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参数资料
| 型号： | AN-53 |
| 厂商： | Fairchild Semiconductor Corporation |
| 元件分类： | DC/DC变换器 |
| 英文描述： | Implementing an RC5051 DC-DC Converter on Pentium II Motherboards |
| 中文描述： | 推行RC5051的DC - DC转换器的奔腾II主板 |
| 文件页数： | 9/20页 |
| 文件大小： | 143K |
| 代理商： | AN-53 |
APPLICATION NOTE
AN53
9
Converter Efficiency
Losses due to parasitic resistance in the switches, coil, and
sense resistor dominate at high load-current level. The major
loss mechanisms under heavy loads, in typical order of
importance, are:
MOSFET I
2
R losses
Transition losses
Formulae for Calculation of Converter Efficiency
Sense Resistor losses
Input Capacitor losses
Coil Losses
Losses due to the operating supply current of the IC.
Diode-conduction losses
Gate-charge losses
, with T
DT
the deadtime
Example Efficiency Calculation
As an example, the efficiency of a synchronous 14A converter based on the RC5051 will be calculated. The converter produces
2.8V output from a 5V input, switches at 300kHz, has MOSFETs with a 4nF gate capacitance, RDS,on = 10m
W
for both MOS-
FETS and a rise and fall time of 50nsec. The inductor has a winding resistance of 3m
W,
and the sense resistor used is 5.2m
W
. The
schottky paralleled with the synchronous rectifier has a forward voltage of 400mV at 14A. The input capacitors have a total ESR
of 15m
W
.
Efficiency
P
p
IN
+
-------------
V
I
V
OUT
I
OUT
P
RISE
P
FALL
+
P
LOSS
P
INDUCTOR
+
-------------------------------------------------
=
=
P
LOSS
P
RDS
(
)
P
SENSE
P
GATE
P
DIODE
P
CAPS
P
IC
+
+
+
+
+
+
=
P
RDS
I
OUT
2
R
DS,ON
DC
=
for the high-side MOSFET
P
RDS
I
OUT
2
R
DS,ON
1
DC
–
(
)
=
for the low-side MOSFET
V
I
t
F
S
V
I
t
F
S
2
R
INDUCTOR
P
RISE
P
FALL
+
------------------2
V
I
t
F
V
I
t
F
-------------------2
+
=
P
RISE
P
FALL
+
------------------2
-------------------2
+
=
P
INDUCTOR
I
OUT
=
P
SENSE
I
OUT
CV
2
F
S
for each MOSFET
2
R
SENSE
=
P
GATE
=
P
DIODE
I
OUT
V
F
T
DT
F
S
=
P
CAPS
ESR
I
OUT
2
DC
′
1
DC
–
(
)
′
′
=
P
IC
25mA
*
V
CC
=
P
RDS
14A
(
)
2
10m
W
1.96W
=
=
P
RISE
P
FALL
+
5V
14A 50nsec
50nsec
+
)
300kHz
′
2
1.05W
=
=
P
RISE
P
FALL
+
400mV
14A 50nsec
50nsec
+
)
300kHz
′
2
84mW
=
=
P
INDUCTOR
14A
(
)
2
3m
W
590mW
=
=
P
SENSE
14A
(
)
2
5.2m
W
1.02W
=
=
P
GATE
P
DIODE
4nF 5V
)
2
300kHz
2
′
60mW
=
=
14A
400mV
′
50nsec
′
300kHz
′
84mW
=
=
P
CAPS
15m
W
14A
(
)
2
′
0.56
′
1
0.56
–
(
)
′
724mW
=
=
P
IC
25mA
5V
′
125mW
′
=
P
LOSS
1.96W
1.05W
0.084W
0.59W
1.02W
0.06W
0.084W
0.724W
0.125W
+
+
+
+
+
+
+
+
5.70W
=
=
Efficiency
′
14A
+
′
2.8V
14A
5.70W
----------2.8V
87%
=
=
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