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TPS7B7702-Q1: Sense pin connection when not used

Alpha Han
Expert 3750 points
Part Number: TPS7B7702-Q1
Other Parts Discussed in Thread: TPS7B7702

Hi,  Team:

Can you help to check if there is risk to connect the Sense2 pin to GND with 10Kohm resistor when not used? Customer test and find there is oscillation in the pin with scope measure. 

Besides, customer find one system fail. Measure and find VCC to GND resistor is 0ohm and EN2 to GND resistor is about 40ohm. 

Need your help to check and give some advise.TPS7B7702.docx

Schematic and waveform showed in attached file.

  • 0
    TI__Mastermind 23361 points

    Hi Alpha, 

    Based on the current from the output2, we normally recommend to have Rsense < = 2.4 x 198 / 0.057 = 8.3K Ohms. You may connect the 10kOhms resistor but as the datasheet suggested. At the same time, have you tried to connect the required 1uF capacitor to stabilize the current sense loop?

    When not in use, I would suggest you disable the current sensing function /SENSE_EN, /SEN_SEL pins. Or you could simply leave the Sense 2 open. 

    Will you also provide more details on what tests have the customers tried before they saw the failures?

    Regards, 

    Jason Song

  • 0 in reply to Jason Song
    TI__Expert 3750 points

    Hi, Jason:

    Do you see any risk for the oscillation that will damage the device?

    According to customer, they are doing the system test which should include output short to GND and Battery test. 

  • 0 in reply to Alpha Han
    TI__Mastermind 23361 points

    Hi Alpha, 

    We should not have any kind of oscillation in an application in the first place. I would strongly recommend fixing the oscillation by understanding why it's oscillating and takes actions to the SENSE pin if the application does not need it. 

    In order to give recommendations on the failures, will you provide more details such as scope-shots and detailed procedures on how the customer is testing the devices? 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    TI__Expert 3750 points

    Hi, Jason:

    Thanks for the feedback.

    the waveform showed in my former attached. In customer application, they need to use the Channel 1 current sense function. So, they can't disable the function. 

    For Sense 2, please suggest how to connect if not used. In our datasheet, it recommend connect to GND, can you suggest if need to add certain value resistor? 

    And in your former feedback, it recommend left the sense 2 open. 

    Can you double check and advise which one we need to use? 

  • 0 in reply to Alpha Han
    TI__Mastermind 23361 points

    Hi Alpha, 

    When sense 2 is not used, you can ground it or leave it open. By grounding it may help to dissipate heat from this pin to the ground pin copper, and this is recommended by the datasheet. 

    Regards, 

    Jason Song