BQ2002D: Single cell configuration

The resistor divider network RB1 and RB2 will not be used.
IC will still be powered from a 5V supply and control a current source supply to the battery.

Hi Bill,

Thank you for your support.

If RB1 and RB2 is not necessary, can we connect the battery to BAT pin directly?

If that is able to, VBAT which is single cel voltage is always within VMCV(2V). (It is just the always the state of charging.) Is it possible?

Regards,

Koji Hamamoto

Hi Bill,

Could you follow the previous question?

And regarding to the previous question,do you think this device (BQ2002D/T) are suitable for an single cell battery such as NiMH which is low voltage battery (1.2V typ)?

Regards,
Koji Hamamoto

Hello
The bq2002 will control the external current source that will apply charge current / voltage to the battery. This is typically the LM317 configured as a current source. Battery voltage would be applied directly to the BAT. Recommend adding a resistor position between battery and pin.

Hi Bill,

Thank you for your prompt reply.

>Battery voltage would be applied directly to the BAT. Recommend adding a resistor position between battery and pin.

 I don't  understand how we can add the resistor between BAT pin and battery. Does it mean that add in series? (Is that the following configuration?)

   

 Also if the battery(single cell=1.2V typ) is connected to BAT pin directly, BAT pin voltage is always below VMCV(2V).

 I think this state is always charging state even if it is full charged. That is why I asked can this device be suitable for single cell battery.

Could you advice me if my understanding is not enough?

 

Regards,

Koji Hamamoto

Hi Bill,

I have one more question. (I am sorry to bother you when you're so busy.)

As you mentioned above, you recommended LM317 for current source. Is TPS7A8101 possible for the current source as well?
(The CC signal<CC=High> from CC pin is enable TPS7A8101 at charge state.)

Regards,
Koji Hamamoto

Hello

I am working on setting the bq2002 up in the lab in a single cell configuration to evaluate some of this.  What is your charging current?

Have not used the TPS7A8101 in this configuration.

Hi Bill,

I appreciate your support.

I will check the charge current to the customer. Then I will let you know.

Regards,
Koji Hamamoto

Hi Bill,

I got the information.
The charge current is 600m~700mA by the current mirror. And they will use 3700mAh~4500mAh the NiMH battery.
Please let me know if single cell configuration works better at your measurements.

Regards,
Koji Hamamoto

Hi Bill,

Do you have any update for this? Did you get any result on your evaluation?

Regards,
Koji Hamamoto

Sorry for the delay

I have a 2 series cell version working but having problems with a single cell version.

Will try to have more info this week

Hi Bill,

I appreciate your support. And I understand you are very busy. However our customer are going to use this device with a single cell version.

If the single cell version is not acceptable for this device because VMCV_min of this device is 2V, I need to suggest the another device which is supported the single cell.

I understand you will need to try with a board.
But do you think the VMCV of this device is able to change for supporting the single cell of NiMH?

Regards,

Koji Hamamoto

The BAT voltage will be a single cell voltage representation provided by RB1 and RB2 for mult-cell configuration. For a signal cell only RB1 is used, RB2 is open.

Charge can be terminated if the cell voltage reaches the Maximum Cell Voltage (VMCV) of 2V +/-5%, even in the single cell configuration. But a typically NiMH single cell voltage (1.2V to 1.6) will be below this point.  Fast charge is terminated by a drop in cell voltage or rise in cell temp.

The bq2002D will use Rate of Temp rise. Thermistor (NTC) is in contact with the cell to monitor temp.

The bq2002C will use drop in cell voltage or Negative Delta Voltage. The cell voltage in monitored at the BAT pin.

VMCV of 2V applies to both.

Hi Bill-san,

I appreciate your kind support. That was very helpful information.

Can I ask two more question?

1. The configuration what you mentioned is like the following configuration. 

  However how can we calculate RB1? What is RB1 for?

2. You selected BQ2002D and BQ2002C as above. Why you did not select BQ2002T?

    Do you have any reason to not select BQ2002T?  Because BQ2002T is one of customer's option.

Regards,

Koji Hamamoto

Hi Hamanoto-san
Good questions
1.) Resistor RB1, I recommend 10k to limit current and provide option if needed.
2.) The bq2002D and bq2002T have almost the same features. The T device has an additional feature to top-off charge using pulsed-trickle charge.
Thanks you for your patience in this matter.

Hi Bill-san,

Thank you! So BQ2002T will be possible to use as well. Is that correct?

Regards,
Koji Hamamoto