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TPS7H5005-SEP: Error Amplifier Saturation Characteristics

David Matia
Prodigy 40 points

Part Number: TPS7H5005-SEP

Tool/software:

Hello,

I'm considering applying my own soft start mechanism with the TPS7H500x family of parts.  I would add a summing junction to the inverting input of the error amplifier and sum the feedback voltage and a voltage slightly higher than the 0.613 V internal reference .  With the soft start pin already high, this summed voltage is intended to still hold off the power supply, and in this way the synchronous rectifiers will have the opportunity to be active during wake-up.  However, the error amplifier will essentially be open loop. 

What will happen when the amplifier is saturated at it's low rail, and how well will it recover from that state when I pull down that summed voltage and wake up the power supply?

  • 0
    TI__Mastermind 29705 points

    Hey David,

    Generally to get around the issue of the synchronous rectifiers not being on, we look to our family of drivers TPS7H60X5-SEP.
    The drivers themselves can generate the synchronous rectification signal during start up.

    As far as your plan, what you described may work, but the details would depend on how exactly you implement it.
    It would likely not be a monotonic soft start just due to how the feedback loop would try and act.

    Thanks,
    Daniel

  • 0 in reply to Daniel Hartung
    Prodigy 40 points

    Should I expect the opamp to draw a lot of power in saturation, take a long time to recover from saturation, etc.?

  • 0 in reply to David Matia
    TI__Mastermind 29705 points

    Hey David,

    The op amp current draw should be on the order of 100-190 uA as per the electrical specification.

    The time it would take to recover would be determined by the control loop.
    Whether or not that is a long time is somewhat up to the design.

    Thanks,
    Daniel