• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 192 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC28064A: About CS terminal rating

Kotaro Miyakoshi
Prodigy 20 points
Part Number: UCC28064A
Other Parts Discussed in Thread: UCC28064EVM-004

About the absolute maximum rating of CS
Is the data sheet wrong?
VMAX: 3V, VMN-0.5V (data sheet)
↓
(Correct) VMAX: -0.5V, VMIN-3V

  • 0
    TI__Genius 10555 points

    Hi Kotaro-san,

    I do believe the AbsMax limits for CS pin are correct as written in the datasheet.  That is the limit for voltage on the pin, not where we expect it to normally operate.

    Regards,

    Ray

  • 0 in reply to Ray DiCecco
    Prodigy 20 points

    When AC is turned on, a current of 60A flows through a resistor of 30mΩ at the first shot.

    At that time, -1.8V is applied to the CS terminal.

    It exceeds the absolute maximum rating, is that okay?

    Also, only negative voltage is applied to the CS terminal, but what is the + 3V rating assumed?

  • 0 in reply to Kotaro Miyakoshi
    TI__Genius 10555 points

    Hi Kotaro-san,

    The sense resistor value seems too high. Vcs_dph occurs at -200mV.  Rs should be ~200mV/Ipeak

    What is your output power?

    Regards,

    Ray

  • 0 in reply to Ray DiCecco
    Prodigy 20 points

    Calculated with UCC28064EVM-004, the CS terminal rating is exceeded. is that okay?

  • 0 in reply to Kotaro Miyakoshi
    TI__Genius 10555 points

    Kotaro-san

    Rs should be sized based on peak currents during normal operation, not inrush current.  If it's sized on the inrush current, there will be virtually no overcurrent protection during normal operation.  Basing it on operating conditions will still provide protection to the MOSFETs during inrush but also during current spikes that may occur in normal operation.

    From note(4) under the AbsMax table, the Vcs is allowed to exceed the AbsMax during inrush as long as the -30mA input current isn't violated.

    Also note that from your first diagram, that even with the 30mΩ Rs, -1.8V won't be impressed on the CS pin as the series resistor will be absorbing much of that voltage.

    Regards,

    Ray

  • 0 in reply to Ray DiCecco
    Prodigy 20 points

    Is it okay to judge the CS peak input current (-30mA) at the time of inrush current?

    Please tell me how to calculate the CS peak input current.

    If this is not possible, please tell me how to measure the CS peak input current.

  • +1 in reply to Kotaro Miyakoshi
    TI__Genius 10555 points

    Hello Kotaro-san,

    Limiting the input current into CS to less than 30mA is simply a matter of sizing the series resistor (the resistor between the CS pin and Rs) based on your expected peak voltage across Rs (which should occur during input surge).

    If for instance you calculate the peak voltage (Isurge * Rs) to be (-)1.0V, then the series resistor would should be > 1.0V/30mA or 33Ω.  Of course, you would want some margin so the resistor would be larger than 33Ω.  We typically recommend 100Ω which will cover most situations.

    Let me know if this answered your question.

    Regards,

    Ray 

  • 0 in reply to Ray DiCecco
    Prodigy 20 points
    Thank you for your answer.
    It is solved.