ADP2114 Analog Devices, ADP2114 Datasheet - Page 27

• Manufacturer Part Number: ADP2114
• Description: Configurable, Dual 2 A/Single 4 A, Synchronous Step-Down DC-to-DC Regulator
• Manufacturer: Analog Devices

EXTERNAL COMPONENTS SELECTION
INPUT CAPACITOR SELECTION
The input current to a buck converter is pulsating in nature. The
current is zero when the high-side switch is off and approximately
equal to the load current when it is on. Because this occurs at
reasonably high frequencies (300 kHz to 1.2 MHz), the input
bypass capacitor ends up supplying most of the high frequency
current (ripple current), allowing the input power source to
supply only the average (dc) current. The input capacitor needs a
sufficient ripple current rating to handle the input ripple as well
as an ESR that is low enough to mitigate the input voltage
ripple. For the ADP2114, place a 22 μF, 6.3 V, X5R ceramic
capacitor close to the VINx pin for each channel. X5R or X7R
dielectrics are recommended with a voltage rating of 6.3 V or
10 V. Y5V and Z5U dielectrics are not recommended due to
their poor temperature and dc bias characteristics.
VDD RC FILTER
It is recommended to apply the input power, V
through a low-pass RC filter, as shown on Figure 76. Connecting a
10 Ω resistor in series with V
ceramic capacitor between VDD and GND creates a 16 kHz
(−3 dB) low-pass filter that effectively attenuates voltage glitches
on the input power rail caused by the switching regulator. This
provides a clean power supply to the internal, sensitive, analog
and digital circuits in the ADP2114, ensuring robust operation.
INDUCTOR SELECTION
The high switching frequency of ADP2114 allows for minimal
output voltage ripple even with small inductors. The sizing of the
inductor is a trade-off between efficiency and transient response. A
small inductor leads to larger inductor current ripple that provides
excellent transient response but degrades efficiency. Due to
the high switching frequency of ADP2114, shielded ferrite core
inductors are recommended for their low core losses and low EMI.
As a guideline, the inductor peak-to-peak current ripple, ΔI
typically set to 1/3 of the maximum load current for optimal
transient response and efficiency.
where:
V
V
f
SW
IN
OUT
is the converter switching frequency.
is the input voltage on the VINx terminal.
Δ
⇒
is the desired output voltage.
I
L
L
=
IDEAL
V
OUT
V
=
IN
×
3
f
V
(
×
Figure 76. Low-Pass Filter at VDD
×
SW
V
IN
V
f
IN
SW
OUT
×
V
−
10Ω
×
1µF
IN
V
×
L
OUT
(
×
V
I
IN
IN
)
LOAD
and a 1 μF, 6.3 V, X5R (or X7R)
≈
−
VDD
GND
ADP2114
V
I
(
MAX
LOAD
OUT
3
)
)
(MAX
)
IN
, to the VDD pin
L
, is
Rev. 0 | Page 27 of 40
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The internal slope compensation introduces additional limitations
on the optimal inductor value for stable operation because the
internal ramp is scaled for each V
different V
Table 8. Minimum and Maximum Inductor Values
f
300
300
300
300
300
300
300
300
300
300
300
600
600
600
600
600
600
600
600
600
600
600
1200
1200
1200
1200
1200
1200
1200
1200
1200
To avoid saturation, the rated current of the inductor has to be
larger than the maximum peak inductor I
where:
I
ΔI
SW
LOAD_MAX
L
(kHz)
is the inductor ripple current (peak to peak).
I
L
_
PEAK
is the maximum dc load current.
IN
, V
V
5
5
3.3
5
3.3
5
3.3
5
3.3
5
3.3
5
5
3.3
5
3.3
5
3.3
5
3.3
5
3.3
5
5
3.3
5
3.3
5
3.3
5
3.3
=
IN
I
OUT
(V)
LOAD
, and f
_
MAX
SW
V
3.3
2.5
2.5
1.8
1.8
1.5
1.5
1.2
1.2
0.8
0.8
3.3
2.5
2.5
1.8
1.8
1.5
1.5
1.2
1.2
0.8
0.8
2.5
1.8
1.8
1.5
1.5
1.2
1.2
0.8
0.8
+
OUT
combinations are listed in Table 8.
Δ
2
I
(V)
L
OUT
Min L (μH)
6.8
5.6
5.6
4.7
4.7
2.2
2.2
2.2
2.2
1.5
1.5
3.3
3.3
3.3
2.2
2.2
1.5
1.5
1.5
1.5
1.0
1.0
1.0
1.0
1.0
0.8
0.8
0.8
0.8
0.47
0.47
setting. The limits for
L_PEAK
current given by
ADP2114
Max L (μH)
10
15
6.8
12
8.2
12
8.2
10
8.2
6.8
6.8
4.7
6.8
3.3
6.8
3.3
5.6
4.7
4.7
3.3
3.3
3.3
3.3
3.3
2.2
2.2
2.2
2.2
2.2
1.5
1.5
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