ADP5042 Analog Devices, ADP5042 Datasheet - Page 23

• Manufacturer Part Number: ADP5042
• Description: Micro PMU with 0.8 A Buck, Two 300 mA LDOs, Supervisory, Watchdog and Manual Reset
• 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 66.
Inductor
The high switching frequency of the ADP5042 buck allows for
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 11.
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 buck is high switching frequency dc-to-dc converters,
shielded ferrite core material is recommended for its low core
losses and low EMI.
Table 11. Suggested 1.0 μH Inductors
Vendor
Murata
Murata
Taiyo Yuden
Coilcraft
TDK
Coilcraft
Toko
SW
is the switching frequency.
I
I
RIPPLE
PEAK
=
=
I
LOAD
Model
LQM2MPN1R0NG0B
LQM18FN1R0M00B
CBMF1608T1R0M
EPL2014-102ML
GLFR1608T1R0M-LR
0603LS-102
MDT2520-CN
V
OUT
V
(
MAX
IN
×
(
×
V
)
f
IN
+
SW
I
−
RIPPLE
×
V
2
L
OUT
)
Dimensions
(mm)
2.0 × 1.6 × 0.9
1.6 × 0.8 × 0.8
1.6 × 0.8 × 0.8
2.0 × 2.0 × 1.4
1.6 × 0.8 × 0.8
1.8 × 1.69 × 1.1
2.5 × 2.0 × 1.2
I
(mA)
1400
150
290
900
230
400
1350
SAT
Rev. A | Page 23 of 32
DCR
(mΩ)
85
26
90
59
80
81
85
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 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 buck, it is imperative
that the effects of dc bias, temperature, and tolerances on the
behavior of the capacitors be evaluated for each application.
EFF
OUT
is the effective capacitance at the operating voltage.
C
C
is 9.2481 μF at 1.8 V, as shown in Figure 61.
EFF
EFF
12
10
8
6
4
2
0
0
= C
= 9.2481 μF × (1 − 0.15) × (1 − 0.1) = 7.0747 μF
OUT
Figure 61. Typical Capacitor Performance
× (1 − TEMPCO) × (1 − TOL)
1
2
DC BIAS VOLTAGE (V)
3
4
5
ADP5042
6