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BQ77915: Vocd settings

HARINI KRISHNA
Expert 1905 points
Part Number: BQ77915

Hi,

In the data sheet Section 8.5, page 8, it is given that Vocd is programmable. 

https://e2e.ti.com/support/power-management/f/196/t/857753 this post says that it cannot be programmed.

Can it be programmed by user or not?

if i need the device to support 8 A discharge current, as said by the post, ( VOCD1= 60mV if bq7791500 is chosen)

60mV/ 8 A = 7.5mohm. 

So, i need to choose 7.5mOhm sense resistor to let the device support 8 A?

Why do we have VOCD1 and VOCD2? What is the purpose of having  two VOCD values?

 Thank-you

Warm regards

Harini Krishna

  • 0
    TI__Guru 54715 points

    Hi Harini,

    The OCD thresholds can not be programmed by the user.  They are programmed at the factory in the range shown in section 8.5.  Parts presently defined are shown in section 6, https://www.ti.com/document-viewer/BQ77915/datasheet/device-comparison-table-slusbz71191#SLUSBZ71191 .

    Right, if you are selecting the resistor for the OCD threshold you would select a 7.5 mOhm resistor as you show.  Usuallly a designer will make a choice of several thresholds considering tolerance and whether they are designing for a must-trip current or a must-operate current. 

    Some systems are only concerned with a single threshold.  The BQ7791500 was configured for such a system with both OCD thresholds at the same level.  Other systems may have a requirement to run continuously with a certain current, with a higher current they should trip after a relatively long time but with a higher current still much less than short circuit they should trip at a shorter time.  BQ7791501 has different thresholds, delays would be selected with the OCDP resistor.  BQ7791506  has different delays and thresholds selected.