ADP1650ACBZ-R7 datasheet(26/32 Pages) AD

26 / 32 page

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

3.4

2.5 × 2.0 × 1.2

Coilcraft

1.0

XFL3010

2.4

3.0 × 3.0 × 1.0

Murata

1.0

LQM32P_G0

3.2 × 2.5 × 1.0

FDK

1.0

MIPS3226D

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

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