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TPS7A78: a few questions on implemetation

Nicholas Carley
Expert 8185 points
Part Number: TPS7A78

We need to be able to take power in from one of 3 AC input terminals, which we diode-or together.  So the AC input would already be half-wave rectified.  Can we feed this part with an already rectified source?

What is your expectation for external filtering required to meet conducted emissions?

Do you have rough pricing for the solution cost? (based on the EVM?)

  • 0
    TI__Mastermind 29150 points

    Hi Nicholas,

    I am reviewing your question but due to the US holiday and weekend, I will need until Wednesday to provide a thought out response.

    Thanks,

    - Stephen

  • 0
    TI__Mastermind 29150 points

    Hi Nicholas,

    There are a lot of design details which can affect the exact implementation.  I think estimating a solution cost is not possible without many additional details.  I have redesigned the EVM to pass EMI testing, but this latest EVM is a mix between a reference design (to pass EMI) and an EVM (to fully evaluate the IC).  It will probably not be available for sale for a few more months.  In general the EVM should cost much more than an actual implementation, but that will vary based on customer requirements and design implementation.  The TPS7A78 design solution should cost much less and require less components than a traditional cap drop circuit using diodes and LDO's, etc. 

    Depending on your EMI requirements, you can use RC filtering or LC filtering.  The necessary filtering is usually not an issue to meet, as the dominant source of EMI is from the TPS7A78 shunting events and is relatively independent of load current.  Many customers using this device like the RC filtering as they do not want magnetics in their end product.  The series resistor can also act as a surge resistor protection (if you have surge voltage requirements), or protect the TPS7A78 from the 2A input surge abs max.

    The biggest challenge will be getting the rectified voltage to the AC+ pin (I'm assuming AC- is grounded) without exceeded any of the abs max conditions.  You would need a different circuit in front of the TPS7A78 to handle your unique conditions.

    Thanks,

    - Stephen