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LP8758-E0: About dropout voltage

Yuto Sakai
Mastermind 6100 points
Part Number: LP8758-E0


Hi,

Could you tell me about "dropout voltage" of LP8758-E0.

"Dropout voltage" is written as min 0.7 V on datasheet P.6.

Is this guarantee value relaxed by load current?

If yes, please tell me the load current condition at min 0.7V.

Best Regards,

Yuto Sakai

  • 0
    TI__Genius 16410 points
    Hi Sakai-san,

    Typically, the dropout requirement will be smaller at lower load currents, but I'm not sure on the load condition for dropout for this device. I'm looping in the device expert, he will respond to your question.

    Regards,
    Karl
  • 0 in reply to Karl Wallinger
    Mastermind 6100 points

    Hi Karl-san,

    Thank you for your reply.

    I'm looking forward to his answer.

    When can I get the answer?

    Best Regards,

    Yuto Sakai

  • 0 in reply to Yuto Sakai
    TI__Genius 13860 points
    Hi Sakai-san,

    This drop-out voltage specification is not relaxed by load. 0.7V drop-out fulfills that device is capable to provide maximum current and there is no other specification for this.

    Best regards,
    Jari Niemelä
  • 0 in reply to Jari Niemela13
    Mastermind 6100 points
    Hi Jari-san,

    Thank you for your reply.
    In other words, when it is not 4A supply, is it even better if VIN-VOUT <0.7V?

    Best Regards,
    Yuto Sakai
  • 0 in reply to Yuto Sakai
    TI__Genius 13860 points
    Hi Sakai-san,

    Yes, in the other words it is even better if VIN-VOUT is greater than 0.7V.

    Best regards,
    Jari Niemelä
  • 0 in reply to Jari Niemela13
    Mastermind 6100 points
    Hi Jari-san,

    What is the risk when VIN - VOUT is less than 0.7 V?
    The load current is expected to be around 0.5 A.

    Best Regards,
    Yuto Sakai
  • 0 in reply to Yuto Sakai
    TI__Genius 13860 points
    Hi Sakai-san,

    I would not say a one risk. Datasheet parameters are measured under specified conditions. If drop-out voltage specification is not met other parameters can possibly fall outside specification also.

    Best regards,
    Jari Niemelä
  • 0 in reply to Jari Niemela13
    Mastermind 6100 points

    Hi Jari-san,

    Thank you for your kind surpport.

    Sorry to bother you often.

    Is it difficult to guarantee the dropout voltage under certain conditions as well?

    The condition is Vin = 3.08V, Iout = 500 mA.

    Is it a parameter indicating that this dropout voltage regulation can not be set to 100% duty?

    Best Regards,

    Yuto Sakai

  • 0 in reply to Yuto Sakai
    TI__Genius 13860 points

    Hi Sakai-san,

    Your are welcome. No problem.

    For certain condition it would need a specification change and new simulations and validations as well.

    If you have Vin=3.08V and current 500mA but how much is Vout ?

    Dropout voltage is ratio between VIN-VOUT and how close to each others voltages can be and converter is still able to provide full current. We have not specification for this at lower VIN-VOUT ratio levels or with lower current. In this datasheet dropout does not mean that high-side switch is fully open, it is condition to meet specifications.

    I hope this helps.

    Best regards,

    Jari Niemelä

  • 0 in reply to Jari Niemela13
    Mastermind 6100 points
    Hi Jari-san,

    Thank you for your kind reply.
    Our custormer's Vout condition is 2.9V.

    That means that the dropout voltage is a condition that meets specifications and does not include the meaning of maxDuty?
    Even if VIN - VOUT moves less than 0.7 V normally, should it be considered that there is a possibility that it may not move as specified due to variations in IC etc?
    Since customers operated normally under the above VIN, VOUT, and IOUT conditions, they expect to be able to move.

    Best Regards,
    Yuto Sakai
  • 0 in reply to Yuto Sakai
    TI__Genius 13860 points
    Hi Sakai-san,

    Yes, dropout means exactly that all other specifications will be met with VIN-VOUT equal or higher than 0.7V. It is not related to max duty cycle.
    Device is functional under 0.7V dropout but other specification might not be met on very condition.

    Customer can operate below 0.7V dropout but they are responsible to validate that device behavior is acceptable.

    Best regards,
    Jari Niemelä