LM2679_15 Datasheet, PDF (16/35 Pages) Texas Instruments – LM2679 SIMPLE SWITCHER® 5A Step-Down Voltage Regulator with Adjustable Current

LM2679
SNVS026N – MARCH 2000 – REVISED APRIL 2013
www.ti.com
Step 4: Use Table 12 and Table 13 to determine an output capacitor. With a 14.8V output the 12.5 to 15V row is
used and with a 47μH inductor there are three surface mount output capacitor solutions. Table 3 and Table 4
provide the actual capacitor characteristics based on the C Code number. Any of the following choices can be
used:
1 x 33μF/20V AVX TPS (code C6)
1 x 47μF/20V Sprague 594 (code C8)
1 x 47μF/20V Kemet T495 (code C8)
NOTE
When using the adjustable device in low voltage applications (less than 3V output), if the
nomograph, Figure 21, selects an inductance of 22μH or less, Table 12 and Table 13 do
not provide an output capacitor solution. With these conditions the number of output
capacitors required for stable operation becomes impractical. It is recommended to use
either a 33μH or 47μH inductor and the output capacitors from Table 12 and Table 13.
Step 5: An input capacitor for this example will require at least a 35V WV rating with an rms current rating of
1.75A (1/2 Iout max). From Table 3 and Table 4, it can be seen that C12, a 33μF/35V capacitor from Sprague,
has the highest voltage/current rating of the surface mount components and that two of these capacitor in parallel
will be adequate.
Step 6: From Table 10, a 5A or more Schottky diode must be selected. For surface mount diodes with a margin
of safety on the voltage rating one of two diodes can be used:
MBRD1545CT
6TQ045S
Step 7: A 0.01μF capacitor will be used for Cboost.
The softstart pin will be left open circuited.
Step 8: Determine a value for R_ADJ to provide a peak switch current limit of at least 3.5A plus 50% or 5.25A.
(8)
Use a value of 7.15KΩ.
VSON PACKAGE DEVICES
The LM2679 is offered in the 14 lead VSON surface mount package to allow for a significantly decreased
footprint with equivalent power dissipation compared to the DDPAK.
The Die Attach Pad (DAP) can and should be connected to PCB Ground plane/island. For CAD and assembly
guidelines refer to Application Note AN-1187 at www.ti.com/lsds/ti/analog/powermanagement/power_portal.page.
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