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TPS51200: About PGOOD at pull-up 5V

Tao_2199
Genius 5770 points
Part Number: TPS51200

Hello,

 

Regarding to PGOOD on TPS51200, my customer is asking some question.

･PGOOD pin is pull-up other power(5V). (it is not connected to Vin)

 Pull-up is 10 kohm.

･Before power on Vin(2.5V), PGOOD pin already has been pull-up other power(5V).


 

(Question)

(1)About above power sequence, is there any problem?

From below thread, I think that there will be no problem on their schematic.

e2e.ti.com/.../735624 PGOOD

My understanding is correct?

 

(2) When power on Vin(2.5V),regardless of PGOOD pin is pull-up other power(5V), PGOOD is output 3.6V.

(Please refer below.)


Why does PGOOD output 3.6V?

Also they confirmed that when PGOOD pin is pull-up 2.5V, it is output 2.5V.

 

(3)According to datasheet, PGOOD output is max 6.5V as Absolute Maximum Ratings.

But it is max 3.6V as Recommended Operating Conditions.

Why is PGOOD output limited on 3.6V?

And is their problem connected with above limit(max3.6V)?

 

Regards,

Tao 2199

  • 0
    TI__Mastermind 24075 points
    Hi Tao,

    First, we suggest to keep PGOOD pull-up voltage below 3.5V as it is in the recommended opration condtiion table.
    Also, we suggest to connect PGOOD to Vin (2.5V or 3.3V) via pull-up resistor if it works in your application.

    When Vin is not applied, TPS51200 internal circuit is not working and PGOOD pin is not controlled.
    If Vin is 0V and PGOOD is connected to another voltage via a small pull-up resistor, PGOOD pin could be pulled up to a certian voltage level. The voltage level is related to the pull-up voltage and pull-up resistor value.

    Thansk
    Qian
  • 0 in reply to Qian Chen
    Genius 5770 points

    Hello, Qian

     

    Thank you for reply.

     I have an additional question.

    They understood to use PGOOD under Recommended Operating Conditions.

    But generally it should be output to 5 V when it is pulled up to 5 V.

    They are asking why PGOOD output is limited on 3.5V.

    Could you please explain about that reason, if possible?

     

    Regards,

    Tao 2199

  • 0 in reply to Tao_2199
    TI__Mastermind 24075 points
    Hi Tao,

    This part was designed many years ago, I don't know the exact reason.
    Below explanation is my guess based on experience. Sorry about it.

    The possible reason is there is a clamp circuit (such at ESD circuit) between PGOOD pin and VIN pin.
    When PGOOD pull-up voltage is equal or lower than VIN voltage, the clamp circuit will not work.
    If PGOOD voltage is higher than VIN voltage, the clamp circuit may work and make PGOOD pin voltage lower than its pull-up voltage.

    Thanks
    Qian
  • 0 in reply to Qian Chen
    Genius 5770 points
    Hello Qian,

    I informed to my customer your answer and understood about it.
    Many thanks!

    Regards,
    Tao 2199