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Inquiry about battery protection circuit

MJ Jeon
Genius 5240 points
Other Parts Discussed in Thread: BQ2980, BQ27Z746

Hi, TI support team

I have received inquiries about the battery pack protection circuit applied to tablets from our customers.

[Battery]

- 10000mAh * 2 (parallel connection)

- 10000mAh * 3 (parallel connection)

Q1. Should batteries connected in parallel have a protection circuit (PCM) applied to each cell?

Or should the protection circuit for the entire connected battery be applied?

(If you have a product that meets the above battery specifications, please let us know.)

Q2. If connected in parallel, should I use a cell balacing IC?

(If you have a product that meets the above battery specifications, please let us know.)

Thanks.

Regards,

MJ

  • 0
    Genius 5240 points

    Hi, TI support team

    Regarding the inquiries received from customers, we would like to ask you additionally as follows.

    1) Battery usage environment (existing)

    - Use of a large-capacity power bank to extend usage time in a restaurant menu board tablet environment

    - Commercially available USB 2.0 high-capacity battery

    (1) 20,000mAh = 10,000mAh 2cell parallel

    (2) 30,000mAh = 10,000mAh 3Cell in parallel

    => Problems with auxiliary batteries: Unable to manage remaining battery life, battery life, etc. in USB charging state

    Shortening of life span or swelling due to cell balancing problems, risk of fire in large-capacity cells

    2) Large-capacity auxiliary battery -> Large-capacity main battery (removable): under development

    - By directly attaching a large-capacity cell to the main battery, the OS requires remote management of battery life, charging and discharging, and on/off

    - Prevention of overcharge, overdischarge, and fire risk by adding PCM and BMS suitable for large-capacity cell

    - Problem: No experience in applying BMS and PCM circuits due to parallel connection of large-capacity cells

    Q1) Is the individual PCM circuit effective if two or three of the above PCM-attached batteries are attached in parallel?

    Q2) Is there a BMS IC or circuit that can manage up to 3 cells with PCM attached?

    Q3) What is the minimum battery cell management method in the following parallel situation?

    Thanks.

    Regards,

    MJ

  • 0 in reply to MJ Jeon
    TI__Expert 3245 points

    Hi MJ, 

    Please see responses to the questions. 

    MJ Jeon said:
    Q1) Is the individual PCM circuit effective if two or three of the above PCM-attached batteries are attached in parallel?

    A1.) Yes a protector IC should be sufficient for your cell configurations (1s2p or 1s3p).

    MJ Jeon said:
    Q2) Is there a BMS IC or circuit that can manage up to 3 cells with PCM attached?

    A2.) For these 1s2p and 1s3p configurations only a single-cell protector would be applicable here. In this case that is the BQ297x and the BQ298x protectors, both have primary protection features like OV, UV, OCC, OCD,  and OT protections. These protectors include low-side FET drivers for the BQ297x and high-side FET driver for the BQ2980 which will include a charge pump to ensure sufficient gate voltage at the FET for high-side configurations. 

    MJ Jeon said:
    Q3) What is the minimum battery cell management method in the following parallel situation?

    A3.) I am not sure what is meant by the question. If we have a scenario where 1s3p configuration has a bad cell, then the protector IC will see the same voltage since they are all in parallel. The protector will then only take action when an protection event is seen such as an OVP or UVP event for example. The protection IC can then drive a FET or fuse to disconnect the pack. 

    Please see the simplified schematic for a better idea on implementation for 1s3p case. 

    To further clarify, our protector will only be looking at voltage to make decisions. So in the case where you have 1s3p where one cell has far less capacity than the other, the protector will not be able to detect a capacity change.

    If you require such a feature this may be more suited for a gauge IC such as the BQ27Z746 which lives in the battery pack. While this gauge will not be able to determine which specific cell has degraded in a parallel configuration, it will be able to detect that the overall pack capacity has decreased so action may be taken. 

    While I am sure there are other useful features of the BQ27Z746, I am not proficient with this gauge. With that said,  I would suggest you start a new thread if you have follow up questions on the BQ27Z746 so it may be assigned to the correct expert. 

    Best, 

    -Luis Torres