TPS61099: Inductance for very light load

Mathias Larsen

Part Number: TPS61099
Other Parts Discussed in Thread: AFE4405

Hi,

I need an ultra small step-up circuit from around 1.8-2.5V to 3.3V for supplying the AFE4405 Rx and Tx supply.

I expect to use the TPS610994 fixed 3.3V supply.

Operating the TPS610994 in this setup means it will be under almost no load (<0.3mA) most of the time. At 25-100Hz it will see a <10mA pulse of approximately 500us.

My question is:

Can i go for a smaller inductor than the 2.2uH recommended in the datasheet for >3V output voltage

Should i go for another device?

How much can i reduce in/output caps?

Can i do more to decrease size for my use-case, as size is of high importance.

If a similar thread exists, please point me in the right direction.

Thanks :)

over 5 years ago

0 Jasper Li over 5 years ago

TI__Mastermind 46905 points

Hi Larsen,

if the output current is only 10mA, you can reduce the output capacitor. but small output capacitor would increase the output ripple. 2.2uH inductor is acceptable. I am thinking you can apply an EVM to optimize package size of the solution with the whole system.

0 Mathias Larsen over 5 years ago in reply to Jasper Li

Prodigy 90 points

Thanks for the prompt reply :)

Can I reduce the inductance to e.g. 1uH, to get a smaller inductor, or will stability suffer?

My problem is to estimate how much I can reduce the capacitor size. From transient plots it seems that the control acts fast, so I don't seem to need to take transients that much into account, correct? At the moment, I don't expect ripple from normal operation to be a problem for the AFE4405.

EVM may be a good idea to look into :)

Thanks

0 Jasper Li over 5 years ago in reply to Mathias Larsen

TI__Mastermind 46905 points

Hi Larsen

using 1uH doesn't cause stability issue. but it may impact the efficiency.
for output capacitor, it is OK to use 10uF. but it is possible for smaller capacitor in small output current.

0 Mathias Larsen over 5 years ago in reply to Jasper Li

Prodigy 90 points

Thank you for the clarification :)

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TPS61099: Inductance for very light load