TPS61040: Minimum switching freqency

Yogesh Nadarge

Prodigy 110 points

Part Number: TPS61040

Tool/software:

Hi,

I'm planning to use TPS61040 for my below requirement:

These are the inputs I've given to Webench.

VIn(Min)= 4.8V

VIN(Max) = 5.5V

Vout=7V

Iout(Max) =50 mA but typical would be very small around 10mA.

When I tried to take design from TI Webench, it is giving me very high value of inductor which 22uH. Is it possible to use low inductor values such as 6-10uH.

Also what is the minimum switching frequency of TPS61040.

Thanks,

Yogesh

11 months ago

0 Lei Zhong 11 months ago

TI__Mastermind 18980 points

Hi Yogesh,

It's OK to use a inductor with smaller inductance such as 6-10μH.

TPS61040 uses hysteresis control, not fixed frequency or COT control. So it's frequency is hard to calculate when load is very light, such as 10mA. It may switching several cycles in frequency around hundreds of kHz, and then stop for a long time. You may verify the frequency on EVM if it's critical in your application.

Regards

Lei

0 Yogesh Nadarge 11 months ago in reply to Lei Zhong

Prodigy 110 points

Hi Lei,

Thanks for the response!

But when I try to calculate the Inductor value using the formula given in the SLVA372D considering the ripple current of 30% then the I'm getting an inductance of 66.59uH which is beyond the recommended value. Considered the Fs=1MHZ.

0 Lei Zhong 11 months ago in reply to Yogesh Nadarge

TI__Mastermind 18980 points

Hi Yogesh,

The formula you used should be for continuous mode or PWM mode.

In you application the device works in DCM mode. It's OK to use a inductor with smaller inductance such as 6-10μH.

Regards

Lei

0 Yogesh Nadarge 11 months ago in reply to Lei Zhong

Prodigy 110 points

Hi Lei,

Thanks!

Could you please share the value of load current above which TPS61040 works in continuous mode? or it works in DCM mode only?

Best Regards,

Yogesh N

0 Lei Zhong 11 months ago in reply to Yogesh Nadarge

TI__Mastermind 18980 points

Hi Yogesh,

I attached a simple calculator for your reference.

0268.Calculator.xlsx

Regards

Lei

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TPS61040: Minimum switching freqency