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TPS7A57: Generation of 5V out from 5.5V input without any additional input/bias voltages

Bivin George
Expert 1027 points
Part Number: TPS7A57

Hi

Please refer the image below.

I need to generate 5V from 5.5V supply, but above is not generating the same. It is found that bias pin requires minimum of 8V input to generate the same.

If i'm operating the same in charge pump mode by connecting it to 5.5V supply, will the above circuit generate 5V or will it be in disabled form due to the minimum threshold requirement for Bias pin.

Regards

Bivin

  • 0 in reply to Bivin George
    TI__Mastermind 32955 points

    Hi Bivin,

    If you want to generate 5V from 5.5V using the TPS7A57 then connect the CP_EN pin to VIN and use the internal charge pump instead of BIAS.  The BIAS pin can be left floating.  I had an EVM (TPS7A57EVM-056) readily available so I quickly confirmed this will work.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    Expert 1027 points

    Hi Stephen

    Thanks for the reply.

    As per datasheet, please see below description for UVLO conditions.

    Will the above cause an issue , in any situation, if bias pin is left floating since UVLO is based on independent conditions?

    In the above mentioned case of using CP_EN pin, will there be an issue if the BIAS is connected to supply voltage of 5.5V ?

    Regards

    Bivin

  • +1 in reply to Bivin George
    TI__Mastermind 32955 points

    Hi Bivin,

    I tested the EVM with the BIAS connected to VIN, GND and floating.  In all cases the output voltage regulated to 5V.  There will be no issue for you, however you connect the BIAS pin.  Internally the LDO will switch to the charge pump and use that to generate the internal bias rail needed to operate the LDO.  The BIAS pin will not be used.

    There are examples in the Typical Characteristic curves where BIAS is grounded, tied to Vin, or tied to a voltage higher than Vin, with various connections of CP_EN.  If you are using the internal charge pump you can do what you want with the BIAS pin as long as you stay within the abs max rating of this pin.

    Thanks,

    Stephen