ADP5033 Analog Devices, ADP5033 Datasheet - Page 20

• Manufacturer Part Number: ADP5033
• Description: Dual 3 MHz, 800 mA Buck Regulators with Two 300 mA LDOs
• Manufacturer: Analog Devices

ADP5033
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.
Inductor
The high switching frequency of the
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.
Table 8. Suggested 1.0 μH Inductors
Vendor
Murata
Murata
Taiyo Yuden
Coilcraft
TDK
Coilcraft
Toko
SW
is the switching frequency.
I
I
RIPPLE
PEAK
=
=
I
Model
LQM2MPN1R0NG0B 2.0 × 1.6 × 0.9
LQM18FN1R0M00B
BRC1608T1R0M
EPL2014-102ML
GLFR1608T1R0M-LR 1.6 × 0.8 × 0.8
0603LS-102
MDT2520-CN
V
LOAD
OUT
V
(
MAX
IN
×
(
×
V
)
f
IN
+
SW
I
−
RIPPLE
×
V
2
L
OUT
)
Dimensions
(mm)
1.6 × 0.8 × 0.8
1.6 × 0.8 × 0.8
2.0 × 2.0 × 1.4
1.8 × 1.69 × 1.1
2.5 × 2.0 × 1.2
ADP5033
bucks allows for
I
(mA)
1400
150
520
900
230
400
1350
SAT
DCR
(mΩ)
85
26
180
59
80
81
85
Rev. A | Page 20 of 28
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.
Ceramic capacitors are manufactured with a variety of dielectrics,
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 recommended 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 calculated
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
OUT
Figure 45. Typical Capacitor Performance
× (1 − TEMPCO) × (1 − TOL)
1
OUT
is 9.2 μF at 1.8 V, as shown in Figure 45.
2
DC BIAS VOLTAGE (V)
3
4
Data Sheet
5
6