ADP3051 Просмотр технического описания (PDF) - Analog Devices
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ADP3051 Datasheet PDF : 16 Pages
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ADP3051
APPLICATIONS
RECOMMENDED COMPONENTS
External component selection for the application circuit shown
in Figure 20 depends on the load current requirements. Certain
tradeoffs between different performance parameters can also be
made. Recommended external component values are given in
Table 4.
VIN
CIN
ADP3051
L
4 IN
SW 3
7 SHDN
RA
FB 5
8 GND
COMP 6
PGND
2
C2
RB
RC
C1
VOUT
COUT
Figure 20. Typical Application Circuit
DESIGN PROCEDURE
For applications where specific performance is required, com-
ponent combinations other than those listed in Table 4 may be
more appropriate. A design procedure for selecting the compo-
nents is provided in the following sections.
Setting the Output Voltage
The regulated output voltage of the ADP3051 is set by selecting
the resistive voltage divider formed by RA and RB (see
Figure 21). The voltage divider drops the output voltage to the
voltage at FB by the equation
VOUT
=
VFB
⎜⎛1
⎝
+
RA
RB
⎟⎞
⎠
Where VOUT is the output voltage and VFB is the 0.8 V feedback
regulation threshold. RB controls the voltage divider current,
IDIV, which is calculated by
I DIV
= VFB
RB
Using higher divider current increases accuracy due to the 5 nA
FB input bias current. With RB = 100 kΩ, the accuracy is
degraded by 0.0625%.
For a given RB, choose the value of RA to set the output voltage
by the equation
RA
=
RB
⎜⎛
⎝
VOUT
VFB
− 1⎟⎞
⎠
ADP3051
FB
5
VOUT
RA
gm
COMP
6
RB
REF
ERROR
AMPLIFIER
RC
C2
C1
Figure 21. Typical Compensation Network
Table 4. Recommended External Components for Popular Input/Output Voltage Conditions
(Based on ILOAD = 500 mA Max and a 60 kHz Crossover Frequency)
VIN
VOUT
L (µH)
COUT (µF) CIN (µF)
RA (kΩ)
RB (kΩ)
RC (kΩ)
2.5
1.0
6.8
10
10
2.5
10
4.7
1.8
6.8
10
10
12.5
10
10
3.6
1.0
6.8
10
10
2.5
10
4.7
1.8
8.2
10
10
12.5
10
10
2.5
8.2
10
10
21.3
10
15
5.0
1.0
8.2
10
10
2.5
10
5.7
1.8
10
10
10
12.5
10
10
2.5
10
10
10
21.3
10
15
3.3
12
10
10
31.3
10
18
C1 (pF)
470
270
470
270
180
470
270
180
150
C2 (pF)
47
27
47
27
18
47
27
18
15
Rev. 0 | Page 11 of 16
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