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TPS7B85-Q1: Some configuration questions

Zirui Su
Expert 5340 points
Part Number: TPS7B85-Q1

Hi

For TPS7B85Q1 application, I have the following questions:

1. If PG only outputs high or low levels, then PGADJ is grounded. I think there is a pull-up resistor inside the IC, so there is no need for an external pull-up resistor, right?

2. How to configure the external resistance of the SENSE_IN and SENSE_OUT of the IC? Is it possible to achieve low voltage detection function? For example, SENSE_OUTPUT is low at 5.9V and high at 6.6V. What is the IC internal VEF voltage value?

  • 0
    TI__Mastermind 23361 points

    Hi Zirui, 

    1. If PG only outputs high or low levels, then PGADJ is grounded. I think there is a pull-up resistor inside the IC, so there is no need for an external pull-up resistor, right?

    The PG pin has an internal pull-up resistor, so no need for an external pull-up resistor.

    2. How to configure the external resistance of the SENSE_IN and SENSE_OUT of the IC? Is it possible to achieve low voltage detection function? For example, SENSE_OUTPUT is low at 5.9V and high at 6.6V. What is the IC internal VEF voltage value?

    The sense monitoring level is predefined as the following that cannot be changed. The SO can be pulled up to a different rail as discussed in 8.1.7.

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    TI__Expert 5340 points

    Hi Jason

    Thank you and could you let me know the VREF specific value?

  • 0 in reply to Zirui Su
    TI__Mastermind 23361 points

    The typical value of Vref used for SI and SO are 1.21V. 

  • 0 in reply to Jason Song
    TI__Expert 5340 points

    Hi Jason，

    Got it. Besides, after I calculating the Vmon（rising) and Vmon(falling)， they are almost the same value so I am afraid of the stop voltage and start voltage, here is the calculation result:

    So could you help me to solve the concern that Vmon(falling) and Vmon(rising) too close?

  • 0 in reply to Zirui Su
    TI__Mastermind 23361 points

    The data you shared are from three different units, right? 

    Unit 1 Vthrising = 1.17, Vfalling = 1.07, Hyst = 100mV

    Unit 2 Vthrising = 1.21, Vfalling = 1.12, Hyst = 90mV

    Unit 3 Vthrising = 1.25, Vfalling = 1.15, Hyst = 100mV

    As you can see, the Vthrising and Vthfalling could vary, but the hyst between the two for an individual unit stays around 90-100mV. Does this address your concern?

  • 0 in reply to Jason Song
    TI__Expert 5340 points

    Hi Jason,

    Sorry for the response late. My concern is that could it be possible that Vthrising=1.17V and Vthfalling=1.15V (it will be hard to do the UVLO under this circumstance) or there is a correspond relationship between Vthrising and Vthfalling, in another way to say that when Vthrising is 1.17V could Vthfalling be 1.15V or when Vthrising is 1.17V, meanwhile Vthfalling is just equal to 1.07V? What is the corresponding relationship between Vthrising and Vthfalling? Thank you. 

  • 0 in reply to Zirui Su
    TI__Mastermind 23361 points

    There is a corresponding relationship between Vthrising and Vthfalling which will make the hyst(Vthrising - Vthfalling) to be around 100mV. 

  • 0 in reply to Jason Song
    TI__Expert 5340 points

    Thanks very much Jason!