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TPS65217: Can't restart normally after voltage drop

Yishan Chen
Intellectual 1440 points
Part Number: TPS65217
Other Parts Discussed in Thread: TPS65126, TPS65216

Hi,

Customer use TPS65217 as the power supply for AM335X.

And they connect 5V voltage source to supply the TPS65217. Besides, they add a super capacitor to extend the supply.

They found if they pull out the 5V power supply and use super capacitor to power the TPS65217.

When the voltage is drop under 3.8V and plug-in the 5V voltage source, TPS65127 can restart normally.

But if the voltage is larger than 3.8V and plug-in the 5V voltage source, TPS65127 can't restart normally.

What is the reason behind this? How do wo solve that? Thank you.

Yishan Chen

  • 0
    TI__Mastermind 20960 points

    Hi Yishan,

    • Which supply is the 5V connected to? USB or AC?
       
    • Where is the super capacitor connected? Is it connected at the BAT pin input?
       
    • Can you share a schematic for reference? If you need a private space to share I can set one up.
       
    • Do you have any scope shots that show the issue you are seeing more clearly?
       

    If the TPS65217 PMIC hasn't experienced a full UVLO condition (full loss of all supply voltages to reset the digital core) and is still operating in ACTIVE state due to the super capacitor keeping the system alive, you will need to hold the push button down for >8 seconds to initiate a RESET, as shown by the state diagram from the datasheet below:

    If you don't want to use the push button, your other option for a full reset would be to either pull PWR_EN low or power cycle the input supply which would require that the super cap be below the operating input voltage. If the super cap is still keeping the system in ACTIVE state, reapplying the 5V input won't cause a reset, it will only switch the input source from the super cap to the 5V input and continue in ACTIVE state.

    Regards,

    James

  • 0 in reply to James Steenbock
    TI__Intellectual 1440 points

    Hi James,

    I can show you the schematic, please create a private space for us.

    5V Input and super capacitor is all connected in AC Pin.

    Sorry that I don't have much scope shots for you but I think the phenomenon is very clear.

    Do we have other solution to reset the devices? Customer can't push the bottom or pull down PWR_EN Pin.

    If they switch to TPS65126 with separate input inside the chip, could this solve customer question?

    Yishan Chen

  • 0 in reply to Yishan Chen
    TI__Mastermind 20960 points

    Hi Yishan,

    The only other way to reset the chip is to drop the input voltage low enough so that the digital core is reset. This would mean that your reset timing is dependent on how long it takes the super capacitor to discharge. If you had some sort of active discharge through a resistor this time could be reduced.

    Yishan Chen said:
    If they switch to TPS65126 with separate input inside the chip, could this solve customer question?

    Just to be clear, do you mean the TPS65216 in the statement above? If so, I'm not entirely sure if this device will solve the issue you are seeing. The TPS65216 will behave the same way. If you do not reduce the input voltage below the threshold to trigger a UVLO condition the IC will continue to operate unless a direct reset signal is given to the PMIC through the Push Button.

    The only way to cause a reset from an input voltage drop is to go below the UVLO threshold and trigger a reset event.

    Regards,

    James