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LM20343 / Soft Start discharge

Tsukui Yusuke
Guru 21930 points
Other Parts Discussed in Thread: LM20343
Hi Team,
 
I'd like to ask about LM20343.
Our customer want to know discharge time of the soft-start capacitor.
Could you tell me the current that flows when the discharge of the soft-start?
Or,Could you tell me the resistances value to be used to discharge?
 
 
Best Regards,
Yusuke　/ Japan Disty
 
  • 0
    Guru 21930 points
    Hi Team,
     
    Can I get the information ?
    If you need more information or if  I should  clarify my comment , please let me know.
     
    Best Regards,
    Yusuke　/ Japan Disty
  • 0 in reply to Tsukui Yusuke
    TI__Guru**** 191445 points

    I don't think that group monitors the forum very closely.  Let me see if I can direct someone to reply.

  • 0
    TI__Intellectual 1135 points

    Hi Yusuke,

    I found following description in the datasheet:

    "When the device is enabled there is an approximate time interval of 50 μs when the soft-start capacitor will be discharged just prior to the soft-start ramp. If the enable pin is rapidly pulsed or the soft-start capacitor is large there may not be enough time for CSS to completely discharge resulting in start up times less than predicted. To aid in discharging of soft-start capacitor during long disable periods an external 1MΩ resistor from SS/TRK to ground can be used without greatly affecting the start up time." 

    Which indicates discharge time should be around 50us, and you can add external 1Mohm resistor to speed up the discharge.

    I am also trying to contact the orignal designer/apps engineer to see if they have more details.

    Thanks.

     

  • 0 in reply to Haifeng Fan
    Guru 21930 points
    Hi Fan,
     
    Thank you for your response.
     
    I have contact to the customer information from you already.
    Can not be installed discharge resistance at the convenience of the board of the customer.
    Customer is trying to adjust by increasing the EN off time.
    So customer want to know the time required to discharge.
    Could you tell me the current that flows when the discharge of the soft-start?
    Please contact my question to the designer.
     
    Best Regards,
    Yusuke　/ Japan Disty