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| LTC3608 Datasheet, PDF (18/24 Pages) Linear Technology – 18V, 8A Monolithic Synchronous Step-Down DC/DC Converter | |||
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LTC3608
APPLICATIONS INFORMATION
PGND
INTVCC
CVCC
4.7μF
6.3V
SW
VIN
CF
RF1
0.47μF 1Ω
25V
40 39 38 37 36 35 34 33 32 31 30 29 28 27
EXTVCC
C4
0.01μF
SGND
VOUT
2.5V AT
8A
C5
22μF
6.3V
(OPTIONAL)
GND
COUT1 +
100μF
Ã2
L1
0.8μH
VIN
5V TO 18V
VIN
GND
CIN
C6 +
10μF
10μF
35V
35V
3Ã
(OPTIONAL)
41 SW
42 SW
43 SW
44 SW
45
SW
46 SW
47 SW
48 PVIN
49 PVIN
50 PVIN
51
PVIN
52
PVIN
LTC3608
SGND 26
NC 25
NC 24
VFB 23
ION 22
NC 21
SGND 20
FCB 19
ITH 18
VRNG 17
16
PGOOD
SGND 15
(OPTIONAL)
R1
R2
9.5k
C1
30.1k
C2
1%
1%
(OPTIONAL) RON
187k
VOUT
1%
VIN
CON
0.01μF
(OPTIONAL)
R5
11.3k
CC1
1500pF
R3
0Ω
RPG1
100k
C3
CC2
100pF
1 2 3 4 5 6 7 8 9 10 11 12 13 14
CIN: TAIYO YUDEN GMK325BJ106MM-B
COUT: TDKC2012X5ROJ226M
L1: CDEP85NP-R80MC-50
C5: MURATA GRM31CR60J226KE19
KEEP POWER GROUND AND SIGNAL GROUND SEPARATE.
CONNECT AT ONE POINT.
= PGND
SW
INTVCC
DB
CMDSH-3
CB1
0.22μF
SW
CSS
0.1μF
RSS1
510k
VIN
(OPTIONAL)
INTVCC (OPTIONAL)
RVON
0Ω
0.1μF
SGND
VOUT
3608 F06
= SGND
Figure 6. Design Example: 5V to 18V Input to 2.5V/8A at 550kHz
⢠Use a compact plane for the switch node (SW) to improve
cooling of the MOSFETs and to keep EMI down.
⢠Use planes for VIN and VOUT to maintain good voltage
ï¬ltering and to keep power losses low.
⢠Flood all unused areas on all layers with copper. Flood-
ing with copper reduces the temperature rise of power
components. Connect these copper areas to any DC
net (VIN, VOUT, GND or to any other DC rail in your
system).
When laying out a printed circuit board without a ground
plane, use the following checklist to ensure proper opera-
tion of the controller. These items are also illustrated in
Figure 7.
⢠Segregate the signal and power grounds. All small
signal components should return to the SGND pin at
one point, which is then tied to the PGND pin.
⢠Connect the input capacitor(s) CIN close to the IC. This
capacitor carries the MOSFET AC current.
⢠Keep the high dV/dT SW, BOOST and TG nodes away
from sensitive small-signal nodes.
⢠Connect the INTVCC decoupling capacitor CVCC closely
to the INTVCC and PGND pins.
⢠Connect the top driver boost capacitor CB closely to
the BOOST and SW pins.
⢠Connect the VIN pin decoupling capacitor CF closely to
the VIN and PGND pins.
3608fa
18
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