ADP5023 Analog Devices, ADP5023 Datasheet - Page 21

• Manufacturer Part Number: ADP5023
• Description: Dual 3 MHz, 800 mA Buck Regulator with One 300 mA LDO
• Manufacturer: Analog Devices

Data Sheet
APPLICATIONS INFORMATION
BUCK EXTERNAL COMPONENT SELECTION
Trade-offs between performance parameters such as efficiency
and transient response can be made by varying the choice of
external components in the applications circuit, as shown in
Figure 1.
Feedback Resistors
For the adjustable model, referring to Figure 47, the total
combined resistance for R1 and R2 is not to exceed 400 kΩ.
Inductor
The high switching frequency of the
selection of small chip inductors. For best performance, use
inductor values between 0.7 μH and 3 μH. Suggested inductors
are shown in Table 8.
The peak-to-peak inductor current ripple is calculated using
the following equation:
where:
f
L is the inductor value.
The minimum dc current rating of the inductor must be greater
than the inductor peak current. The inductor peak current is
calculated using the following equation:
Inductor conduction losses are caused by the flow of current
through the inductor, which has an associated internal dc
resistance (DCR). Larger sized inductors have smaller DCR,
which may decrease inductor conduction losses. Inductor core
losses are related to the magnetic permeability of the core material.
Because the bucks are high switching frequency dc-to-dc
converters, shielded ferrite core material is recommended for
its low core losses and low EMI.
Output Capacitor
Higher output capacitor values reduce the output voltage ripple
and improve load transient response. When choosing this value,
it is also important to account for the loss of capacitance due to
output voltage dc bias.
Table 8. Suggested 1.0 μH Inductors
Vendor
Murata
Murata
Taiyo Yuden
Coilcraft
Coilcraft
Toko
SW
is the switching frequency.
I
I
RIPPLE
PEAK
=
=
I
LOAD
V
OUT
V
(
MAX
IN
×
(
×
V
)
IN
f
+
SW
I
−
RIPPLE
×
V
2
Model
LQM2MPN1R0NG0B
LQM18FN1R0M00B
CBC3225T1R0MR
XFL4020-102ME
XPL2010-102ML
MDT2520-CN
L
OUT
)
ADP5023
bucks allows the
Rev. A | Page 21 of 28
Dimensions (mm)
2.0 × 1.6 × 0.9
3.2 × 2.5 × 1.5
3.2 × 2.5 × 2.5
4.0 × 4.0 × 2.1
1.9 × 2.0 × 1.0
2.5 × 2.0 × 1.2
Ceramic capacitors are manufactured with a variety of dielec-
trics, each with a different behavior over temperature and
applied voltage. Capacitors must have a dielectric adequate
to ensure the minimum capacitance over the necessary
temperature range and dc bias conditions. X5R or X7R
dielectrics with a voltage rating of 6.3 V or 10 V are recom-
mended for best performance. Y5V and Z5U dielectrics are
not recommended for use with any dc-to-dc converter because
of their poor temperature and dc bias characteristics.
The worst-case capacitance accounting for capacitor variation
over temperature, component tolerance, and voltage is calcu-
lated using the following equation:
where:
C
TEMPCO is the worst-case capacitor temperature coefficient.
TOL is the worst-case component tolerance.
In this example, the worst-case temperature coefficient
(TEMPCO) over −40°C to +85°C is assumed to be 15% for an
X5R dielectric. The tolerance of the capacitor (TOL) is assumed
to be 10% and C
Substituting these values in the equation yields
To guarantee the performance of the bucks, it is imperative
that the effects of dc bias, temperature, and tolerances on the
behavior of the capacitors be evaluated for each application.
EFF
is the effective capacitance at the operating voltage.
C
C
EFF
EFF
12
10
8
6
4
2
0
0
= C
= 9.2 μF × (1 − 0.15) × (1 − 0.1) = 7.0 μF
Figure 49. Capacitance vs. Voltage Characteristic
OUT
× (1 − TEMPCO) × (1 − TOL)
OUT
1
is 9.2 μF at 1.8 V, as shown in Figure 49.
2
DC BIAS VOLTAGE (V)
I
1400
2300
2000
5400
3750
1350
3
SAT
(mA)
4
5
ADP5023
DCR (mΩ)
85
54
71
11
89
85
6