Datasheet LT3463, LT3463A (Analog Devices) - 5

LT3463/LT3463A
U U W U APPLICATIO S I FOR ATIO Choosing an Inductor
such as battery powered applications, use the minimum V Several recommended inductors that work well with the IN value in the above equation. For most regulators with output voltages below 7V, a 4.7µH inductor is the best LT3463 are listed in Table 1, although there are many other choice, even though the equation above might specify a manufacturers and devices that can be used. Consult each smaller value. manufacturer for more detailed information and for their entire selection of related parts. Many different sizes and For higher output voltages, the formula above will give shapes are available. Use the equations and recommenda- large inductance values. For a 3V to 20V converter (typical tions in the next few sections to find the correct inductance LCD Bias application), a 21µH inductor is called for with value for your design. the above equation, but a 10µH inductor could be used
Table 1. Recommended Inductors
without much reduction in the maximum output current.
MAX MAX HEIGHT PART L (
µ
H) I Inductor Selection—Inverting Regulator DC (mA) DCR(
Ω
) (mm) MANUFACTURER
CMD4D06 4.7 750 0.22 0.8 Sumida The formula below calculates the appropriate inductor 10 500 0.46 (847) 956-0666 22 310 1.07 www.sumida.com value to be used for an inverting regulator using the CDRH3D16 10 500 0.19 1.8 Sumida LT3463 (or at least provides a good starting point). This 22 310 0.36 value provides a good tradeoff in inductor size and system LPO4812 4.7 600 0.16 1.2 Coilcraft performance. Pick a standard inductor close to this value 10 400 0.30 (847) 639-6400 22 280 0.64 www.coilcraft.com (both inductors should be the same value). A larger value LQH32C 10 450 0.39 1.8 Murata can be used to slightly increase the available output 15 300 0.75 (714) 852-2001 current, but limit it to around twice the value calculated 22 250 0.92 www.murata.com below, as too large of an inductance will increase the LQH31C 4.7 340 0.85 1.8 Murata output voltage ripple without providing much additional output current. A smaller value can be used (especially for
Inductor Selection—Boost Regulator
systems with output voltages greater than 12V) to give a The formula below calculates the appropriate inductor smaller physical size. Inductance can be calculated as: value to be used for a boost regulator using the LT3463 (or at least provides a good starting point). This value pro-  V + V  OUT D vides a good tradeoff in inductor size and system perfor- L = 2  tOFF  I  mance. Pick a standard inductor close to this value. A LIM   larger value can be used to slightly increase the available output current, but limit it to around twice the value where VD = 0.5V (Schottky diode voltage), ILIM = 250mA calculated below, as too large of an inductance will in- (or 400mA) and tOFF = 300ns. crease the output voltage ripple without providing much For higher output voltages, the formula above will give additional output current. A smaller value can be used large inductance values. For a 3V to 20V converter (typical (especially for systems with output voltages greater than LCD bias application), a 49µH inductor is called for with 12V) to give a smaller physical size. Inductance can be the above equation, but a 10µH or 22µH inductor could be calculated as: used without much reduction in the maximum output current. V − V + V OUT IN MIN D ( ) L = tOFF
Inductor Selection—Inverting Charge Pump Regulator
ILIM For the inverting regulator, the voltage seen by the internal where VD = 0.5V (Schottky diode voltage), ILIM = 250mA power switch is equal to the sum of the absolute value of (or 400mA) and tOFF = 300ns; for designs with varying VIN the input and output voltages, so that generating high 3463f 5