Datasheet

LTC3714
21
3714f
applicaTions inForMaTion
Figure 8. CPU Core Voltage Regulator 1.15V/15A at 300kHz without Active Voltage Positioning
C
C2
100pF
C
C1
2.2nF
C
SS
0.1µF
C
FB
100pF
C
ION
0.01µF
R
ON
330k
R
C
20k
3714 F08
R
PG
100k
R
F
1Ω
9
10
11
12
13
14
19
21
22
20
23
24
15
16
8
7
6
5
4
3
2
1
28
27
26
25
18
17
VID2
RUN/SS
V
ON
PGOOD
V
RNG
I
TH
SGND
I
ON
V
FB
FCB
V
OSENSE
VID3
OPV
IN
OP
–
VID1
VID0
BOOST
TG
SW
SENSE
PGND
BG
INTV
CC
V
IN
EXTV
CC
VID4
OPOUT
OP
+
C
B
0.33µF
M1
IRF7811
D1
UPS840
L1
0.68µH
M2
IRF7811
×2
D
B
CMDSH-3
C
VCC
4.7µF
C
F
0.1µF
5V
C
IN
22µF
25V
×3
V
IN
7V TO 24V
V
OUT
1.15V
15A
C
OUT
270µF
2V
×5
C
IN
: UNITED CHEMICON THCR70EIH226ZT
C
OUT
: PANASONIC EEFUE0D271
L1: SUMIDA CEP125-4712-T007
LTC3714
Next, choose the synchronous MOSFET switch. Because
of the narrow duty cycle and large current, a single SO-8
MOSFET will have difficulty dissipating the power lost in
the switch. Choosing two IRF7811s (R
DS(ON)
= 0.013Ω,
C
RSS
= 60pF) yields a nominal sense voltage of:
V
SNS(NOM)
= (15A)(0.5)(1.3)(0.013Ω) = 127mV
Tying V
RNG
to INTV
CC
will set the current sense voltage
range for a nominal value of 140mV with current limit
occurring at 186mV. To check if the current limit is ac-
ceptable, assume a junction temperature of about 100°C
above a 50°C ambient with ρ
150°C
= 1.6:
I
LIMIT
≥
186mV
0.5
( )
1.6
( )
0.013Ω
( )
+
1
2
5.4A
( )
= 20A
and double check the assumed T
J
in the MOSFET:
P
BOT
=
24V – 1.15V
24V
20A
2
⎛
⎝
⎜
⎞
⎠
⎟
2
1.6
( )
0.013Ω
( )
= 1.98W
T
J
= 50°C + (1.98W)(50°C/W) = 149°C