Datasheet
Data Sheet ADP1649
Rev. 0 | Page 25 of 28
APPLICATIONS INFORMATION
EXTERNAL COMPONENT SELECTION
Selecting the Inductor
The ADP1649 boost converter increases the battery voltage
to allow driving of one LED, whose voltage drop is higher than
the battery voltage plus the current source headroom voltage.
This allows the converter to regulate the LED current over the
entire battery voltage range and with a wide variation of LED
forward voltage.
The inductor saturation current should be greater than the sum
of the dc input current and half of the inductor ripple current. A
reduction in the effective inductance due to saturation increases
the inductor current ripple. Table 19 provides a list of recom-
mended inductors.
Selecting the Input Capacitor
The ADP1649 requires an input bypass capacitor to supply
transient currents while maintaining constant input and output
voltages. The input capacitor carries the input ripple current,
allowing the input power source to supply only the dc current.
Increased input capacitance reduces the amplitude of the switching
frequency ripple on the battery. Due to the dc bias characteris-
tics of ceramic capacitors, the use of a 0603, 6.3 V, X5R/X7R,
10 µF ceramic capacitor is preferable. Higher value input
capacitors help to reduce the input voltage ripple and improve
transient response.
To minimize supply noise, place the input capacitor as close to
the VIN pin of the ADP1649 as possible. A low ESR capacitor is
required. Table 20 provides a list of suggested input capacitors.
Selecting the Output Capacitor
The output capacitor maintains the output voltage and supplies
the LED current during the period when the NFET power
switch is on. The output capacitor also stabilizes the loop. The
recommended output capacitor is a 10 µF, 6.3 V, X5R/X7R
ceramic capacitor with low ESR.
Note that dc bias characterization data is available from capa-
citor manufacturers and should be taken into account when
selecting input and output capacitors. The 6.3 V capacitors are
best for most designs. Table 21 provides a list of recommended
output capacitors.
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 caused
by output voltage dc bias.
Ceramic capacitors have a variety of dielectrics, each with different
behavior over temperature and applied voltage. Capacitors must
have a dielectric that ensures 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 recom-
mended for use with any dc-to-dc converter because of their
poor temperature and dc bias characteristics.
Table 19. Suggested Inductors
Vendor Value (µH) Part No. DCR (mΩ) I
SAT
(A) Dimensions L × W × H (mm)
Coilcraft 1.0 XFL3010 43 2.4 3.0 × 3.0 × 1.0
Murata
1.0
LQM32P_G0
60
3
3.2 × 2.5 × 1.0
Wurth 1.0 744028001 65 1.5 2.8 × 2.8 × 1.1
Taiyo Yuden 1.0 NR 3015T 1R0N 36 2.1 3.0 × 3.0 × 1.5
FDK 1.0 MIP3226D 40 3 2.5 × 2.0 × 1.2
Table 20. Suggested Input Capacitors
Vendor Value Part No. Dimensions L × W × H (mm)
Murata 10 µF, 6.3 V GRM188R60J106ME47 1.6 × 0.8 × 0.8
TDK 10 µF, 6.3 V C1608JB0J106K 1.6 × 0.8 × 0.8
Taiyo Yuden 10 µF, 6.3 V JMK107BJ106MA 1.6 × 0.8 × 0.8
Table 21. Suggested Output Capacitors
Vendor Value Part No. Dimensions L × W × H (mm)
Murata 10 µF, 6.3 V GRM188R60J106ME47 1.6 × 0.8 × 0.8
TDK 10 µF, 6.3 V C1608JB0J106K 1.6 × 0.8 × 0.8
Taiyo Yuden 10 µF, 6.3 V JMK107BJ106MA 1.6 × 0.8 × 0.8