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TPS63070: Very wide input range buck-boost

Mark Sheffield1
Prodigy 40 points
Part Number: TPS63070
Other Parts Discussed in Thread: , TPS61202EVM-179, TPS61202, TPS63060, LM2623

Hey everyone - I am looking for a wide input range buck/boost (or boost/buck) that will work from 2V (3V minus 3 diode drops, or roughly 2V, give or take) to 10V. The three diode drops come from an Intrinsic Safety/ATEX requirement. The output is at 5V, current is roughly 300mA into a mostly resistive load. I have tested the EVM for TPS63070 (TPS630702EVM) which is very close to what I need. High end is great and it works well and even will work down to 2V in, but won’t start up at that low a voltage b/c of the positive-going hysteresis – 850mV (yikes!).

I also tested TPS61202 (TPS61202EVM-179) as a boost that can work all the way down below 2V and will start up at approx. 2.1V, that tells me that it’s possible to do. The top end is low, 5.5V, so I can’t use this as a real design choice here.

Do you have any ideas to try that will stretch the startup range of the TPS62070 down to 2V? Can the hysteresis be decreased in any way? The only other solution is a boost (non-synchronous) followed by a buck, but this is really a pretty ugly solution.

Thoughts?  thanks - Mark

  • 0
    TI__Expert 7925 points

    Hi Mark,

    I couldn't find any TI buck-boost converter that can start so low. The TPS63070 can go down to Vi=2 V, but need 3 V for start-up. The TPS63060 can start at 2.5 V, but cannot go lower. 

    Is there anything else after the 3 diodes except for the converter? If there is no other load, and the converter is disabled, you might be able to charge the input capacitor to 3 V via diodes, if the current is low enough.

    Otherwise, you could cascade boost and buck. There are a few boost converters that can start below 2 V, such as the LM2623. You could set it to generate 12 V, and then step it down with any 12 V to 5 V buck converter.

    Best regards,
    Milos 

  • 0 in reply to Milos
    Prodigy 40 points

    Hi Milos - thanks for the reply, those are exactly my findings as well, all the way down to using the 2623 to boost and follow with a buck - I even have the EVM for the 2623 on my desk and will be testing that configuration soon.  It's a bit ugly but it seems to be the only thing that holds together spec-wise.

    rgds - Mark

  • 0 in reply to Mark Sheffield1
    TI__Expert 7925 points

    Hi Mark,

    I tested the TPS63070 with 3 schottky diodes on the input side, and even though the input voltage charges up to 3 V when the converter is disabled, the startup is not possible. Likely due to inrush current causing voltage drop on diodes and triggering the UVLO.

    It seems that cascading boost and buck is the only options for these specifications.

    Best regards,
    Milos


  • 0 in reply to Milos
    Prodigy 40 points

    Hi Milos - thanks for checking.  I'll be back in touch if I run into anything with the 2623 solution

    best rgds - Mark

  • 0 in reply to Mark Sheffield1
    TI__Expert 7925 points

    Hi Mark,

    Then I will close this thread. The LM2623 is covered by another product line, and if you have any questions feel free to open a new thread.

    Thanks and regards,
    Milos