculate the timing resistor:
ROSC
=
7.3 • 1010
1• 106
– 2.5k
= 70.5k
Use a standard value of 69.8k. Next, calculate the inductor
value for about 40% ripple current:
L
=
2.5V
(1MHz) (3.2A )
1–
2.5V
3.3V
=
0.19μH
Using a 0.2μH inductor results in a maximum ripple cur-
rent of:
IL
=
2.5V
(1MHz) (0.2μH)
1–
2.5V
3.3V
=
3.03A
COUT will be selected based on the ESR that is required to
satisfy the output voltage ripple requirement and the bulk
capacitance needed for loop stability. For this design, five
100μF ceramic capacitors will be used.
CIN should be sized for a maximum current rating of:
IRMS
=
(8A)
2.5V
3.3V
3.3V
2.5V
–
1=
3.43ARMS
Decoupling the PVIN and SVIN pins with four 100μF capaci-
tors is adequate for this application.
The burst clamp and output voltage can now be pro-
grammed by choosing the values of R1, R2 and R3. The
voltage on the MODE pin will be set to 0.67V by the resistor
divider consisting of R2 and R3. A burst clamp voltage of
0.67V will set the minimum inductor current, IBURST, to
approximately 1.2A.
14
VIN
3.3V
CSVIN
1μF
X7R
CIN
100μF
×4
RSVIN
100Ω
RSS RPG
2.2M 100k
3
PVIN
4
PVIN
9
PVIN
10
PVIN
22
PVIN
23
PVIN
28
PVIN
29
PVIN
24
SVIN
1
SW
2
SW
11
SW
12
SW
20
SW
21
SW
30
SW
31
SW
25
VFB
CSS
1000pF
X7R
CITH
820pF
X7R
RITH
7.5k
C1
47pF
X7R
LTC3418
35
27
TRACK SYNC/MODE
5
PGOOD
38
PGND
7
RUN/SS
37
PGND
26
ROSC 69.8k 6
8
ITH
RT
SGND
36
PGND
34
PGND
33
PGND
13
PGND
32
PGND
14
PGND
19
PGND
15
PGND
18
PGND
17
PGND
16
VREF
CIN, COUT: AVX 18126D107MAT
L1: TOKO FDV0620-R20M
L1
0.2μH
C1
22pF
X7R
R1
432k
COUT
100μF
×5
VOUT
2.5V
8A
R2
33.2k
R3
169k
CREF
2.2μF
X7R
3418 F04
VREF
Figure 4. 2.5V, 8A Regulator at 1MHz, Burst Mode Operation
3418fb
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