TMS320F280041: Inductor requirements for internal 1.2-V switching regulator (DC-DC)

Sebastian Ausserwoeger

Hi,

we are currently working on a design with the TMS320F280041, where we want to use the internal 1.2V switching regulator for efficiency reasons. Currently, the choice of a suitable power inductor for the DC-DC converter (I guess it's a simple buck converter?) gives me a little headache.

Referring to Table 5-5 in the TMS320F28004x datasheet, the requirement for a DCR of 80 mOhms ±25% seems quite stringent to me. According to Table 5-1 worst case IDD power consumption is below 100mA, so conduction losses in the power inductor would be <10mW, even with 10x the specified DCR.

Virtually all feasible low-cost 2.2µH power inductors coming in a standard 0806 or 1008 footprint exhibit rated currents of >2A, with a typical DCR range of 100-150 mOhms. So, is it really necessary to maintain a DCR of 80 mOhms ±25% under all circumstances? Since this requirement drastically reduces the amount of suitable inductors (and increases costs).

Thanks and best regards,

Sebastian

over 5 years ago

0 Frank Ankapong over 5 years ago

TI__Mastermind 28275 points

Hi Sebastian,

The DCR is a loose requirement. However, the DCR is not only for efficiency as it also creates a small offset on the output. This offset can take the final DCDC output out of the recommended operating range for VDD. Nevertheless 100-150 mOhms should be fine.

0 Sebastian Ausserwoeger over 5 years ago in reply to Frank Ankapong

Prodigy 230 points

Hi Frank.

Thank you for the quick response. We will evaluate the offset.

Best regards,

Sebastian

C2000™︎ microcontrollers

C2000 microcontrollers forum

TMS320F280041: Inductor requirements for internal 1.2-V switching regulator (DC-DC)