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ADP1621ARMZ-R7 データシート(PDF) 21 Page - Analog Devices

部品番号 ADP1621ARMZ-R7
部品情報  Constant-Frequency, Current-Mode Step-Up DC-to-DC Controller
PDF  32 Pages
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メーカー  AD [Analog Devices]
ホームページ  http://www.analog.com
Logo AD - Analog Devices

ADP1621ARMZ-R7 データシート(HTML) 21 Page - Analog Devices

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Data Sheet
ADP1621
Rev. D | Page 21 of 32
EFFICIENCY CONSIDERATIONS
The efficiency, η, of a dc-to-dc converter is given by
%
100
×
=
IN
OUT
P
P
η
(38)
where:
POUT is the output power.
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.
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.
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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