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BQ24450 Application Circuit

Mohit Arora
Prodigy 20 points
Other Parts Discussed in Thread: BQ24450

Dear Sir,

I am looking forward for an application circuit of BQ24450 implemented for a six cell lead acid battery. The circuit should have float *** boost charging with trickle charge. I have done a circuit using the fig 9 of the datasheet with values calculated for 6 cell battery but the system is oscillating between boost and trickle charge mode. Matter is urgent, so share the basic circuit. I can do all the modification for the currents but voltage and feedback paths are important to know. 

 

  • 0
    TI__Mastermind 36110 points

    I agree that the bq24450 datasheet, figure 9 contains the functions you need.  It will be necessary for you to carefully evaluate and measure (with an oscilloscope) the voltages on the pins of the bq24450 so you can determine what part of your circuit is causing the electrical condition that changes the IC between the two different modes.  The first place to look is at the CE voltage because this voltage defines when the bq24450 goes into and out of precharge (or trickle charge).  It will also be important to check the other pins to see if a layout problem might be injecting noise into the circuit which causes the voltages on the bq24450 to change between precharge and boost modes.

  • 0 in reply to Matthew Day
    TI__Mastermind 31120 points

    It is also important to use a real battery during testing since electronic loads often interact with chargers and cause oscillations.

  • 0 in reply to Matthew Day
    Prodigy 20 points

    Thank you Michael,

    I agree to your point and if figure 9 is the correct application scheme,  I can do with the layout and other things but if you could help with  some application circuit with resistance values calculated, i will not end up with a loop of iterations because of odd resistance values and ratio matching. In that case, I think, my problems will be quite lesser. My hope is my value margins for resistance are making the circuit oscillate.

    Please check for any application circuit for 6 cell battery just for the reference of resistance values.

    This is an urgent requirement for a customer and I don't want to lose this opportunity experimenting at his place.

    @Charle: Thank you Charles, but all the testing is being done over the very end product battery.

    Mohit

  • 0 in reply to Mohit Arora
    TI__Mastermind 36110 points

    We have no way to calculate and iterate the calculations faster than you or your customer could do this.  Ultimately you will need to build and test the circuit values on your board and then interate them if necessary to obtain your required performance.  You should not have problems with "odd resistor" values if you use 1% resistors.  Just choose the closest value and your actual tolerance will be closer than 0.5%.  If you need tighter tolerance, you can either use 0.1% resistors or add resistor placeholders in parallel with the existing resistors so you can tweak the values to non-standard 1% resistors.  Before anything is recalculated, it will be important for the troubleshooting to identify the root cause of the oscillations.