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LM3253: Inquiries about LM3253

JH Shin
Mastermind 7990 points
Part Number: LM3253

Hello,

My customer has some questions about the LM3253.

1. They found that the LM3253 datssheet contains the following startup sequence and conditions.

    If EN is grouped with VIN and operated at the same time, could the IC not recognize EN and fail to operate?

2. Could you please provide the gerber file of the LM3253EVM?

Thank you.

JH

  • +1
    TI__Genius 15040 points

    Hi JH,

    The datasheet recommends disabling the device via EN when VIN < 2.7V. This is because there is no UVLO detection circuitry implemented for VIN. There may even be a possibility that the output regulates to a wrong voltage if not done so.

    I have attached the gerber files for the LM3243EVM. It is the same as the LM3253EVM.

    SV600725C_Gerber.zip

    Best regards,

    Varun

  • 0 in reply to Varun John
    Mastermind 7990 points

    Hello,

    The customer has further questions about the symptom.

    1. Can the device output be 0V as one of the symptoms of 'the output regulates to a wrong voltage if not done so' you mentioned above?

    2. When they reproduced the symptom, the error symptom occurred with a higher probability at low temperature (-10 degrees) than at room temperature (+25 degrees), and it occurred more frequently as the rising time of the input power supply(+3.3V) was longer.
    We ask for your opinion on the relationship between these two variables (temperature and power rising time) and the error occurrence probability.

    Thank you.

    JH

  • 0 in reply to JH Shin
    TI__Genius 15040 points

    Hi JH,

    This is a pretty old device inherited from National times. We have quite limited data on this. I didn't find anything for the condition where EN and VIN are tied together probably since it's not the recommended operating method. I believe it's possible to get a wrong output voltage including 0V, if both VIN and EN are tied together. This could be because of a wrong readout of the device settings from the internal EEPROM memory at a low VIN when the converter is enabled. If the device is enabled at a VIN>2.7, the EEPROM should be read correctly. This error correlates with a slower VIN rising time, as the EEPROM readout requires a certain time and the slower the VIN ramp is, the greater the chance that VIN was lower than the required level when this readout happens. 

    Best regards,

    Varun