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Disconnect slave device from I2C bus after power down

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Replies: 9

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Hi,

I want to power a slave device from the secondary LDO output of a PMIC. Host is connected to primary output of PMIC. This slave device is i2c controlled and hence on the main i2c bus of the host. Can you suggest part to disconnect the slave device from main i2c bus to prevent back power and disruption of i2c line when the LDO is turned off(slave device is not getting power but it's i2c lines remain on the main bus). To avoid level shifting, the voltage levels on main output and LDO output are same. Thanks!

  • Hi Mir,

    Thanks for reaching out!

    Please look at TPS25200 and check whether it meets your requirement.

    Best Regards,

    Rakesh

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    To find the latest information on Power Switches, Visit www.ti.com/powerswitch 

  • In reply to Rakesh:

    Hi Rakesh - This part looks like power switch. I need to disconnect device from i2c bus i.e.,  I would like to disconnect the SCL/SDA lines after LDO power cutoff. Thanks.

  • In reply to agusta mir:

    Hi Mir,

    understood. I am diverting this post to Analog switches products to suggest right solution for you.

    http://www.ti.com/switches-multiplexers/analog/products.html

    Best Regards, Rakesh

    --------------------------------------------------------------------------------------------------------

    To find the latest information on Power Switches, Visit www.ti.com/powerswitch 

  • Use any two-channel SPST switch that supports the desired voltage; e.g., SN74LVC2G66.

  • In reply to Clemens Ladisch:

    Hi Mir,

    Additionally - the powered-off protection feature will help ensure the system doesn't back power as you mentioned. Here is a link to a tech note on the subject http://www.ti.com/lit/an/scda015b/scda015b.pdf

    Here is the TI selection table sorted on 1:1 SPST devices with at least 2 channels. What do you think of the TMUX1511? This device has 4 channels but is optimized for low capacitance and has low leakage in powered off state. You can connect the unconnected pins to GND if not needed.

    Othewise you can use a device like the TS5A23166.

    Regards,

    Dakotah

  • In reply to Dakotah:

    Thanks for the notes, that is valuable information! How would the SN74LVC2G66 (previously recommended) differ from TMUX136 or TS5A23166 ? 

  • In reply to agusta mir:

    Hi Agusta,

    The SN74LVC2G66 device does not have powered-off protection. While the other devices do.

    It comes down to the architecture of if the switch will also be powered from the PMIC output and turned off or if it will be on the supply of the main system.

    Regards,

    Dakotah

  • In reply to Dakotah:

    Hi Dakotah, Just trying to clarify the latter half of your statement - If the switch is also powered from the same controllable PMIC output, will the behavior of the SN74xx device be similar as TSAxx device. the price difference is almost 2x for similar package, so I'm interested in knowing the best possible device for same functionality.

  • In reply to agusta mir:

    If the switch itself is powered all the time, then you do not need powered-off protection. If the I²C pull-up resistors and the switch are using the same supply (as in your case), or if the switch is powered up first, then you are safe.