Datasheet
ADP1650
Rev. C | Page 26 of 32
APPLICATIONS INFORMATION
EXTERNAL COMPONENT SELECTION
Selecting the Inductor
The ADP1650 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 the inductor ripple current. A
reduction in the effective inductance due to saturation increases
the inductor current ripple. Table 18 provides a list of recom-
mended inductors.
Selecting the Input Capacitor
The ADP1650 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
characteristics of ceramic capacitors, 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 ADP1650 as possible. As with the output
capacitor, a low ESR capacitor is required. Table 19 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 NFET power switch on period. It also
stabilizes the loop. The recommended capacitor is a 10 µF, 6.3 V,
X5R/X7R ceramic capacitor.
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 20 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 due to
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 18. Suggested Inductors
Vendor Value (µH) Part No. DCR (mΩ) ISAT (A) Dimensions L × W × H (mm)
Toko 1.0 FDSD0312 41.5 4.5 3.0 × 3.0 × 1.2
Toko 1.0 DFE2520 50 3.4 2.5 × 2.0 × 1.2
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
FDK 1.0 MIPS3226D 40 3 2.5 × 2.0 × 1.2
Table 19. 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 20. 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