ADP2106-1.8-EVALZ Analog Devices Inc, ADP2106-1.8-EVALZ Datasheet - Page 18

• Manufacturer Part Number: ADP2106-1.8-EVALZ
• Description: BOARD EVAL FOR ADP2106-1.8
• Manufacturer: Analog Devices Inc

Specifications of ADP2106-1.8-EVALZ

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.8V
• Current - Output: 1.5A
• Voltage - Input: 2.7 ~ 5.5V
• Regulator Topology: Buck
• Frequency - Switching: 1.2MHz
• Board Type: Fully Populated
• Utilized Ic / Part: ADP2106
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

ADP2105/ADP2106/ADP2107
OUTPUT CAPACITOR SELECTION
The output capacitor selection affects both the output voltage ripple
and the loop dynamics of the converter. For a given loop crossover
frequency (the frequency at which the loop gain drops to 0 dB), the
maximum voltage transient excursion (overshoot) is inversely
proportional to the value of the output capacitor. Therefore, larger
output capacitors result in improved load transient response. To
minimize the effects of the dc-to-dc converter switching, the cross-
over frequency of the compensation loop should be less than 1/10
of the switching frequency. Higher crossover frequency leads to
faster settling time for a load transient response, but it can also
cause ringing due to poor phase margin. Lower crossover
frequency helps to provide stable operation but needs large output
capacitors to achieve competitive overshoot specifications.
Therefore, the optimal crossover frequency for the control loop of
ADP2105/ADP2106/ADP2107 is 80 kHz, 1/15 of the switching
frequency. For a crossover frequency of 80 kHz, Figure 39 shows
the maximum output voltage excursion during a 1 A load transient,
as the product of the output voltage and the output capacitor is
varied. Choose the output capacitor based on the desired load
transient response and target output voltage.
For example, if the desired 1 A load transient response (overshoot)
is 5% for an output voltage of 2.5 V, then from Figure 39
The ADP2105/ADP2106/ADP2107 have been designed for
operation with small ceramic output capacitors that have low
ESR and ESL. Therefore, they are comfortably able to meet tight
output voltage ripple specifications. 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. Table 10 shows a list of recommended
MLCC capacitors from Murata and Taiyo Yuden.
Figure 39. Percentage Overshoot for a 1 A Load Transient Response vs.
Output Capacitor × Output Voltage = 50 μC
⇒
Output
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
15
20
Capacitor
OUTPUT CAPACITOR × OUTPUT VOLTAGE (μC)
Output Capacitor × Output Voltage
25
30
=
35
50
2
40
5 .
μ
C
45
≈
20
50
μ
F
55
60
65
70
Rev. C | Page 18 of 36
When choosing output capacitors, it is also important to
account for the loss of capacitance due to output voltage dc bias.
Figure 40 shows the loss of capacitance due to output voltage dc
bias for three X5R MLCC capacitors from Murata.
For example, to get 20 μF output capacitance at an output voltage
of 2.5 V, based on Figure 40, as well as to give some margin for
temperature variance, a 22 μF and a 10 μF capacitor are to be
used in parallel to ensure that the output capacitance is sufficient
under all conditions for stable behavior.
Table 10. Recommended Input and Output Capacitor
Selection for the ADP2105/ADP2106/ADP2107
Capacitor
4.7 μF, 10 V
10 μF, 10 V
22 μF, 6.3 V
INPUT CAPACITOR SELECTION
The input capacitor reduces input voltage ripple caused by the
switch currents on the PWIN pins. Place the input capacitors as
close as possible to the PWIN pins. Select an input capacitor
capable of withstanding the rms input current for the maximum
load current in your application.
For the ADP2105, it is recommended that each PWIN pin be
bypassed with a 4.7 μF or larger input capacitor. For the ADP2106,
bypass each PWIN pin with a 10 μF and a 4.7 μF capacitor, and
for the ADP2107, bypass each PWIN pin with a 10 μF capacitor.
As with the output capacitor, a low ESR ceramic capacitor is
recommended to minimize input voltage ripple. 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. Refer to
Table 10 for input capacitor recommendations.
X5R 0805
X5R 0805
X5R 0805
Figure 40. Percentage Drop-In Capacitance vs. DC Bias for Ceramic
–100
–20
–40
–60
–80
Capacitors (Information Provided by Murata Corporation)
20
0
0
1
2
3
4.7µF 0805 X5R MURATA GRM21BR61A475K
10µF 0805 X5R MURATA GRM21BR61A106K
22µF 0805 X5R MURATA GRM21BR60J226M
Murata
GRM21BR61A475K
GRM21BR61A106K
GRM21BR60J226M
2
VOLTAGE (V
Vendor
DC
3
)
4
Taiyo Yuden
LMK212BJ475KG
LMK212BJ106KG
JMK212BJ226MG
2
1
6