BQ25723: Termination current of High current buck-boost charger

Hi Kuramochi-san,

Thanks for reaching out.

BQ25723/BQ25730/BQ25731 are all ICs to be used with a host processor as the charge current defaults to 0A.

With that assumption, the user can terminate charging anytime during the charging cycle using the processor.

From section 9.4.1.2 of the BQ25723 datasheet,

When battery is full or battery is not in good condition to charge, host terminates charge by setting CHRG_INHIBIT bit to 1b, or setting ChargeCurrent() to zero.

Thanks and I hope this helps,

Peng

*If my answer solves your question, please press "This Resolved My Issue" on the thread.  

Hello Peng-san,

Thank you for your support.

I think generic charger change current as following chart by themselves.

But, BQ25723/BQ25730/BQ25731 require to be controlled charge current by host MCU to achieve above charge current profile.
Is this understanding correct?

If above understanding correct, we can regard minimum charge current is termination current that is configured by charge current register.
All device's minimum charge current step seems 128mA because our customer need to support 10A or higher charge current.

Then, would you tell me charge current accuracy when we configured charge current as 128mA?
If it is better than +-50% the candidates can satisfy customer's requirement that is lower than 200mA.


Best regards,
Kazuki Kuramochi

Hi Kuramochi-san,

BQ25723/BQ25730/BQ25731 are smart chargers that need MCU intervention but they do implement the CC/CV profile. They just can't terminate by itself. Some of our other chargers will automatically terminate at a pre-set limit (termination current) in the constant voltage phase, but the ones mentioned in this thread does not.

After the charger enters the CV loop after the CC loop, charge current will begin tamper. The user then can terminate the charger at whatever charge current value they like.

Thanks and I hope this helps,

Peng

*If my answer solves your question, please press "This Resolved My Issue" on the thread.  

Hi Peng-san, 

I understand we need to control charging current manually for achieving battery charging profile.

Also, I asked charging current accuracy during minimum charging current case.(I think it is 128mA if we want to achieve 10A CC charge.)
Would you answer it?

Best regards,
Kazuki Kuramochi

Hi Kuramochi-san,

No, you do not need to control charging current manually to achieve battery charging profile. You just need to decide when to terminate.

After the charger enters the CV (constant voltage) loop after the CC (constant current) loop, charge current will begin to tamper. The user then can terminate the charger at whatever charge current value they like. For example, if you set the charge current to 1A, as it gets close to CV mode, the current will begin to tamper by itself as it gets close to regulation voltage. However, it will not really terminate at a certain charge current until the processor tells it to terminate.

The reason I didn't answer it was because it is not totally related to the customer question. In CV mode, the charge current register does not determine the charge current. When the current drops down to <200 mA (customer can measure this in anyway they want, usually the battery gauge/monitor have really high ADC accuracy), your customer can terminate the the charging.

Thanks and I hope this helps,

Peng

*If my answer solves your question, please press "This Resolved My Issue" on the thread.  

Hi Peng-san,

Thank you for correcting my miss understanding.

I understand that those device gradually regulate charge current during CV mode but we have to terminate the charging when charging current is reached at target current.

Then, would you tell me about the minimum charging current during CV mode from the viewpoint of device specification?
As I explained, they want to achieve charging current is lower than 200mA in CV mode.
I understood they need to terminate charging when charging current is reached this point but we'd like to know about whether this device can regulate charging current at lower than 200mA during CV mode including device variation.
Therefore I'm asking you about minimum charging current during CV mode.
We cannot distinguish that those device can satisfy their requirement from the point of view of device specification except this information.


Best regards,
Kazuki Kuramochi

Hi Kuramochi-san,

In CV mode, the device does not regulate current and only regulates voltage. When the charger is in CC mode, it regulates charging current and the value is set in the charge current register. When the charger is in CV mode, it does not regulate current and only regulates voltage. In other words, it does not and cannot control charging current in CV mode so your question is not valid.

You can think of it as a constant voltage source attached to a huge capacitor with some resistance (parasitic) in between. If you have a constant voltage source on a capacitor, it will source some current towards the cap initially but that current will gradually fall as the cap is charged up to the DC voltage of the source. The parasitic resistance between the capacitor and the DC voltage source will affect the current value during the process as well. You can run a simple simulation in SPICE.

In your case, you need to monitor that current and terminate it as it falls toward a certain value. BQ25723 has a 7 bit ADC that you can use, or they can use a battery gauge/monitor/protector (which they should have one in their system) with higher ADC resolution to monitor the current going through the battery.

Thanks and I hope this helps,

Peng

*If my answer solves your question, please press "This Resolved My Issue" on the thread.  

Hi Peng-san,

Sorry for my late reply.

I confirmed ADCICHG register's and this register's LSB is 64mA and 128mA.
So I think termination current will be 64mA or 128mA when we make the program that MCU terminate charging if this register's value reached at LSB.
Is this understanding correct?

If above understanding correct , I'd like to know about whether  there is any issue when I use above setting.
Would you tell me it?

Best regards,
Kazuki Kuramochi