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LTM4607 数据表(PDF) 23 Page - Linear Technology

部件名 LTM4607
功能描述  High Effi ciency, Synchronous, 4-Switch Buck-Boost Controller
PDF  28 Pages
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制造商  LINER [Linear Technology]
网页  http://www.linear.com
标志 LINER - Linear Technology

LTM4607 数据表(HTML) 23 Page - Linear Technology

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LTC3780
23
3780fe
APPLICATIONS INFORMATION
Double-check the TJ in the MOSFET with 70°C ambient
temperature:
TJ = 70°C + 1.94W • 40°C/W = 147.6°C
The maximum power dissipation of switch B occurs in
buck mode. Assuming a junction temperature of TJ = 80°C
with
ρ80°C = 1.2, the power dissipation at VIN = 18V is:
PB,BUCK =
18 – 12
18
•5
2 •1.2•0.009 = 90mW
Double-check the TJ in the MOSFET at 70°C ambient
temperature:
TJ = 70°C + 0.09W • 40°C/W = 73.6°C
The maximum power dissipation of switch C occurs in boost
mode. Assuming a junction temperature of TJ = 110°C with
ρ110°C = 1.4, the power dissipation at VIN = 5V is:
PC,BOOST =
12 – 5
(
)•12
5
2
•5
2 •1.4•0.009
+ 2•12
3 •
5
5
•150p • 400k
= 1.27W
Double-check the TJ in the MOSFET at 70°C ambient
temperature:
TJ = 70°C + 1.08W • 40°C/W = 113°C
The maximum power dissipation of switch D occurs
in boost mode when its duty cycle is higher than 50%.
Assuming a junction temperature of TJ = 100°C with
ρ100°C = 1.35, the power dissipation at VIN = 5V is:
PW
D BOOST
,
=
⎛
⎝⎜
⎞
⎠⎟
=
5
12
12
5
5
1 35 0 009 0 73
2
Double-check the TJ in the MOSFET at 70°C ambient
temperature:
TJ = 70°C + 0.73W • 40°C/W = 99°C
CIN is chosen to filter the square current in buck mode. In
this mode, the maximum input current peak is:
IA
IN PEAK MAX BUCK
,(
,
)
%
.
=+
⎛
⎝⎜
⎞
⎠⎟
=
51
29
2
57
A low ESR (10mΩ) capacitor is selected. Input voltage
ripple is 57mV (assuming ESR dominate ripple).
COUT is chosen to filter the square current in boost mode.
In this mode, the maximum output current peak is:
IOUT PEAK MAX BOOST
,(
,
)
%
.
=+
⎛
⎝⎜
⎞
⎠⎟
=
12
5
51
11
2
10 6
6A
A low ESR (5mΩ) capacitor is suggested. This capacitor
will limit output voltage ripple to 53mV (assuming ESR
dominate ripple).
PC Board Layout Checklist
The basic PC board layout requires a dedicated ground
plane layer. Also, for high current, a multilayer board
provides heat sinking for power components.
• The ground plane layer should not have any traces and
it should be as close as possible to the layer with power
MOSFETs.
• Place CIN, switch A, switch B and D1 in one com-
pact area. Place COUT, switch C, switch D and D2 in
one compact area. One layout example is shown in
Figure 10.
GND
VOUT
COUT
L
RSENSE
3780 F10
QD
QC
QB
QA
SW2
SW1
D1
D2
VIN
CIN
LTC3780
CKT
Figure 10. Switches Layout



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