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TPS22994: Is the state maintained at the output of the load switch when the switch is disabled?

Bogdan Antonescu
Prodigy 30 points
Part Number: TPS22994

Hello,

I would be grateful for some answers if anybody has experience in designing with the TPS22994 power load switch.  It is a quad channel load switch that contains a special function (SwitchALL) that allows multiple devices to be enabled or disabled synchronously via a single I2C command.

We are NOT interested in using that feature as described, but I have a question related to this feature.  Is it safe to assume that once I disable the switch, the last state of its outputs is maintained? In other words, I need to know that the switch keeps its last VOUT state once I disable the switch.

By the way, does disabling the switch mean disabling the I2C communication?

I am asking that because I want to close a switch (we use only one out of the four switches/channels) and then to power down VDD=3.3V (for the I2C bus).  The VBIAS is still active and hooked to a battery circuit.  I need to keep that "closed" state for the only ONE switch I use while VDD is zero.  Can I count on the output state being maintained?  I already have an ST Micro part that does that, but its operational temperature range is only 0 to 70C, so the TI part is better with that respect.

What do I do with ONx pin/input while I have Switch x or the entire load switch disabled with respect to I2C communication? Can I still have it connected to VINx like in Fig 55, in Section 10.2.2 (page 31 of the spec sheet)? I assume, yes.

Last question: can I use 2.5V for VBIAS? I know the spec sheet says min. 2.7V, but my battery voltage gets regulated down to 2.5V.  It is a circuit that takes either main power or battery power, and the result gets regulated to 2.5V.  This is what use for VBIAS.  We could probably change the LDO to 2.7 or 3V, but it would be much easier to use 2.5V for VBIAS (if possible).

Thank you so much for your help!

Bogdan

  • 0
    TI__Genius 10652 points

    Hi Bogdan,

    Could you please clarify what you mean about the "last state of the outputs"? 

    Bogdan Antonescu said:
    We are NOT interested in using that feature as described, but I have a question related to this feature.  Is it safe to assume that once I disable the switch, the last state of its outputs is maintained? In other words, I need to know that the switch keeps its last VOUT state once I disable the switch.

    I think you mean about the configuration by I2C, such as When you disable the each switch  (ONx driven high/low or by writing to the correct addresses mentioned in section 10.1.6), it just pulls the internal powerfet gates down, it doesn't clear the registers, so the configuration will be maintained. 

    Registers will be cleared when VBIAS drops out though, so VBIAS needs to be maintained. 

    Bogdan Antonescu said:
    By the way, does disabling the switch mean disabling the I2C communication?

    Turning off power switches does not mean I2C communication is disabled or interrupted, you will still ahve access to the registers. 

    You can disable / enable each switch by driving ONx pins, or alternatively you can tie ONx to VINx and control each switch by I2C, as detailed in 10.1.6

    Bogdan Antonescu said:

    I am asking that because I want to close a switch (we use only one out of the four switches/channels) and then to power down VDD=3.3V (for the I2C bus).  The VBIAS is still active and hooked to a battery circuit.  I need to keep that "closed" state for the only ONE switch I use while VDD is zero.  Can I count on the output state being maintained?  I already have an ST Micro part that does that, but its operational temperature range is only 0 to 70C, so the TI part is better with that respect.

    The register data will be maintained as long as you have VBIAS present, so you are good in this respect. 

    Bogdan Antonescu said:
    What do I do with ONx pin/input while I have Switch x or the entire load switch disabled with respect to I2C communication? Can I still have it connected to VINx like in Fig 55, in Section 10.2.2 (page 31 of the spec sheet)? I assume, yes.

    Yes you can tie ONx to VINx if you plan to use exclusively I2C to turn on /off each switch.

    Bogdan Antonescu said:
    Last question: can I use 2.5V for VBIAS? I know the spec sheet says min. 2.7V, but my battery voltage gets regulated down to 2.5V.  It is a circuit that takes either main power or battery power, and the result gets regulated to 2.5V.  This is what use for VBIAS.  We could probably change the LDO to 2.7 or 3V, but it would be much easier to use 2.5V for VBIAS (if possible).

    You can try this and probably will work but we only guarantee the specs / performance when you use the device withint the recommended operating range.

    Please let me know if any further questions, and if this answered all your questions bplease let me know by pressing the green button.

    best

    dimitri