LMR14006: Minimum on time calculation in DCM mode

vaibhav waman

Part Number: LMR14006

Hello,

In light load condition LMR14006 enters into DCM mode. It has minimum on time period of 95ns.

I am using at 12V input to 5V output configuration. What formula I should use to calculate minimum on time in DCM mode ?

From this I want to verify in my application output voltage will not rise above 5V due to given minimum on time mentioned.

Thank you.

Best Regards,

Vaibhav Waman

over 2 years ago

0 Youhao Xi over 2 years ago

TI__Guru* 79475 points

Hello Vaibhav,

For the buck converter, the DCM duty cycle is dependent on the load. Specifically,

where

t1 is the on time
Iout the load current
L1 the buck inductor's inductance
Vout the output voltage
Vf the rectifier diode forward voltage drop,
Vin the input voltage
Fswitch the switching frequency.

If the calculated t1 is shorter than the min on time, you should consider to add a dummy load prevent the Vout from rising above the regulation level.

Wish this helps.

Thanks,

Youhao

0 vaibhav waman over 2 years ago in reply to Youhao Xi

Intellectual 320 points

Hello,

In this formula if I consider scenario of light load that is Iout is very small in that case only I can see need of external dummy load ? am I correct or Iout should always be maximum output current ?

0 Youhao Xi over 2 years ago in reply to vaibhav waman

TI__Guru* 79475 points

Hello Vaibhav,

Iout in the equation is the small light load which causes the IC running into DCM. At your max output current, your circuit should be designed to operate in CCM and the duty cycle is determined by (Vo+Vf)/Vin.

Thanks,

Youhao

0 Youhao Xi over 2 years ago in reply to Youhao Xi

TI__Guru* 79475 points

Hi Vaibhav,

May I assume the issue is resolved so I can close the thread here? You are welcome to re-open it by adding a new post.

Thanks,

Youhao

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LMR14006: Minimum on time calculation in DCM mode