• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 242 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.

TPS566235: Output discharge function

Takashi Yamaguchi
Genius 11090 points
Part Number: TPS566235
Other Parts Discussed in Thread: TPS563211, , TPS568230

Hi team,

It seems that TPS566235 doesn't have the output discharge function, but can the Power good-pin be used for output discharge like TPS563211?  The section of "7.3.5 Output Discharge through PG/SS Pin" in the d/s of TPS563211 describes that PG-pin can be used for output discharge.

Regards,

Yamaguchi

  • 0
    TI__Expert 7500 points

    Hi Yamaguchi,

    I will double check with our design team whether TPS566235 has discharge function. Will feedback to you on Monday.

    Yes, all the open-drain PG can be used for output discharge by connecting PG to Vout through a resistor. But the discharge time will be very long than dedicated discharge circuit. For the PG to Vout resistor, the level should be several Kohm or tens of Kohm or 100K. While for dedicated discharge circuit, the discharge resistor level is hundreds of Ohm. For example, TPS568230 discharge resistance is 420 Ohm. The discharge time will be fast.

    Thanks,

    Lishuang

  • 0 in reply to Lishuang Zhao
    TI__Genius 11090 points

    Hi Lishuang-san,

    Thank you for the answer. TPS568230 looks good.

    If you have an information on the minimum value of pull-up resistance that can be connected to the PG pin of TPS566235, or the maximum value of current that can flow through the Power Good FET, could you let me know?

    Regards,

    Yamaguchi

  • 0 in reply to Takashi Yamaguchi
    TI__Expert 4570 points

    Hi Yamaguchi,

    For the sink current ability of PG you can refer to the IPGSK in datasheet.

    Regards,

    Andrew

  • 0 in reply to Andrew Xiong
    TI__Genius 11090 points

    Hi Andrew,

    Thank you for the answer. 

    The PG Sink Current is described as 52mA(typ) in the datasheet. For safety, I would use 52mA x 0.8 = 40mA as min value. In the case of 3.3V output, customer can connect  3.3V / 40mA = 82.5ohm(min) between PG-pin and Vout. Please correct me if I'm wrong.

    Regards,

    Yamaguchi

  • 0 in reply to Takashi Yamaguchi
    TI__Expert 7500 points

    Hi Yamaguchi,

    When finding the minimum value for RPull-up, it is assumed PG open drain fet is turned on, so VPG is shorted to ground. In reality, the fet has a resistance, RDSon, which will drop some voltage and cause the PG voltage to be above ground potential. When the fet is on, the PG voltage must be sufficiently low to
    register as a logic low to subsequent circuitry.

    The PG voltage is the divided voltage of pull up resistor and open drain Rdson from pull up voltage. So in your hypothesis, using 82 Ohm pull up resistor and 5Vout，PG voltage can be calculated as 5V*(0.5V/52mA)/(82 Ohm +0.5V/52mA)=0.524V which may higher than subsequent circuitry logic low threshold. So that can't disable subsequent circuit.

    So please according your application to decide the PG pull up resistor.

    Detailed can be checked in the attached link.

    https://www.ti.com/lit/an/slva485/slva485.pdf

    Thanks,

    Lishuang