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Original question:

LM51501-Q1: LM51501-Q1 - Input feedback resistor

LM51501-Q1: Vout feedback resistor

Arie Li
Expert 3390 points
Part Number: LM51501-Q1

Hi Team,

I have two questions about LM51501-Q1

1. When LM51501 configured in E-call mode, where does the internal logic power supply come from, VIN or Vout?

2. When LM51501 configured in E-call mode, how does it realize different constant output voltage with the internal feedback resistor? From the datasheet, we can set different Rset value to configure different Vout regulation target. Is the Rset resistor same with or related to the lower side feedback resistor? If so, what is the upper resistor value and what is the reference voltage? If not, could you please explain the principle of how  LM51501 realize different constant output voltage? Thank you in advance.

BR,

Arie

  • 0
    TI__Mastermind 21720 points

    Hi Arie,

    Thanks for reaching out with your question and for using the LM51501

    Please see my responses below

    1. When LM51501 configured in E-call mode, where does the internal logic power supply come from, VIN or Vout?

    The device is powered from the VOUT pin in E-call mode.

    2. When LM51501 configured in E-call mode, how does it realize different constant output voltage with the internal feedback resistor? From the datasheet, we can set different Rset value to configure different Vout regulation target. Is the Rset resistor same with or related to the lower side feedback resistor? If so, what is the upper resistor value and what is the reference voltage? If not, could you please explain the principle of how  LM51501 realize different constant output voltage? .

    The LM51501 has programed discrete output voltages that are programed through the RSET resistor. This is not the same as the lower feedback resistor as it programs the output voltage and the mode of operation. Internally there is a circuit that measures the RSET resistor and programs the device correctly.

    Please let me know if you have any questions.

    Thanks,

    Garrett