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BQ24780S: NiMH

Ilya Mazurenko
Expert 1300 points
Part Number: BQ24780S
Other Parts Discussed in Thread: BQ2000, BQ2000T, BQ24765

Hello,

We are using NiMH battery and we will need 50-64mA charging current

We have several question about BQ24780S:
1)BQ24780S didn’t support NiMH before March 2017, did it?(I haven’t found it in parametric search 3 weeks ago)
Now on the BQ24780S web page lists NiMH.
But there are no confirmation in datasheet.
So does it support NiMH chemistry?

2)We will need 50-64mA charging current
On the page 32 of datasheet described that charge current controls by register from 128mA to 4A with 10mOhm resistor(table below).
Can we just write logic 1 to 6bit to make charge current 64mA?
Or do we need to write logic 1 to 7bit to make charge current 128mA and use 20mOhm resistor to decrease charge current to 64mA?

3)There are NO any graphs for constant current charging mode/constant voltage charging mode.
Can you provide this graphs to us. Datasheet don’t provide it.
Also the description of paragraph 7.3.3 is not complete.

4)Due to the question 2), if we will use only 7bit of charging current and 20mOhm resistor(to make it 64mA) what values of the resistors should be for the R10/R11?(For the correct working ILIM)

Ilya.

  • 0
    TI__Mastermind 19430 points

    780S is a targeted for notebook applications. When charge current is only at 50 to 64mA, we do not recommend to use this device. The bq24780S is designed for higher charge current thus the charge accuracy at such low current will be low.

    The reason it is a NiMH charge is that this device is a host control charger which host initiates charge and decide when to terminate. Thus it can charge multiple chemistry relying on the host control. This also the reason we do not include the charge profile in the datasheet since it relies on the host control.

    NiMH battery does not use CC/CV charge profile.

    For NiMH charger, we recommend to have a look on bq2000 or bq2000T. This is a charge controller specifically made for Ni batteries. Reference design can be found in the EVM user guide.

  • 0 in reply to Jing Zou
    Expert 1300 points
    Hello,

    We need industrial temp range, but no one charger from BQ200x family support it.

    The only other variant for NiMH is BQ24765...
    We hoped BQ24780s could be That material(it cost half less)

    +/- 30% accuracy is not big problem

    Ilya.
  • 0 in reply to Ilya Mazurenko
    TI__Mastermind 19430 points

    Can you please let us know what the industrial temperature range you are looking for?

  • 0 in reply to Jing Zou
    Expert 1300 points
    -40 to 85

    Ilya.
  • 0 in reply to Ilya Mazurenko
    TI__Mastermind 19430 points

    For your temperature range, bq24780S is probably the one to use. 

    Again, for host controlled chargers, the charging profile is controlled by the host. The charge itself is only a slave.

  • 0 in reply to Jing Zou
    Expert 1300 points
    Could you provide to us please charging profile for NiMH(+BQ24870S) for host controller?
    This is very important project with big annual volumes.

    Ilya.
  • 0 in reply to Ilya Mazurenko
    TI__Mastermind 19430 points
    What is the end equipment and what is the projected volume? We would like to understand what is the main reason to use NiMH battery.

    Bq24780S is a host control version SMBus charger. The host controller controls the charging profile. To find a right charging profile, please give us the application detail:
    1. Is it a frequently charging and discharging application?
    2. Does this battery need a short charge time?
    3. Does the ambient temperature change during the charge?

    For a non-removable battery and small charging current rate, we recommend constant charging current to charge it.
    For a frequently charging and discharging application, we recommend a high charging rate and host controller monitors the dv/dt and dT/dt of the battery cell to terminate the charging at right time. ….

    We also recommend to consult with your NiMH battery manufacturer on their recommended charging profile.