TPS74901: When input=3.8V and output 3.3V, how to configure TPS74901 Vbias?

Eggsy Pang

Expert 4985 points

Part Number: TPS74901

Hi team,

My customer use our LDO TPS74901 to realize the input=3.8V and output 3.3V/2A. Attached file is SCH.

I am not sure how to configure TPS74901 Vbias. It said Vbias need >1.75+ Vout in the datasheet.

Could you help me review the SCH and how to change?

Thanks!

01-POW.pdf

over 4 years ago

0 Kyle Van Renterghem over 4 years ago

TI__Genius 13095 points

Hi Eggsy,

With Vout=3.3V, Vbias cannot be tied to a Vin voltage of only 3.8V. If the output current will never be above 2A then I'd recommend Vbias be at least 1.64V above Vout which would mean tying it to 4.94V or higher (this was determined using figure 8 and then using the same amount of margin for 2A as there is between the typical char graph at 3A and the EC table max value). If you are going to have any events more than 2A then I'd recommend using the max value listed in the EC table, which is Vout+1.75V (Vbias=5.05V).

0 Eggsy Pang over 4 years ago in reply to Kyle Van Renterghem

TI__Expert 4985 points

Hi Kyle,

Thanks for your help!

So can it use 5V producted by DCDC in SCH?

Would it add noise to LDO due to DCDC?

Thanks!

0 Kyle Van Renterghem over 4 years ago in reply to Eggsy Pang

TI__Genius 13095 points

Hi Eggsy,

Yes, many of our LDOs are used in systems where they are powered by a switching regulator so there shouldn't be any issue. The output noise of the LDO may be slightly higher, but the incoming noise will be attenuated by the Vbias PSRR, I've included the graph from the datasheet showing the how much attenuation you can expect to get from this device.

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TPS74901: When input=3.8V and output 3.3V, how to configure TPS74901 Vbias?