LTC3854 LINER [Linear Technology], LTC3854 Datasheet - Page 22

• Manufacturer Part Number: LTC3854
• Description: Small Footprint, Wide VIN Range Synchronous Step-Down DC/DC Controller
• Manufacturer: LINER [Linear Technology]

LTC3854
applicaTions inForMaTion
Choosing an RJK0330DPB for the bottom FET will pro-
vide:
BV
R
Q
Assuming a thermal resistance of 40°C/W for the main and
synchronous FETs, the resulting junction temperatures at
an ambient of 60°C will be 82°C and 104°C, respectively.

DS(ON)
G
DSS
P
P
= 27nC, typical, at V
SYNC
SYNC
= 30V
= 3.9mΩ maximum at 25°C, V
=
= 1.1W
• 1+ 0.005 • 100°C – 25°C
20V − 1.2V
(
20V
0.1µF
GS
• 15A
(
D1 = CMDSH-3
M1 = RENESAS RJK0305DPB
M2 = RENESAS RJK0330DPB
L = VISHAY IHLP4040DZ-01 0.56µH
C
C
(
OUT1
OUT2
3.9k
10k
4.99k
= 4.5V
2200pF
= SANYO 2R5TPE330M9
= MURATA GRM31CR60J476K
)
2
100pF
Figure 6. 1.2V/15A Converter from Design Example
GS
)
)
RUN/SS
ITH
FB
SENSE
SENSE
• 3.9mΩ
= 4.5V
LTC3854
–
+
BOOST
INTV
GND
SW
V
BG
TG
CC
IN
D1
4.7µF
0.1µF
Some airflow may be required for higher ambient tem-
peratures. A maximum MOSFET junction temperature of
110°C at worst case ambient generally provides adequate
margin.
Given a typical Q
for the RJK0330DPB and the 400kHz switching frequency,
the current supplied by INTV
The resulting controller temperature at 60°C and a 20V
input will be:
which is well under the maximum junction temperature
of 125°C.
I
T
GATECHG
J
M1
M2
= 60°C + 20V • 14mA • 76°C/W = 81°C
1.8m DCR
3.09k
0.56µH
L
= (8nC + 27nC) • 400kHz = 14mA
0.1µF
180µF
25V
G
3854 F06
of 8nC for the RJK0305DPB and 27nC
10µF
25V
2
C
47µF
+
OUT2
CC
C
330µF
V
4.5V TO 28V
V
1.2V
15A
OUT1
2
IN
OUT
will be:
3854fa