LMR14030: Switching frequency in DCM mode

na na78

Part Number: LMR14030

By setting RT, switching frequency would be set.

LMR14030 can have three operation mode, CCM, DCM and sleep.

Is Fsw changed depending on operation mode?

1.
For example,
When RT = 11.5Kohm, switching frequency is set as 2MHz. However, actual swiching frequency would be decreased if load is light in DCM?

2.
What about the situlation of sleep mode?

BestRegards

over 8 years ago

0 Vental Mao over 8 years ago

TI__Expert 5745 points

1,Yes, you are right. But LMR14030 is a non-synchronize converter, it also will be into DCM without decreasing frequency when the Iout>300mA(300mA is the sleep-mode current threshold) in some conditions.
2, When the Iout<300mA, it will be into sleep-mode, also the DCM, and frequecny will be decreased.

0 na na78 over 8 years ago in reply to Vental Mao

Guru 16770 points

Hi Vental

Thank you for your reply.

So, is the operation of LMR14030 in sleep mode like PSM?

> it also will be into DCM without decreasing frequency
>when the Iout>300mA(300mA is the sleep-mode current threshold) in some conditions.
Do you mean the situation like Figure 25 (DCM) and Figure 26 (CCM) of the datasheet?
Because they seems to be same switching frequency.

BestRegards

0 Vental Mao over 8 years ago in reply to na na78

TI__Expert 5745 points

Yes, you are right.

0 na na78 over 8 years ago in reply to Vental Mao

Guru 16770 points

Hi Vental

Thank you for your reply.

Finally, please make me question about sleep mode.

The figure 25 shows DCM mode of LMR14030.

As the reason why it does not go into sleep mode, the circled peak at the end of switching is not below the current threshold of 300mA.

Is my understanding correct?

BestRegards

0 Vental Mao over 8 years ago in reply to na na78

TI__Expert 5745 points

Yes, you are right.
If the output voltage is within regulation and the peak switch current at the end of any switching cycle is below the current threshold of 300 mA, the device enters Sleep-mode.

0 na na78 over 8 years ago in reply to Vental Mao

Guru 16770 points

Hi Vental

Thank you for reply.

I understood.

BestRegards

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LMR14030: Switching frequency in DCM mode