LTC3732CUHF View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTC3732CUHF
Linear Technology
LTC3732CUHF Datasheet PDF : 28 Pages
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LTC3732
APPLICATIO S I FOR ATIO
Total of all three main MOSFET’s AC loss:
PMAIN
≈
3(VIN)2
45A (2Ω)(1000pF)
(2)(3)
5V
1
– 1.8V
+
1
1.8V
(400kHz)
=
6.3W
This totals 1W at VIN = 8V, 2.25W at VIN = 12V and 6.25W
at VIN = 20V.
Total of all three synchronous MOSFET’s AC loss:
(3)Q
G
VIN
VDSSPEC
(f)
=
(6)(15nC
)
VIN
VDSSPEC
(4E5)
This totals 0.08W at VIN = 8V, 0.12W at VIN = 12V and
0.19W at VIN = 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)(4E5)
This totals 1.26W.
The total output power is (1.3V)(45A) = 58.5W and the
total input power is approximately 70W so the % loss of
each component is as follows:
Main switch AC loss (VIN = 12V) 2.25W 3.75%
Main switch DC loss
0.66W 1.1%
Synchronous switch AC loss 0.19W 0.3%
Synchronous switch DC loss 5.4W 9%
Power path loss
3.7W 6.1%
The numbers above represent the values at VIN = 12V. It
can be seen from this simple example that two things can
be done to improve efficiency: 1) Use two MOSFETs on the
synchronous side and 2) use a smaller MOSFET for the
main switch with smaller CMILLER 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.
PACKAGE DESCRIPTIO
G Package
36-Lead Plastic SSOP (5.3mm)
(Reference LTC DWG # 05-08-1640)
1.25 ±0.12
12.50 – 13.10*
(.492 – .516)
36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19
7.8 – 8.2
5.3 – 5.7
7.40 – 8.20
(.291 – .323)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2.
DIMENSIONS
ARE
IN
MILLIMETERS
(INCHES)
0.42 ±0.03
RECOMMENDED SOLDER PAD LAYOUT
3. DRAWING NOT TO SCALE
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED .152mm (.006") PER SIDE
5.00 – 5.60**
(.197 – .221)
**DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE
0.65 BSC
0° – 8°
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
2.0
(.079)
26
0.09 – 0.25
(.0035 – .010)
0.55 – 0.95
(.022 – .037)
0.65
(.0256)
BSC
0.22 – 0.38
(.009 – .015)
0.05
(.002)
G36 SSOP 0802
3732f
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