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LM51772: LM51772 internal

Pabl Oliva
Prodigy 25 points
Part Number: LM51772

Hi,

In our application of the LM51772, I intend to utilize internal feedback. I understand that the LM51772 is equipped with OTP (One-Time Programmable) memory. How can I modify the default values of the VOUT_TARGET1_MSB and VOUT_TARGET1_LSB registers so that upon startup, without any adjustments to the registers, the default output voltage is 12V instead of 5V, assuming the LM51772 is enabled? I would like to know the process for achieving this.

  • 0
    TI__Guru 55101 points

    Hi Pabl,

    thanks for using the E2E forum.

    When using the internal FB divider the output voltage can be set for the LM51772 but only via I2C interface. It can not be set by programming an OTP memory inside the LM51772.

    Note: It is planned for the final device to set the default output voltage with internal FB divider to 12V instead of 5V which was set for the first devices used for the prototype devices.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    Prodigy 25 points

    Hi Stefan, 

    Thanks for your reply.

    About your Note, what do you mean by this? The available LM51772 in the market will have its default internal feedback set to 12V? 

    Could I use a PMOS to connect and disconnect the FB pin from VCC2? In this case, I can have this PFET off in normal operation and use external feedback. If I need to change the voltage I can disable the IC using the EN pin, turn on the PFET to connect the FB pin to VCC2, and change to internal feedback.  Is this plan reasonable?

  • 0 in reply to Pabl Oliva
    TI__Guru 55101 points

    Hi Pabl,

    can you briefly describe your requirements, this would make it easier zo recommend the best solution.

    Best regards,

    Stefan

  • 0 in reply to Stefan Schauer
    Prodigy 25 points

    Hi Stefan, 

    What I need is when I power up my system and the LM51772 gets power, it automatically starts at 12V at the output. But only if I need to change to voltage, I use the I2C communication to change to output voltage.  

    With the idea of using a PMOS to connect the FB pin to VCC2, I could start the converter with external FB, and only if necessary I could disable using the EN pin, connect FB to VCC2 turn on the PFET, change the voltage internally, and then turn on the converter using the EN pin. 

    How could I get LM51772 parts with the 12V as the default output voltage?

  • +1 in reply to Pabl Oliva
    TI__Guru 55101 points

    Hi Pabl,

    the device you currently get and also the Datasheet on the web is for the experimental silicon (also marked with XLM51772).

    The final released devices will have an default output voltage of 12V when the internal FB is enabled.

    The will be prototype devices (next level of preproduction devices) marked with PLM51772 available in ~ 4 weeks.

    This will already have the output voltage set to 12 V as default for the internal FB divider.

    Best regards,

     Stefan