• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 62 subscribers
  • Views 274 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

BQ76940: TIDA-010074 schematic query

BQ76940: Query on Design Guideline of TIDA-010074

Pankaj Jain1
Prodigy 10 points
Part Number: BQ76940

Query: Q23 MOSFET has Part no ZXMP10A13FTA  which has VGth -2.0V to -4.0 V & if the op-amp Vss current is greater than 2uA /4 uA then Q23 will turn ON & op-amp Vss will pull down to Cell0 (GND). In this case, Vcc at op-amp is Bus voltage which as per our design is 62 V for LFP Cell. In this condition, op-amp would fail.

Let me know your thoughts

With regards,

P.K.Jain

  • 0
    TI__Guru 54715 points

    Hi P.K.,

    Q23 is used as a source follower or common drain amplifier configuration to provide a voltage slightly higher than Cell 13 as a negative supply voltage for the op-amp.  If the op amp draws more current the source will try to rise increasing VGS and more current will flow to the drain.  If the op-amp current load drops and the Q23 source tried to pull down toward GND the FET will turn off, the source will be held at the gate voltage (cell 13 level) by 1M RGS resistor.   In either mode the transistor will have about 13 cells' voltage between source and drain.  

    A negative voltage regulator would also work for the op-amp supply.  It would provide a more consistent voltage but would take more components & bias current.