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TIDA-01093: Tida-01093 Upper AFE Clls Discharges Fast compared to Lower AFE

smash Micheal
Intellectual 1000 points
Part Number: TIDA-01093
Other Parts Discussed in Thread: BQ76930

Dear All,

Please refer Attached Image of Tida-01093 Schematic, here in Upper AFE Section (Cell-11 to Cell-20) here Cell-12 is used as Input to MosfetQ46, which in turn provides power to U7 Isolator.

Similarly for Wake up of Upper AFE Cell-11 is used to feed Mosfet Q49 Gate , here also i feels Cell-11 is directly used .

Hence looking to Discharge of Upper AFE cells faster than Lower AFE, am planning to replace Q46 input & Q49 input with new Isolated power Supply of 5vdc-5vdc isolated.

Request you to correct me if am wrong or provide me your comments regarding Upper AFE Self Discharge of Cells Faster than lower Afe Cells.(I have used 20s1p cells.) to feed Tida-01093 Board.

Rohit

  • 0
    TI__Guru 54715 points

    Hi Rohit, 

    the images did not show up, so I'm referring back to the TIDA-01093 schematic for the referenced components.

    Q46 is used as a voltage follower or common drain amplifier.  Cell 12 is the reference voltage and the source will be about the Vgsth of the FET below the gate reference voltage.  In the case of the 2N7002-7-F shown it may be around 2V but varies with the current.  See the FET data sheet and your favorite electronics reference on the amplifier type.  No real current is drawn from the reference voltage, current comes from the full stack, to the return point, in this case cells 11-20 as you indicate.  It is an unregulated or poorly regulated linear regulator, so it is not efficient.

    Q49 is used for a similar reference, here for a voltage to wake the upper device.  This would be a pulse.  The connection provides less than a cell voltage at the Q49 source which is then switched to the upper part TS1 when needed for wakeup by Q51. If you replace this reference with a 5V supply be sure to limit the voltage to the TS1 pin. 

    If the concern is that the top cells (C11-20) discharge faster than the lower cells (C1-10), you might look to see if the upper I2C is enabled more than needed.  The Q46 circuit draws about 2-3 uA when off and no current when on, but the I2C isolator will likely draw some mA when on.  If the concern is that the top cells discharge too slowly you could leave the isolator on longer or balance the cells as needed with the upper BQ76930 alternating cells as needed. 

    Other power, switching and interface designs different from the TIDA-01093 can certainly work, select one which suits your methodology and needs.

  • 0 in reply to WM5295
    Intellectual 1000 points

    Hi,

    As u said I have enabled isolator permanently. It is true.

    If I do not do so, I need to switch again and again isolator, which is not a fast action for i2c bus, as data unable to receive at times, so it needs settling delay of approx 1seconds.

    Hence to remove delay I made isolator on permanently.

    Rohit

  • 0 in reply to smash Micheal
    TI__Guru 54715 points

    Hi Rohit,

    I understand better now  If you have the isolator on always you might power it by a dc-dc for better efficiency.  The bottom part voltage domain needs to run the MCU as well as the bottom of the isolator.  There will likely be some signals switched, check the currents for the level translation and balance the load as needed.