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TIDA-01093: Schematic Check

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

Dear Texas Team,

I have taken reference of Tida-01093 eval Board to generate my custom schematic, but in it am facing issue @ L2 part in page 2 of power supply,

if i connect all cells C0-C20, and mount L2 in hardware , than at input of U9 chip minimum input required is 9 volts and max input required is 35vdc, so a range of 9-35vdc is to be given to U9.

Now if my all cells are @ 3.6volts, then output voltage at Q22 pin Drain pin-3 must be 3.6 * 5 = 18 volts(because of source follower ckt of Q21) , but that is not the case , i get near to 11 volts dc. Which is within range of 9-35vdc input range of U9 chip, so U9 gets ON, but after some time of functioning , the input from 11 volts reduces lesser than 9 volts, and hence my U9 gets off.

SO it seems some issue in input side of U9 chip.

Now if i remove L2 and connect power supply from outside which provided volts greater than 9vdc , to input of U9 , that time U9 works properly w/o getting off.

So please suggest where is the issue, am attaching my schematic as well for quik review.

Also please note R76 which is input to Q23 , which if made ON , i will get link to GND , but i have not made ON. Earlier i tried to made ON by applying 3.3vdc from external power supply & i merged gnd of it with my hardware gnd.

Reason for not providing input to R76 from U5 is that, unless i do not turn ON U9 my U10 do not turns ON and hence U5 can not turn ON, once U5 Turns ON it can supply output to R76 pin, so if i wait fo rU5 to turn ON, i can not turn ON my U9, hence before U5 turns ON i need to made U9 turn ON , which can be done only if i apply 3.3 to R76 from outside of Board using Power Supply.

But that is also not working.

RohitE2E Datasheet.pdf

  • 0
    TI__Guru 54715 points

    Hi Rohit,

    In TIDA-01093 the design guide may be very helpful.  In this case it does not describe the source follower circuit of Q21.

    The gate reference for Q21 is VC5X_B, the filtered voltage from 5 cells.  If cells are operated from 3 to 4 V, this will be 15 to 20V.  If your range is different, adjust the values.  The supply for the source follower is BAT+ through R68, a 3.3k resistor.  With 20 cells, BAT+ would be expected to be in the 60 to 80 V range.  R68 will drop 3.3V per mA of load.  The output of the source follower will be approximately Vgsth below the gate reference or slightly more depending on current.  For this FET that is 2-4V, so lightly loaded the source, voltage for R70 and the Q22 switch  would range from 11 to 18 V.  If the Q21 source voltage is dropping look at the current being drawn to see if the drain is being starved by the voltage drop across R68 or if there is some high resistance connection or damaged component.  If R70 is installed the 100 ohm makes for easy math for calculating the current from the voltage across it.

    If current is excessive through L2 consider its load, or check for leakage in C44.  Mornsun will be better able to help you understand your U9 circuit.

    In TIDA-01093 Q23 and Q22 provided a power switch for the U4 LM25018MR regulator which powered the communication circuit.  Power for the MCU came from the bottom BQ76930 monitor, so the MCU could switch that regulator.  In your design, the MCU is powered from U9, U10 which must be on for the MCU to run and control a power switch.  Your communications chip provides its own isolated power.  You may need the Q22 power switch controlled by a different circuit such as the BQ76930 REGOUT, or move it to control different portion of the power system or perhaps you don't need it.  Consider your architecture and power budget.