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BQ76940: BQ76940 TSX Iissue

Big Bill
Expert 1980 points
Part Number: BQ76940

Dear  All:

       there are  no 10K resistor  pull down with TS2 to VC5X and  TS3 to VC10X in my MP products. Also about 1%  of the 2000 products ，X-ready indicate “1”, I can't clear the bit by the MCU command. I need to 

reset  the BQ76940 power supply， the products are Good.  I try connect the TS2 to VC5X and TS3 to VC10X by the pull down 10K resistor. the the X-ready can be clear by the MCU.

   Question:   what condition can cause the X-ready indicate  “1” and can't be clear by the MCU  in no pull down resistor, it doesn't looks like  100%  occur ？

  • 0
    TI__Guru 54715 points
    Hi Bill,
    The bq76940 is intended to be operated with pull down resistance on the TSn (TSX, TS1, TS2, TS3) pins. Without the pull down resistance voltage can be trapped on the TS2 or TS3 pins and at boot the upper group power will not start. This results in the XREADY fault. This is common at board test if thermistors are designed in a battery cable harness which is not attached at the time of test. The use of capacitors on the inputs to reduce noise tends to hold the voltage on the pins and the condition can last through some power cycles, but may go away if the power to the board is left off for some time.
    Another possibility is the connection of the thermistors or pull down resistors for TS2 or TS3 to the device VSS rather than the group power reference pin (TS2 to VC5X, TS3 to VC10X). The current out of the TS2 and/or TS3 pins violates the abs max voltage level of the pin and can prevent that upper group from starting again resulting in the XREADY fault.
    The TSn pins are inputs as shown in the data sheet section 5.4.1 bq76940 Pin Map table. As indicated in the note 1, if not used they must be pulled down to the appropriate reference.