Datasheet

ADP2119/ADP2120 Data Sheet
Rev. A | Page 18 of 24
APPLICATIONS INFORMATION
ADIsimPower DESIGN TOOL
The ADP2119/ADP2120 are supported by ADIsimPower design
tool set. ADIsimPower is a collection of tools that produce
complete power designs optimized for a specific design goal.
The tools enable the user to generate a full schematic, bill of
materials, and calculate performance in minutes. ADIsimPower
can optimize designs for cost, area, efficiency, and parts count
while taking into consideration the operating conditions and
limitations of the IC and all real external components. For
more information about ADIsimPower design tools, refer to
www.analog.com/ADIsimPower. The tool set is available from
this website, and users can also request an unpopulated board
through the tool.
This section describes the selection of the external components
for the ADP2119/ADP2120. The typical application circuit for
the ADP2119 is shown in Figure 50.
10
EN
ADP2119
1
VIN
9
SYNC/MODE
2
PVIN
8
PGOOD
3
SW
7
TRK
4
PGND
6
FB
5
GND
R2
10kΩ
V
IN
5V
C
IN
22µF
X5R
6.3V
C
OUT
22µF
X5R
6.3V
C1
0.1µF
R1
10Ω
R
BOT
15kΩ
V
OUT
2.5V
2A
L
1.5µH
R
TOP
47.5kΩ
08716-050
Figure 50. Typical Application Circuit
OUTPUT VOLTAGE SELECTION
The output voltage of the adjustable version can be set by an
external resistive voltage divider, and the following equation
calculates the output voltage.
)(10.6
BOT
TOP
OUT
R
R
V +×=
To limit the output voltage accuracy degradation due to FB bias
current (0.1 µA maximum) to less than 0.5% (maximum), ensure
that R
BOT
is less than 30 kΩ.
INDUCTOR SELECTION
The inductor value is determined by the operating frequency,
input voltage, output voltage, and ripple current. A small inductor
value leads to a larger inductor current ripple and provides a
faster transient response; however, it degrades efficiency. A
large inductor value leads to a smaller current ripple and good
efficiency but slows the transient response. As a guideline, the
inductor current ripple, ΔI
L
, is typically set to 1/3 of the maximum
load current trade-off between the transient response and efficiency.
The inductor value can be calculated using the following equation:
( )
S
L
OUT
IN
fI
DVV
L
×
×−
=
Δ
where:
V
IN
is the input voltage.
V
OUT
is the output voltage.
ΔI
L
is the inductor current ripple.
D is the duty cycle. D = V
OUT
/V
IN
.
The regulator uses slope compensation in the current loop to
prevent subharmonic oscillations when the duty cycle is larger
than 50%. The internal slope compensation limits the minimum
inductor value.
The negative current limit (−0.6 A) also limits the minimum
inductor value. The inductor current ripple (ΔI
L
) calculated
by the selected inductor should not exceed 1.2 A.
The peak inductor current should be kept below the peak current
limit threshold value and can be calculated from
2
L
OPEAK
I
II
∆
+=
Ensure that the rms current of the selected inductor is greater
than the maximum load current and that its saturation current
is greater than the peak current limit of the regulator.
OUTPUT CAPACITOR SELECTION
The output voltage ripple, load step transient, and loop stability
determine the output capacitor selection.
The ESR and the capacitance determine the output ripple.








××
+×∆=∆
S
OUT
L
OUT
fC
ESRIV
8
1
The load transient response depends on the inductor, the output
capacitor, and the control loop.
The ADP2119/ADP2120 have integrated loop compensation to
provide a simple power solution design. Table 5 and Table 6 show
the typical recommended inductors and capacitors for the ADP2119/
ADP2120. X5R or X7R ceramic capacitors are highly recommended.
Table 5. Recommended L and C
OUT
Values for the ADP2119
V
IN
(V)
V
OUT
(V)
L (µH)
C
OUT
(µF)
3.3 1.0 1 22 + 22
3.3 1.2 1 22 + 22
3.3 1.5 1 22 + 10
3.3 1.8 1 22
3.3 2.5 1 22
5 1.0 1 22 + 22
5 1.2 1.5 22 + 22
5 1.5 1.5 22 +10
5 1.8 1.5 22 +10
5 2.5 1.5 22
5
3.3
1.5
22