LTC3730_15 Datasheet, PDF (26/28 Pages) Linear Technology – 3-Phase, 5-Bit Intel Mobile VID, 600kHz, Synchronous Buck Controller

LTC3730
APPLICATIO S I FOR ATIO
Total of all three synchronous MOSFETs’ AC gate loss:
(3)Q_G
V_IN
V_DSSPEC
(f)
=
(6)(15nC)
V_IN
V_DSSPEC
(4E5)
This totals 0.08W at V_CC = 8V, 0.12W at V_CC = 12V and
0.19W at V_CC = 20V. The bottom MOSFET does not
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:
2 • 3(0.7V)(15A)(50ns)(41E5)
This totals 1.26W.
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:
Main switches’ AC loss (V_IN = 12V) 2.25W 3.75%
Main switches’ DC loss
0.87W 1.5%
Synchronous switches’ AC loss 0.19W 0.3%
Synchronous switches’ DC loss 7.2W 12%
Power path loss
3.375W 5.6%
The numbers above represent the values at V_IN = 12V. This
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_MILLER to better balance the AC loss
with the DC loss. A smaller, less expensive MOSFET can
actually perform better in the task of the main switch.
TYPICAL APPLICATIO
OPTIONAL FOR
SYNCHRONIZATION
1000pF 5V
30k
10k
1
VID1 IN
2
3
4
5
100pF
6
27pF
7
8
9
S1⁺
10
S1^{– 1000pF}
11
S2⁺
12
S2^{– 1000pF}
13
S3^–
14
0.01µF S3^{+ 1000pF}
15
16
I_TH 17
470pF
1.5nF
5.1k
18
VID2 IN
VID1
VID0
PLLIN PGOOD
PLLFLTR BOOST1
FCB
TG1
IN⁺
LTC3730
SW1
IN^–
BOOST2
AMPOUT
TG2
EAIN
SW2
SGND
SENSE1⁺
SENSE1^–
SENSE2⁺
SENSE2^–
SENSE3^–
SENSE3⁺
V_CC
BG1
PGND
BG2
BG3
SW3
TG3
RUN/SS BOOST3
I_TH
VID4
VID2
VID3
36
5V _PGOOD
VID0 IN
35
34
33
0.1µF ^1Ω
32
31
30
0.1µF
29
28
5V
27
26
1µF
10µF
25
24
23
22
21
0.1µF
20
VID3 IN
19
VID4 IN _5V
47k
5V
V_IN
M1
L1
0.003Ω
M2
D1
S1⁺
S1^–
V_IN
M3
L2
0.003Ω
M4
D2
S2⁺
S2^–
V_IN
M5
L3
0.003Ω
M6
D3
S3⁺
S3^–
3730 TA01
V_OUT
10µF +
6.3V
×3
C_OUT
10µF +
35V
×4
V_IN
C_IN ^{5V TO 24V}
68µF
25V
V_OUT: 0.6V TO 1.75V, 45A
SWITCHING FREQUENCY: 300kHz
C_IN: SANYO OS-CON 25SP68M
C_OUT: 270µF/2V ×6 PANASONIC SP EEUE0D271R
D1 TO D3: B140A DIODES INC
L1 TO L3: SUMIDA 1µH/20A CEP125 IROMC-H
OR 1µH/19A PANASONIC PCC-D126H
OR TOKO EH125C
M1, M3, M5: IRF7811W OR FDS6688 OR Si7860DP OR HAT2168H
M2, M4, M6: Si7856DP OR HAT2165H
Figure 14. CPU Application 0.6V to 1.75V, 45A Power Supply
3730fa
26