• State Resolved
  • Locked Locked
  • Replies 12 replies
  • Answers 1 answer
  • Subscribers 65 subscribers
  • Views 317 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.

TPSF12C1: CINJ capacitance and TVS spec

Hirotsugu Kobayashi
Mastermind 9055 points
Part Number: TPSF12C1

Hi team,

It seems that the specification uses CX2 between the common mode choke to inject reverse phase to the L side, is there a definition of the capacitance relationship between CX2 and CINJ?

It is said that INJ is pulled down in shutdown mode, but what happens to the SENSE and INJ pins when the power is off?

A 24V TVS is inserted to protect the injection capacitor CINJ, but what is the reason for choosing 24V?
The absolute maximum rating of the INJ pin voltage is VDD, so I have doubts about using a 24V product instead of a 18V product.

Best regards,

  • 0
    TI__Guru 59837 points

    Hi Kobata-san,

    Yes, you can use Cx2 to provide a CM low impedance across the power lines. Another option is to use two inject caps, one to each power line. The X-cap should have low ESL, such that it's self-resonant frequency is >1 MHz.

    When the IC is unpowered, the INJ pin is floating. Also, there is 10kΩ from each SENSE pin to GND under all conditions.

    The TVS is located at the bottom of the inject capacitor, not at the INJ pin. The damping network impedances appear in series and prevent any overvoltage.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Mastermind 9055 points

    Hi Tim-san,

    Is there a capacity relationship between CX2 and CINJ?

  • +1 in reply to Hirotsugu Kobayashi
    TI__Guru 59837 points

    No, Cx2 and Cinj are independent of each other.

  • 0 in reply to Timothy Hegarty
    Mastermind 9055 points

    hi, Tim-san,

    According to application notes and data sheets, CX2 has a large capacitance of 2.2uF.

    I think one of the reasons for this is injection into the L phase.

    Are there any regulations regarding how many uF or more is required?

    Is the TVS at the CINJ terminal a protection element to suppress ringing that occurs in the damping network?

  • 0 in reply to Hirotsugu Kobayashi
    TI__Mastermind 40055 points

    Hi Kobayashi-san,

    Hirotsugu Kobayashi said:
    Are there any regulations regarding how many uF or more is required?

    Depending on the design requirements, adding more X-capacitance will increase the reactance power consumption. Also, a safety resistor must be used to bleed the energy that is stored in a X-capacitor. Safety regulations stipulate that when a power cord is unplugged, the voltage of either terminal must be less than 30% of the original rated applied voltage.

    Hirotsugu Kobayashi said:
    Is the TVS at the CINJ terminal a protection element to suppress ringing that occurs in the damping network?

    Adding a TVS protects the INJ pin from a surge event. The INJ capacitor is in the nF range and therefore the voltage at the other side of CINJ can increase above the ABS MAX voltage rating of the INJ pin. To protect the INJ pin from an over voltage event, such as a surge event, adding a TVS diode will provide voltage clamping to the INJ pin.

    Ben

  • 0 in reply to Ben C
    Mastermind 9055 points

    Hi Ben-san,

    Please tell me how I should decide the capacity of CX2. Is it necessary to cut and try using 2.2uF as the starting point?

    If the TVS protects the INJ terminal, won't the 24V TVS exceed the maximum rating?

  • +1 in reply to Hirotsugu Kobayashi
    TI__Mastermind 40055 points

    Hi Kobayashi-san,

    The value of the X-capacitor is determined by the frequency of the differential mode current that the filter is targeting to filter out with the leakage inductance of the choke. The leakage inductance and the X-capacitor values form a corner frequency to mitigate the differential-mode noise. The link below provides some insights for your understanding on DM noise.

    https://www.x2y.com/appnotes/emi/2001.pdf

    The INJ pin has an ABS MAX of VDD which is 18V. When adding a TVS diode, the diode is below the CINJ, or C10 shown in the attached image. During a surge event, the impedance network Zd1, Zd2 and Zd3 play a part in determining the voltage seen at the INJ pin. With a TVS diode of 24V breakdown, the voltage seen at the pin should not be higher than ABS MAX.  

    Ben

  • 0 in reply to Ben C
    Mastermind 9055 points

    Hi Ben-san,

    Since the surge voltage is divided by Zd2 and Zd3, should we consider the TVS standoff voltage as VINJ*(Zd2+Zd3)/Zd2?
    Is there any other reason why the datasheet says 24V?

    Best regards,

  • 0 in reply to Hirotsugu Kobayashi
    TI__Mastermind 40055 points

    Hi Kobayashi-san,

    Yes, that is correct. The impedance of Zd2 and Zd3 will provide a current path to GND and will divide the voltage seen at INJ when a surge event occurs.

    Ben

  • 0 in reply to Ben C
    Mastermind 9055 points

    Hi Ben-san,

    Although the datasheet specifies 24V TVS, the maximum rating for the INJ pin is VDD.

    Can TVS be lower than 24V as long as it is higher than VDD voltage?

  • 0 in reply to Hirotsugu Kobayashi
    TI__Mastermind 40055 points

    Hi Kobayashi-san,

    Yes, the TVS can be a little lower.

    Ben 

  • +1 in reply to Ben C
    TI__Mastermind 40055 points

    Hi Kobayashi-san,

    Are there any further questions regarding this topic? If not, please close the thread by clicking on "resolved".

    Thanks,

    Ben