LM2676
SNVS031J –APRIL 2000–REVISED APRIL 2013
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Step 3: Use the nomograph for the 3.3V device, Figure 21. The intersection of the 16V horizontal line (Vin max)
and the 2.5A vertical line (Iload max) indicates that L33, a 22μH inductor, is required.
From Table 1, L33 in a through-hole component is available from Renco with part number RL-1283-22-43 or part
number PE-53933 from Pulse Engineering.
Step 4: Use Table 6 or Table 7 to determine an output capacitor. With a 3.3V output and a 22μH inductor there
are four through-hole output capacitor solutions with the number of same type capacitors to be paralleled and an
identifying capacitor code given. Table 3 or Table 4 provide the actual capacitor characteristics. Any of the
following choices will work in the circuit:
1 x 220μF/10V Sanyo OS-CON (code C5)
1 x 1000μF/35V Sanyo MV-GX (code C10)
1 x 2200μF/10V Nichicon PL (code C5)
1 x 1000μF/35V Panasonic HFQ (code C7)
Step 5: Use Table 8 or Table 9 to select an input capacitor. With 3.3V output and 22μH there are three through-
hole solutions. These capacitors provide a sufficient voltage rating and an rms current rating greater than 1.25A
(1/2 Iload max). Again using Table 3 or Table 4 for specific component characteristics the following choices are
suitable:
1 x 1000μF/63V Sanyo MV-GX (code C14)
1 x 820μF/63V Nichicon PL (code C24)
1 x 560μF/50V Panasonic HFQ (code C13)
Step 6: From Table 10 a 3A Schottky diode must be selected. For through-hole components 20V rated diodes
are sufficient and 2 part types are suitable:
1N5820
SR302
Step 7: A 0.01μF capacitor will be used for Cboost.
ADJUSTABLE OUTPUT DESIGN EXAMPLE
In this example it is desired to convert the voltage from a two battery automotive power supply (voltage range of
20V to 28V, typical in large truck applications) to the 14.8VDC alternator supply typically used to power electronic
equipment from single battery 12V vehicle systems. The load current required is 2A maximum. It is also desired
to implement the power supply with all surface mount components.
Step 1: Operating conditions are:
Vout = 14.8V
Vin max = 28V
Iload max = 2A
14
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