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TPS22810: TPS22810

JAMES MARR
Prodigy 60 points
Part Number: TPS22810
Other Parts Discussed in Thread: LM5060, TPS2660

I am looking for a generic load switch controller for external FETs and don's seem to find anything.  Question is, will your TPS22810 work in the attached configuration to use as a generic controller?  Some quick info, circuit will ramp up slow and need to turn off quick.  Vout of chip is tied to CT to disable internal power FET and negate its gate capacitance.  QOD of chip is tied to CT to help speed up turn-off.

Thanks,

Jim Marr

Viavi Solutions

  • 0
    TI__Genius 10855 points

    Hi Jim,

    Unfortunately, I can't see the image that you provided. Can you try reattaching it, or perhaps in a different format?

    Can you elaborate on the timing window you are trying to achieve? I would not advise connecting VOUT to CT or QOD to CT.

    1. If you need to ramp slow, simply connect a large capacitor on the CT pin to decrease the slew rate and turn-on time of the deviec
    2. If you need to turn off the device quickly, connect a larger output resistor from VOUT to QOD to enable the output to disrcharge through the QOD pin,

    Please let me know if you have any questions!

    Thanks,

    Arthur Huang


  • 0 in reply to Alpha H
    Prodigy 60 points

    See if you can see the .pdf or .docx files..TPS22810.pdfTPS22810.docx

  • 0 in reply to JAMES MARR
    TI__Genius 10855 points

    Hi Jim, 

    I can see the circuit now, thanks for attaching it.

    Unfortunately, the way you have the TPS22810 configured won't work. It looks like you're using the CT pin as an external charge pump to charge the gates of both external FETs. If you have that connected to VOUT, this will incorrectly bias some of the internal circuitry. VOUT would need to be kept floating in this case. 

    If you're looking for a FET controller I recommend taking a look at the LM5060. Page 26 of the datasheet contains an example circuit using back-to-back FETs. You could also take a look at the TPS2660 if you're looking for an integrated solution with B2B FETs.

    Out of curiosity, what is the application behind this design? If you're looking for a slower turn-on for the external FETs, I believe the diode should be facing the opposite direction to allow for the capacitor to charge up through the resistor, and then quickly discharge through QOD as the TPS22810 is disabled. 

    Thanks,

    Arthur Huang


  • 0 in reply to Alpha H
    Prodigy 60 points
    Arthur,
    Thanks for the help! I realize you cannot connect Vout to CT because the intrinsic diode of the pass FET would kill gate voltage which is all immaterial anyway because it turns out that the CT pin is NOT the gate drive of the internal FET, it looks like ground so you cannot use external FET's at all because you can't get to the charge pump voltage. The LM5060 would work but is too big and expensive! The TPS2660 besides being too big and expensive is only good for 2A, we need 5A. Which brings us to the TPS259270, very close but needs a little bigger pass FET with less resistance to keep power dissipation down. (dissipates 700mW @ 5A) I may try it next and use the BFET output to drive my external FET's! The application is to power a couple of TPS64500 PMIC chips. The switch is to ramp up the output, since we have quite a bit of bulk capacitance on the output and turn off extremely fast in case the battery turns off (LIion), as to not have anyone else discharge our capacitors while we do a quick controlled sequenced power down.