ADP5042

Manufacturer Part NumberADP5042
DescriptionMicro PMU with 0.8 A Buck, Two 300 mA LDOs, Supervisory, Watchdog and Manual Reset
ManufacturerAnalog Devices
ADP5042 datasheet
 


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Page 21
22
Page 22
23
Page 23
24
Page 24
25
Page 25
26
Page 26
27
Page 27
28
Page 28
29
Page 29
30
Page 30
31
32
Page 23/32

Download datasheet (2Mb)Embed
PrevNext
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:
×
V
(
V
V
)
=
OUT
IN
OUT
I
RIPPLE
×
×
V
f
L
IN
SW
where:
f
is the switching frequency.
SW
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:
I
=
+
RIPPLE
I
I
PEAK
LOAD
(
MAX
)
2
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
Dimensions
Vendor
Model
(mm)
Murata
LQM2MPN1R0NG0B
2.0 × 1.6 × 0.9
Murata
LQM18FN1R0M00B
1.6 × 0.8 × 0.8
Taiyo Yuden
CBMF1608T1R0M
1.6 × 0.8 × 0.8
Coilcraft
EPL2014-102ML
2.0 × 2.0 × 1.4
TDK
GLFR1608T1R0M-LR
1.6 × 0.8 × 0.8
Coilcraft
0603LS-102
1.8 × 1.69 × 1.1
Toko
MDT2520-CN
2.5 × 2.0 × 1.2
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:
C
= C
EFF
OUT
where:
C
is the effective capacitance at the operating voltage.
EFF
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
is 9.2481 μF at 1.8 V, as shown in Figure 61.
OUT
Substituting these values in the equation yields
C
= 9.2481 μF × (1 − 0.15) × (1 − 0.1) = 7.0747 μF
EFF
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.
12
I
DCR
SAT
(mA)
(mΩ)
10
1400
85
150
26
8
290
90
900
59
6
230
80
400
81
4
1350
85
2
0
0
Figure 61. Typical Capacitor Performance
Rev. A | Page 23 of 32
ADP5042
× (1 − TEMPCO) × (1 − TOL)
1
2
3
4
5
6
DC BIAS VOLTAGE (V)