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Original question:

BQ76940: schematics review

BQ76940: schematic design questions

minqi zhao
Prodigy 20 points
Part Number: BQ76940

Dear Ti Experts,

I'm designing a product with bq76940 and I have a few schematic questions. Please help me to figure it out.

Q1:I noticed that a diode is connected from VC5 to VC5X in applicaion of bq76940. I wonder why and can this diode be eliminated or directly short?

Q2:There's a paragraph titled reduced test time saying that a special debug and test configuration bit is provided in the SYS_CTRL2 register, called [DELAY_DIS]. Setting [DELAY_DIS] bypasses the OV/UV protection fault timers and allows a fault condition to be registered within 200 ms after application of such a fault condition. I'm confused about how the test time be reduced.Can you explain it more clearly?

Thanks a lot.

  • 0
    TI__Guru 54715 points
    Hi Minqi,
    1. The diode prevents damaging voltage on VC5 which can leave the pin unable to report the full voltage at the pin. The diode should be a conventional diode since the VC5X pin will fluxuate some in operation and it is undesirable to have the diode conduct in normal operation. For this reason a schottky type diode is undesired and a direct short would also load the pin and report improper voltage for cell 5. See figure 20 and related discussion in www.ti.com/.../slua749a.pdf
    2. DELAY_DIS shortens the digital delay before OV/UV. If testing 15 cells for a 4 second delay, the test time would be 15 x 4 = 60 s or more. Using the DELAY_DIS feature the test time for 15 cells would be 15 x 0.2 = 3 s or more. So DELAY_DIS could save 57 seconds per test. Of course it depends on the timing selected for the design.