Here explains how to confirm the coil current using DC/DC simulation and an example of selection of an optimum coil.
1. Execution of simulation (select the IC / input the power supply specifications)
Input the simulation conditions for input items and execute simulation.
Step 1. Select a product
Step 2. Select oscillation frequency
Step 3. Select an operation mode
Step 4. Input the power supply specifications (Vin / Vout / Iout / peripheral component values etc.)
2. How to confirm the coil current / how to select a coil
It is possible to confirm the coil current from "Summary" tab, "Waveform" tab, or "Coil Current / Input Current" tab. For coil current / amplitude at each output current, confirm "Coil Current / Input Current" tab.
A coil is generally selected based on the maximum current flowing in the coil.
Referencing the simulation result shown above, whole the maximum value of coil current is 600mA, a coil with at least 1.5 to 2.0 times higher saturation current is generally selected.For an inductance value, select a recommended inductance value shown in the datasheet of the DC/DC converter to be used.
CAUTIONS
The selection criteria are not the output current, but the current flowing in the coil current.
With DC/DC converter, output current and coil current do not indicate the same current value. Especially for Topology of other than non-isolated step-down DC/DC converter, the maximum value of the coil current tends to be considerably higher than the output current.
When you manually calculate the maximum value of the coil current, it is necessary to conduct a complicated calculation after understanding individual IC control. For this reason, obtaining the maximum current of the coil under actual specification conditions through simulation, etc. is effective for man-hour reduction or suppression of part selection error.