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ADP2102
SETTING THE OUTPUT VOLTAGE
Table 7. ADP2102-ADJ Configurations for V OUT
The output voltage of the ADP2102-ADJ is externally set by
a resistive voltage divider from the output voltage to FB. The ratio
of the resistive voltage divider sets the output voltage, and the
absolute value of those resistors sets the divider string current. For
lower divider string currents, the small 10 nA (50 nA maximum)
FB bias current should be taken into account when calculating
resistor values. The FB bias current can be ignored for a higher
divider string current, but doing so degrades the efficiency at very
light loads.
For the ADP2102-ADJ, the equation for output voltage selection is
V OUT
(V)
0.8
1.0
1.2
1.25
1.375
1.5
1.8
1.875
2.0
R 1
(kΩ)
1
20
49.9
56.2
71.5
88.7
124
133
150
R 2
(kΩ)
80.6
100
100
100
100
100
100
100
100
C FF
(pF)
None
None
None
None
None
None
None
None
15
L
(μH)
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
C IN
(μF)
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
C OUT
(μF)
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
V OUT = V FB (1 + R 1 / R 2 )
where:
V OUT is the output voltage.
(12)
2.5
3.0
3.3
215
274
316
100
100
100
10
8.2
6.8
2.2
2.2
2.2
2.2
2.2
2.2
4.7
4.7
4.7
V FB is the feedback voltage, 0.8 V.
R 1 is the feedback resistor from V OUT to FB.
R 2 is the feedback resistor from FB to GND.
For any adjustable output voltage greater than 1.875 V, a feed-
forward capacitor must be added across R1 for better transient
performance and stability. The formula for calculation of C1 is
EFFICIENCY CONSIDERATIONS
Efficiency is defined as the ratio of output power to input power.
The high efficiency of the ADP2102 has two distinct advantages.
First, only a small amount of power is lost in the dc-to-dc converter
package that reduces thermal constraints. In addition, high effi-
ciency delivers the maximum output power for the given input
C FF = 1/(2π × R1 × f CO /2)
(13)
power, extending battery life in portable applications.
For example, in a 5 V to 3.3 V application, if a 4.7 μF capacitor
is used at the output, a 6.8 pF feed-forward capacitor is recom-
Following are the four major sources of power loss in dc-to-dc
converters like the ADP2102:
mended. The output capacitor value dictates the loop crossover
frequency, f CO . For an output capacitor of 4.7 μF, the loop crossover
frequency is 150 kHz.
The high frequency zero created by C FF and R1 can be very
important for transient load applications. Capacitor C FF provides
?
?
?
?
Power switch conduction losses
Inductor losses
Switching losses
Transition losses
phase lead and functions as a speed-up capacitor to output
voltage changes, so it tends to short out R1 and improve the high
frequency response. This zero tends to produce a positive-going
bump in the phase plot. Ideally, the peak of this bump is centered
over the crossover frequency of the loop. The R1 and C FF zero is
located at
Power Switch Conduction Losses
Power switch conduction losses are caused by the flow of output
current through the P-channel power switch and the N-channel
synchronous rectifier, which have internal resistances (R DS(ON) )
associated with them. The amount of power loss can be approxi-
mated by
f Z = 1/(2π × R1 × C FF )
(14)
P SW_COND = ( R DS (ON)_P × D + R DS (ON) _ N × (1 ? D )) × I OUT2
(15)
The ADP2102-xx (where xx represents the fixed output voltage)
includes the resistive voltage divider internally, reducing the
external circuitry required. For improved load regulation, connect
the FB/OUT to the output voltage as close as possible to the load.
For more information about the ADP2102-ADJ configurations
where D = V OUT / V IN .
The internal resistance of the power switches increases with
in the Typical Performance Characteristics section shows the
change in R DS (ON) vs. input voltage, and Figure 25 shows the change
in R DS (ON) vs. temperature for both power devices.
Rev. B | Page 19 of 24
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ADP2102-3-EVALZ
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ADP2102-4-EVALZ
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ADP2102A-EVALZ
制造商:Analog Devices 功能描述:ADJ OUTPUT FROM 0.8V-1.2V - Bulk
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制造商:Analog Devices 功能描述:ADJ OUTPUT FROM 1.2V-1.5V - Bulk
ADP2102-BL1-EVZ
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制造商:Analog Devices 功能描述:ADJ OUTPUT FROM 1.5V-1.875V - Bulk
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制造商:AD 制造商全称:Analog Devices 功能描述:600mA 3MHz Synchronous Step-Down DC-DC Converter