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TPS7A20: Input Voltage Margin Considerations for TPS7A2055PDBVR with Buck Regulator

Bjornar Syverstad
Prodigy 40 points
Part Number: TPS7A20

Tool/software:

I am considering using the LDO TPS7A2055PDBVR. According to the datasheet, the recommended maximum input voltage is 6.0 V, and the absolute maximum rating is 6.5 V. The LDO will be powered by a buck regulator, which typically introduces some overshoot and undershoot during transients.

In this type of application, is it acceptable to set the nominal output of the buck regulator to 6.0 V and allow transient deviations that stay below 6.5 V? Or would it be better to set the buck regulator output to around 5.75 V to ensure that any overshoot stays below the 6.0 V recommended maximum?

What is considered best practice in this kind of design?

  • 0
    TI__Expert 5520 points

    Hi Bjornar,

    Anywhere between 6.0V-6.5V won't damage the part but also won't be guaranteed to have performance within the spec limits in the EC table. But as most of the characteristics don't exhibit a high level of VIN dependence, you shouldn't expect much performance degradation in that range anyways.

    However, I'd usually recommend to just set the buck regulator at the lower voltage, as you get more predictable performance and improved overall efficiency (most of the voltage step happens in the significantly more efficient buck converter). 

    Since the OPN has 5.5Vout and a 0.145VDO limit, beware that any input below 5.645Vin may bring the device into dropout (where it will not be able to reach the regulated output voltage). To note, VDO is load dependent and you can technically scale back that limit with stricter operating conditions:

    Your priorities should be in this order:

    1. Below AMR (VIN<6.5V)

           Consequence: Possible part damage

    2. Above Dropout Limit, VIN>VOUT+VDO_max (VIN>5.645)

           Consequence: Device output will not fully regulate

    3. Within recommended operating conditions (VIN<6.0V) 

           Consequence: Possible out of spec performance 

    The best thing is to lower buck converter nominal output as much as possible while guaranteeing it will stay above the dropout limit, but 6.0V should be fine for your application.

    Best,

    Gregory Thompson