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ADP1621ARMZ-R7 数据表(PDF) 21 Page - Analog Devices

部件名 ADP1621ARMZ-R7
功能描述  Constant-Frequency, Current-Mode Step-Up DC/DC Controller
PDF  32 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
制造商  AD [Analog Devices]
网页  http://www.analog.com
标志 AD - Analog Devices

ADP1621ARMZ-R7 数据表(HTML) 21 Page - Analog Devices

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ADP1621
Rev. A | Page 21 of 32
EFFICIENCY CONSIDERATIONS
The efficiency, η, of a dc/dc converter is given by
%
100
×
=
IN
OUT
P
P
η
(38)
where POUT is the output power, and PIN is the input power to the
converter. While switching regulators are ideally lossless converters
of power, the nonideal characteristics of regulator components
degrade the efficiency of the regulator.
The primary sources of power dissipation in the regulator include
•
The power dissipation in the external power MOSFET due
to conduction and switching losses.
SW
C
MOSFET
P
P
P
+
=
(39)
+
⎥
⎦
⎤
⎢
⎣
⎡
+
×
×
×
⎟
⎠
⎞
⎜
⎝
⎛
−
=
)
1
(
1
K
R
D
D
I
DSON
LOAD
⎥
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎢
⎣
⎡
×
+
×
−
×
+
2
)
(
1
)
(
SW
F
R
LOAD
D
OUT
f
t
t
D
I
V
V
•
The power dissipation in the external current-sense
resistor if lossless current sensing is not used.
CS
LOAD
CS
R
D
D
I
P
×
×
⎟
⎠
⎞
⎜
⎝
⎛
−
=
2
1
(40)
•
The power dissipation in the external diode.
LOAD
D
DIODE
I
V
P
×
=
(41)
•
The power dissipation in the winding resistance of the
power stage inductor.
W
LOAD
W
L
R
D
I
P
×
⎟
⎠
⎞
⎜
⎝
⎛
−
=
2
,
1
(42)
•
The supply current to the ADP1621 IC, which includes the
quiescent current and the gate driver charging current. The
power dissipation due to gate charging loss is approximated by
SW
G
PIN
G
f
Q
V
P
×
×
=
(43)
where PG is the gate charging power loss, VPIN is the voltage at
the PIN pin, QG is the MOSFET total gate charge, and fSW is
the converter switching frequency. Therefore, the total power
dissipation in the IC itself is given by
(
)
Q
IN
G
IC
I
V
P
P
×
+
=
(44)
(
)
(
)
Q
IN
SW
G
PIN
I
V
f
Q
V
×
+
×
×
=
where PIC is the total power dissipated in the IC, IQ is the
quiescent current, and VIN is the voltage at the IN pin.
The secondary sources of power dissipation in the regulator include
•
The power dissipation in the ESR of the input and output
capacitors.
•
Inductor core losses due to hysteresis and eddy currents.



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