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LSF0102: Can LSF0102 support hot swap

Sunny Qin
Expert 4890 points
Part Number: LSF0102

Hi Team,

My customer design an daughter board, which use our LSF0102 as interface with mother board, can Can LSF0102 support hot swap? that means can they plug in the daughter board when mother board is power on?

if not, do you have any recommendation to do the hot swap?

Thanks.

Regards, Sunny

  • 0
    TI__Guru* 97046 points

    Hi Sunny,

    If the bus connects properly (first ground, then vcc, then data), the LSF0102 won't be damaged by hot swapping, however that's not the whole story.

    I would not recommend to use the LSF0102 as an interface to a motherboard, primarily because the device is passive and won't redrive any signals. Busses typically have long traces with high parasitic capcitance, which will slow down the LSF very greatly. There's a video series that discusses this here: Understanding the LSF family of bidirectional, multi-voltage level translators

    To make a long story short - if the bus is actively communicating while you add a new device and you want to prevent adding errors, then you need a device with the "Bias Vcc" feature. This is an extra supply pin that pre-charges the outputs of a new device as it's connected to the bus, which prevents errors.

    There's an application report on this topic here: Logic in Live-Insertion Applications

    There aren't very many parts in our portfolio with the Bias Vcc feature -- they can all be seen here: Bias Vcc Parametric Search

  • 0 in reply to Emrys Maier
    TI__Expert 4890 points

    Hi Emrys,

    Really thanks for your comments, checked with customer, they do not care data error when plug in, but only care if it`s safety for LSF0102. As the connector are general ones(all pin are the same length), so they can not guarantee first ground, then vcc, then data, all these pins should connect to mother board at the same time. Is there any risk for LSF0102?

    Regards, Sunny 

  • 0 in reply to Sunny Qin
    TI__Guru* 97046 points

    Hi Sunny,

    Yes, if there is no way to know which pins are connected first, then it's also impossible to know what will happen to the device.

    Boards that are not connected can have wildly different ground potentials on them -- they will only be the same after the grounds have been shorted together.

    All hot-swap systems should be designed to have longer GND and Vcc pins so they connect first -- most will have the GND pin be the longest, with Vcc next, then bias Vcc, and finally the data ports.