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TPS2595: how to decide the value of RQODEXT

Noriyuki Takahashi
Genius 10950 points
Part Number: TPS2595

Tool/software:

Hi team 

Could you tell how to deice the value of RQODEXT?

It seems RQODEXT is required accoring to figure 62, however there are no descriptions about how to decide the value of  RQODEXT.

 

RQODEXT is different with RQOD, right?

Regards,

Noriyuki Takahashi

  • 0
    TI__Mastermind 38365 points

    Hi Takahashi-san,

    This is external QOD resistor which is selected by user based on the discharge speed they require in there end application.

    Internally QOD pin also have 19Ohm resistor which will effectively be connected in series with this external resistor

    Best Regards,
    Arush

  • 0 in reply to Arush Gupta
    TI__Genius 10950 points

    Arush,

    Arush Gupta said:
    This is external QOD resistor which is selected by user based on the discharge speed they require in there end application.

    Do you mean that customers need to decide the resistor by evaluating their system?

    Are there any equations to device the external QOD resistor? And they also want to understand how much curren can flow through the resistor in order to decide the size of resistor.

    Regards,

    Noriyuki Takahashi

  • 0 in reply to Noriyuki Takahashi
    TI__Mastermind 38365 points

    Hi Takahashi-san,

    QOD provides a discharge path of resistance (QOD_internal (19Ohms) + QOD_external_resistor). For fastest discharge, don't use external QOD resistance.

    If they want to discharge any output cap, we can use RC discharge rate to calculate the time required and the current flow. 

    An example from datasheet.

    The only consideration which customer should know is junction temperature should not exceed abs max when the discharge is happening. That can be calculated using power dissipation on the internal resistor and thermal co-efficient of the device.

    Best Regards,
    Arush