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TPS61094: Automatic Buck or Boost Function without supercap

Quirin Hauf
Prodigy 550 points
Part Number: TPS61094

Tool/software:

Dear Experts, 

I am using this switch regulator in a battery-operated product. I have implemented the regulator as described in Figure 8-1 of the datasheet. In Figure 8-1, an output voltage of 3.6 V is specified for an input voltage range of 2.7-4.3 V. Based on this, I assumed that the regulator would switch to buck mode when the input voltage is higher than the set output voltage.

Unfortunately, this is not the case in my circuit. The switch regulator goes into bypass mode, and the output voltage directly rises with the input voltage, exceeding my set 3.3 V.

I suspect I have misinterpreted the datasheet. Is it nonetheless possible to operate the switch regulator in buck mode?

I would like to set up the application without the supercap. Is this technically possible?

Thank you in advance.

Regards 

  • 0
    TI__Expert 8835 points

    Hi Quirin,

    Yes, there some misunderstanding here. TPS61094 is a bi-directional converter and its buck mode charges vsup, not to vout.

    best regards,

    travis

  • 0 in reply to Travis Wang
    Prodigy 20 points

    Thanks Travis for your quick answer!

    Makes sense, I was assuming this as well now after validating a prototype. However, when looking at Figure 8-1 and Table 8-1 in the Datasheet Vout is specified as 3.6 V at an input voltage of 2.7-4.3 V. I find this misleading as it would imply that the device somehow limits the output voltage to 3.6 V. But in fact it will rise up to Vin (4.3 V). Depending on the logic in the switching regulator such a limiting behavior could at least theoretically been possible. Maybe those points could be rephrased in the datasheet to make this clear to the user?

  • 0 in reply to Jonas Remmert
    TI__Mastermind 18970 points

    Hi Jonas,

    Figure 8-1 and Table 8-1 is a general application example, in which the TPS61094 is configured as an boost with by-pass function, and the Vout target is 3.6V. When the Vin is higher than the Vout, the by-pass function works so the Vout follows the Vin and higher than the Vout target.

    Boost converter with by-pass function always work in this way. So there should be no confusions.

    Regards

    Lei

  • 0 in reply to Lei Zhong
    Prodigy 20 points

    Hi Lei,

    thanks for the clarification! Somehow, I got confused with the mentioned buck mode at several places in the datasheet. But I understand now that this is only relevant for the charging voltage, not for Vout.

    Regards,

    Jonas

  • 0 in reply to Jonas Remmert
    TI__Mastermind 18970 points

    Hi Jonas,

    You are correct. 

    The buck mode only for supercap charge, not for the Vout.

    The Vout is either by-passed from the Vin, or boosted from the supercap.

    Regards

    Lei