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TPS650861: 5V Application & VSYS Sequencing Requirement

Don Schelle
Expert 4150 points
Part Number: TPS650861
Other Parts Discussed in Thread: , LM2767, TPS61040, LM2665

Hello,

With regards to the TPS650861 in a 5V input requirement.   We understand that a boost converter is required to generate the 5.8V VSYS rail.   Is there any particular part that's recommended for this?

Regarding the 5V & 5.8V rails.   Is there any required sequencing?   And is the diode OR circuit shown in 6.7 required?  I think we'd prefer to leave this out and connect the output of the 5.8V boost directly to VSYS.

Don

  • 0
    TI__Genius 17380 points

    Hi Don,

    We've seen a few different boosts used before. We use TPS61040 on the BOOSTXL-TPS650861 board which I like as far as a converter goes. LM2665 is also popular for smaller component count. LM2767 is I think the cheapest I've seen someone use but it appeared to barely handle the peak current during start-up so I generally recommend a slightly higher current capability if using a charge pump.

    As far as sequencing, the requirement is that V5ANA - VSYS should not exceed our internal FET body diode voltage, roughly 0.5V or else current can flow from V5ANA into VSYS pin in an unplanned manner. The diode OR circuit is generally not required, most boost converters / charge pumps have a built in diode and so they support output = input during ramp up. I would avoid any "True Isolation" type boost converters.

    Let us know if you have any more questions.