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Original question:

TPS61322: TPS613221A: Vin > Vout

TPS61322: Vin greater than Vout

Jason Cutler
Prodigy 40 points
Part Number: TPS61322
Other Parts Discussed in Thread: TPS63802, TPS61099

Hi,

The datasheet for the TPS61322 series lists Vin as 0.9 to 5.5v; higher than the Vout values for most of the model range.

What is the operation in this situation? Will a 3.3V Vout model (TPS613221A) passthrough Vin to 5.5V and start boosting when it drops below 3.3V?

My specific scenario is the possibility of a 3.6V lithium battery in an existing TPS613221A circuit that requires 3.1 to 4.2 Vout volt range.

Thankyou.

  • 0
    TI__Mastermind 21565 points

    Hi Jason:

    The Vout can't regulate well with a basic boost converter. If the output voltage drops below the input voltage, the inductor current will be clamped by the DCR of the inductor and the on resistance (Rds,on) of the high side MOSFET.

    May I know what's your requirement for such situation? We have TPS61099, which can help to regulate the Vout even Vin is little larger. otherwise you may need to choose a buck-boost converter, such as TPS63802. 

  • 0 in reply to Minqiu Xie
    Prodigy 40 points

    Hi Minqiu, thanks for your quick reply.

    Minqiu Xie said:
    If the output voltage drops below the input voltage, the inductor current will be clamped by the DCR of the inductor and the on resistance (Rds,on) of the high side MOSFET.

    Could you explain what this means? This is my first prototype and have much to learn.

    Basically I was looking for low quiescent current in a package I could hand solder so I avoided QFNs.

    I've had practice now so the TPS63802 looks like exactly what I need for my next revision.

    For my two current prototypes with the TPS613221A, the batteries I was looking at using are 3.2-3.3V (3V nominal) or possibly a higher temp rated 3.6V model.

    Max current draw at 3.3V is about 20mA.

    I don't need buck regulation; just what the Vin range on the datasheet means to operation above Vout.

    Thanks

  • 0 in reply to Jason Cutler
    TI__Mastermind 21565 points

    Hi Jason:

    So what do you expert for once Vin is higher than Vout?

    If you want to regulate  the Vout even Vin is a little high, I will recommend TPS61099, as it has down mode function. Details could be checked in datasheet.

  • 0 in reply to Minqiu Xie
    Prodigy 40 points

    Hi Minqiu,

    Minqiu Xie said:
    So what do you expert for once Vin is higher than Vout?

    My thought from the datasheet's max Vin of 5.5V that maybe the unit would just pass through any voltage over Vout...no regulation.

    I don't require regulation down to 3.3V, just wanted to know if 3.7Vin or so would damage the regulator.

    Thanks

  • 0 in reply to Jason Cutler
    TI__Mastermind 21565 points

    Hi Jason:

    THe max Vin means, it's not recommend the Vin exceed this value, otherwise the device may damage or mis-operation.. 

    If Vin=3.7V, it won't damage the boost converter. But the Vout can't regulate to 3.3V. If you don't have such requirement, it's OK.

  • 0 in reply to Minqiu Xie
    Prodigy 40 points

    Minqiu Xie said:
    If Vin=3.7V, it won't damage the boost converter. But the Vout can't regulate to 3.3V. If you don't have such requirement, it's OK.

    Perfect!

    Thanks very much Minqiu.

  • 0 in reply to Jason Cutler
    TI__Mastermind 21565 points

    Hi Jason

    Welcome~ It's my pleasure to support.