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BQ76930: BQ76930 charge detection circuit query

Star Xu
Genius 9645 points
Part Number: BQ76930

Hi

I have some queries with charge detection circuit, attached the schematic.

1. What is the role of Q56 in the picture, can it be removed

2. whether Q14 can be removed.

3. Why use four diodes D29, D30, D34, D37

Thanks

Star

  • 0
    TI__Guru 54715 points

    Hi Star,

    I did not design the circuit and have not simulated it.  You may find it valuable to simulate with a tool such as http://www.ti.com/tool/TINA-TI with stimulus similar to your expected system.

    1. Q56 provides a switch with Q16 of the current to the diode string.  It looks like the voltage limit is 33V with the zener and gate voltage limit of Q56.  Q56 was a later addition from its number, it must have had some significance to the circuit.  With a quiescent system it would seem a single FET should handle the Vgs for the VC5X derived voltage at Q14 source.  You might simulate to determine if it is needed in your application.

    2. Q14 provides a limited voltage to the circuit with current from the full cell stack.  Removing it with connection to BAT+ would overvoltage the circuit.  Connecting to VC5X_B would pull unexpected current from the node and shift the operating voltage of the part.

    3. Four diodes will provide a more definite voltage than a low voltage zener as well as block reverse voltage (which would not seem to be an issue here).