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LM2623: start up voltage

KANJI SHIBATANI
Mastermind 6205 points
Part Number: LM2623
Other Parts Discussed in Thread: TPS61021A

Hello

My customer is finding out the boost converter solution (FY18 portable medical)  for:

Vin=0.9~1.5V  (Alkaline x 1)

Vout=1.8V   Io>0.1A~

One candidate is LM2623 , but  I have two concerns.

*1 This need start up voltage  >1.1V

*2  Vin=Vout 

( For this, it will be Okay because of another post.)

http://e2e.ti.com/support/power_management/simple_switcher/f/858/p/511789/1858892?tisearch=e2e-sitesearch&keymatch=lm2623#1858892

 

Q1  Do you think LM2623 is Okay for this project?

Q2  I think  using TPS61021A ( Vout=1.8V) and LDO is better solution, but how do you think?

 

Please advice your opinion

Best Regards

 

 

 

 

 

 

 

 

  • 0
    TI__Guru 68495 points
    if you VIN can be 0.9VIN, the LM2623 cannot startup. You should consider the TPS61xxx part. The TPS61021 can be directly programmed to 1.8VOUT. Please use our online tool Webench to help design.
  • 0
    TI__Mastermind 21720 points
    Kanji,

    With the input voltage range that you specify the LM2623 might not be the best selection for this application. As you note the LM2623 needs greater than 1.1V to start-up. So for some points of operation the IC might not start up correctly because the input voltage can be below the minimum start-up voltage.

    As you mention the TPS61021A might be a better solution for the application. It has a lower start-up voltage and has pass-through operation as described in section 7.3.5 of the datasheet. Also since the TPS61021A is a synchronous converter the efficiency should be greater than the LM2623. With this solution an LDO is not needed, the output voltage can just be set to 1.8V by adjusting the feedback resistors.

    Thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Mastermind 6205 points

    Dear Garret san,

    Thank you for your answer immediately.

    I am sorry my TYPO that  Vout =1.5V/0.1A  ( Vin=0.9V ~ 1.5V), NOT Vout=1.8V.

    ( LM2623  Vout(min) is 1.24V , but  start up is 1.1V)

    (TPS61021A Vout(min) is 1.8V)

    As per your recommend,  I will suggest customer to select TPS61021A  + TLV73315P.  

    If you have any another opinion, please give me your opinion.

    Thank you again

    Best Regards