• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 38 subscribers
  • Views 798 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

WEBENCH® Tools: About Inductor current ripple of LM5018 on WEBENCH

Tao_2199
Genius 5770 points
Other Parts Discussed in Thread: LM5018

Tool/software: WEBENCH® Design Tools

Hello,

 

Regarding to Inductor current ripple of LM5018 on WEBENCH, I have a question.

My condition:

Vin=55V,Vout=46V,Iout(max)=30mA, fsw=544kHz

 

Generally, the inductor ripple current(typ) is following.

 

Inductor ripple current (typ) = 0.3(30%) x Iout(max)

In this case, 0.3 x 0.03A = 0.009A(9mA)

 

But according to WEBENCH, it is shown as 0.042A(42mA).

Please refer below capture.

 

I am wondering why there is different each other.

Which should I believe?

Or on WEBENCH, is it calculated by other formula?

About inductor and output Capacitor on WEBENCH,

Is it base on above parameter?

(Peak-to-peak inductor ripple current)

 

Regards,

Tao_2199

 


  • 0
    TI__Intellectual 2360 points
    Hi Tao_2199,
    The guideline you mention, where ripple current is 30% of maximum load current (for buck regulators), is good for regulator designs that are operating near the device's full current range. It keeps the regulator in continuous conduction mode for most of its operating load range, for best transient response. However, the example design you provided is running at 10% of the LM5018's maximum load current. If the 30% guideline were followed here, it would result in a very large inductor being selected.
    For the LM5018 WEBENCH designs, the target ripple current is allowed to be proportionally larger for light load designs. When the load current is less than about 150mA, the ripple current is targeted to be up to 50mA. For very light loads (like your example), this means the circuit will be operating in discontinuous mode. See this reference: www.ti.com/.../slva057.pdf for more information about continuous vs. discontinuous operation of buck regulators.
    The output capacitor selection depends on the ripple current, as described in the LM5018 datasheet.