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TPS22912C: Behavior of enable pin

na na78
Guru 16770 points
Part Number: TPS22912C

Hi

Now we are considering the following charger system.

If the charger is connected, Li-ion battery would be charged. (Figure 1)

Then, when the charger is disconnected VOUT voltage (voltage of Li-ion) appears at VIN of TPS22912C. (Figure 2)
I believe EN would be low and VIN and VOUT should be opened. So I think it is strange TPS22912C keeps on state.

What do you think of this phenomenon?

Could you give me some advice?


BestRegards

  • 0
    TI__Genius 15710 points

    Hi na na78,

    This phenomenon is happening because VIN and EN are tied together.

    When the charger is connected, and the battery is charging, the switch is turned on and power flows from VIN to VOUT. When the charger is disconnected, the input is left floating while the output has a voltage of 3.7V. Because the ON pin is high, VIN and VOUT are connected, so VIN will follow VOUT. The two will read the same voltage, and the device will never register a voltage difference from VOUT to VIN for enabling the reverse current blocking and turning the device off. On top of that, because VIN is high, EN stays high as well and the device does not turn off.

    Cheers,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    Guru 16770 points

    Hi Alek

    Thank you for reply.

    I  understood it would be normal behavior.

    Other approach will be considered.

    By the way, I wonder if there is a load switch that switches its function by monitoring VIN (or VCC).

    BestRegards

  • 0 in reply to na na78
    TI__Genius 15710 points

    Hi na na78,

    There are no load switches in our portfolio with this capability, and I have not seen any load switches that are able to support it. Detecting an open input on the switch while it is still on and VOUT is powered is a difficult thing accomplish. Because VIN will follow VOUT, a voltage difference across the switch (from VOUT to VIN) may not always be present, so the detection of VIN being disconnected is not straightforward. 

    Thanks,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    Guru 16770 points
    Hi Alek

    Thank you for your advice.
    I will consider other effective approach, after all.


    BestRegards