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LT3463

Dual Micropower DC/DC Converters with Schottky Diodes

Linear Technology 

LT3463/LT3463A

APPLICATIO S I FOR ATIO

Choosing an Inductor

Several recommended inductors that work well with the

LT3463 are listed in Table 1, although there are many other

manufacturers and devices that can be used. Consult each

manufacturer for more detailed information and for their

entire selection of related parts. Many different sizes and

shapes are available. Use the equations and recommenda-

tions in the next few sections to find the correct inductance

value for your design.

Table 1. Recommended Inductors

PART

CMD4D06

MAX MAX HEIGHT

L (µH) IDC (mA) DCR(Ω) (mm) MANUFACTURER

4.7 750 0.22 0.8 Sumida

10 500 0.46

(847) 956-0666

22 310 1.07

www.sumida.com

CDRH3D16

10 500 0.19 1.8 Sumida

22 310 0.36

LPO4812

4.7 600 0.16 1.2 Coilcraft

10 400 0.30

(847) 639-6400

22 280 0.64

www.coilcraft.com

LQH32C

10 450 0.39 1.8 Murata

15 300 0.75

(714) 852-2001

22 250 0.92

www.murata.com

LQH31C

4.7 340 0.85 1.8 Murata

Inductor Selection—Boost Regulator

The formula below calculates the appropriate inductor

value to be used for a boost regulator using the LT3463 (or

at least provides a good starting point). This value pro-

vides a good tradeoff in inductor size and system perfor-

mance. Pick a standard inductor close to this value. A

larger value can be used to slightly increase the available

output current, but limit it to around twice the value

calculated below, as too large of an inductance will in-

crease the output voltage ripple without providing much

additional output current. A smaller value can be used

(especially for systems with output voltages greater than

12V) to give a smaller physical size. Inductance can be

calculated as:

( ) VOUT − VIN MIN + VD

L=

ILIM

tOFF

where VD = 0.5V (Schottky diode voltage), ILIM = 250mA

(or 400mA) and tOFF = 300ns; for designs with varying VIN

such as battery powered applications, use the minimum

VIN value in the above equation. For most regulators with

output voltages below 7V, a 4.7µH inductor is the best

choice, even though the equation above might specify a

smaller value.

For higher output voltages, the formula above will give

large inductance values. For a 3V to 20V converter (typical

LCD Bias application), a 21µH inductor is called for with

the above equation, but a 10µH inductor could be used

without much reduction in the maximum output current.

Inductor Selection—Inverting Regulator

The formula below calculates the appropriate inductor

value to be used for an inverting regulator using the

LT3463 (or at least provides a good starting point). This

value provides a good tradeoff in inductor size and system

performance. Pick a standard inductor close to this value

(both inductors should be the same value). A larger value

can be used to slightly increase the available output

current, but limit it to around twice the value calculated

below, as too large of an inductance will increase the

output voltage ripple without providing much additional

output current. A smaller value can be used (especially for

systems with output voltages greater than 12V) to give a

smaller physical size. Inductance can be calculated as:

 VOUT + VD 

L = 2 ILIM

 tOFF

where VD = 0.5V (Schottky diode voltage), ILIM = 250mA

(or 400mA) and tOFF = 300ns.

For higher output voltages, the formula above will give

large inductance values. For a 3V to 20V converter (typical

LCD bias application), a 49µH inductor is called for with

the above equation, but a 10µH or 22µH inductor could be

used without much reduction in the maximum output

current.

Inductor Selection—Inverting Charge Pump Regulator

For the inverting regulator, the voltage seen by the internal

power switch is equal to the sum of the absolute value of

the input and output voltages, so that generating high

3463f

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