ltc3730 Linear Technology Corporation, ltc3730 Datasheet - Page 26

• Manufacturer Part Number: ltc3730
• Description: 3-phase, 5-bit Intel Mobile Vid, 600khz, Synchronous Buck Controller
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LTC3730
Total of all three synchronous MOSFETs’ AC gate loss:
This totals 0.08W at V
0.19W at V
experience the Miller capacitance dissipation issue that
the main switch does because the bottom switch turns on
when its drain is close to ground
The Schottky rectifier loss assuming 50ns nonoverlap
time:
This totals 1.26W.
TYPICAL APPLICATIO
26
SYNCHRONIZATION
2 • 3(0.7V)(15A)(50ns)(41E5)
( )
OPTIONAL FOR
3
V
SWITCHING FREQUENCY: 300kHz
C
C
Q
1000pF
OUT
IN
OUT
100pF
470pF
5.1k
10k
G
: SANYO OS-CON 25SP68M
: 0.6V TO 1.75V, 45A
: 270µF/2V ×6 PANASONIC SP EEUE0D271R
V
0.01µF
DSSPEC
1.5nF
V
CC
IN
5V
30k
= 20V. The bottom MOSFET does not
27pF
S1
S1
S2
S2
S3
S3
( ) ( )(
+
–
+
–
–
+
U
f
1000pF
1000pF
1000pF
=
CC
VID1 IN
VID2 IN
6 15
U
= 8V, 0.12W at V
I
TH
nC
10
11
12
13
14
15
16
17
18
1
2
3
4
5
6
7
8
9
Figure 14. CPU Application 0.6V to 1.75V, 45A Power Supply
)
VID1
PLLIN
PLLFLTR
FCB
IN
IN
AMPOUT
EAIN
SGND
SENSE1
SENSE1
SENSE2
SENSE2
SENSE3
SENSE3
RUN/SS
I
VID2
TH
V
U
+
–
W
DSSPEC
V
LTC3730
IN
+
–
+
–
–
+
BOOST1
BOOST2
BOOST3
D1 TO D3: B140A DIODES INC
L1 TO L3: SUMIDA 1µH/20A CEP125 IROMC-H
PGOOD
PGND
VID0
VID4
VID3
(
SW1
SW2
SW3
BG1
BG2
BG3
TG1
TG2
TG3
V
4 5
CC
CC
E
= 12V and
U
)
OR 1µH/19A PANASONIC PCC-D126H
OR TOKO EH125C
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
VID0 IN
VID3 IN
VID4 IN
1µF
0.1µF
5V
0.1µF
0.1µF
5V
PGOOD
The total output power is (1.3V)(45A) = 58.5W and the
total input power is approximately 60W so the % loss of
each component is as follows:
The numbers above represent the values at V
simple example shows that two things can be done to
improve efficiency: 1) Use two MOSFETs on the synchro-
nous side and 2) use a smaller MOSFET for the main
switch with smaller C
with the DC loss. A smaller, less expensive MOSFET can
actually perform better in the task of the main switch.
10µF
5V
Main switches’ AC loss (V
Main switches’ DC loss
Synchronous switches’ AC loss
Synchronous switches’ DC loss
Power path loss
1Ω
47k
M1
M2
M3
M4
M5
M6
3730 TA01
M1, M3, M5: IRF7811W OR FDS6688 OR Si7860DP OR HAT2168H
M2, M4, M6: Si7856DP OR HAT2165H
5V
V
V
V
IN
IN
IN
D1
D2
D3
L1
L2
L3
MILLER
S1
S2
S3
+
+
+
0.003Ω
0.003Ω
0.003Ω
to better balance the AC loss
S1
S2
S3
IN
–
–
–
= 12V) 2.25W 3.75%
10µF
6.3V
×3
10µF
35V
×4
0.87W 1.5%
0.19W 0.3%
7.2W
3.375W 5.6%
+
+
V
OUT
IN
C
C
68µF
25V
= 12V. This
OUT
IN
V
5V TO 24V
12%
IN
3730fa