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Hot insertion and voltage level translation

Hi,

The design has two PCBs, one main board and one daughter card.In the daughter card we are taking VCCA voltage 2.5V from main board and VCCB voltage of 3.3V from daughter card itself.

     VCCA- main board

     VCCB - daughter card

And the output enable of the voltage level translator is controlled by a GPIO from main board.

We are using the following voltage level translators.Can you please check if the parts are suitable for the above application:

1) SN74AVC8T245RHLR

2) TXB0104PWRG4

3) SN74AVCH8T245RHLR

Is there any other aspects that we should consider for error proof hot swapping of daughter card into main board?

Regards,

Bhavya

  • Bhavya,

    This application report addresses electrical protection needs during the insertion/removal of a daughter card to/from a host system. The report also breaks down the four levels of protection that TI uses to catagorize their devices. A brief summary is below (please read the application report for full details):

    1. Level 0 (No Protection) - A device that is incapable of being inserted safely without first powering down the host power supply. Damage to the device and other components on the board are almost certain if the daughter card device and the host system are not powered down before insertion or removal.

    2. Level 1 (Partial Power Down) - Allows insertion or removal of a daughter card into a host system without interrrupting the host system power. The host system must suspend signaling during daughter-card insertion or removal. TI devices that support this feature will mention Partial Power Down Mode ('Ioff') in their datasheets.

    3. Level 2 (Hot Insertion) - Includes Level 1 support with the addition of preventing driver conflict during daughter card insertion or removal. The device will remain in the high-impedance state from a power-supply voltage of 0V up to a specified voltage. Data may be corrupted, however. TI devices that support this will mention both Partial Power Down Mode ('Ioff') and Power-Up 3-State ('PU3S') in their datasheets.

    3. Level 3 (Live Insertion) - Highest level of protection. Allows insertion or removal without limitations, restrictions, or requirements of other circuitry on system power and signaling. TI devices that support this will mention Partial Power Down Mode ('Ioff'), Power-Up 3-State ('PU3S') and BIAS VCC in their datasheets.

    Please look at your application and determine which of these Levels best descibres your application requirements.

    The translators that you mentioned support Level 1. If your application needs Level 2 or Level 3, I would recommend that you look at alternative translators (see table below), or make adjustments to your application to only require support of Level 1.

    Best Regards,
    Nirav