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LM74930-Q1: Polarity inversion protection + battery charger

Jimmy ROUX
Prodigy 40 points
Part Number: LM74930-Q1
Other Parts Discussed in Thread: LM74502H, , BQ21040, LM7480-Q1, LM74800-Q1

Tool/software:

Hi,

I am working on a new design powered by an INR18650 (3.7V) cell and I would like being able to achieve these two functions : 

- Protecting the circuit against polarity reverse as the cell will be removable

- Being able the charge the cell (from VOUT to VIN) from a USB port (over a BQ charger).

As far as I understand the LM74502H with common source MOSFETs should allows current to flow either from VIN to VOUT and from VOUT to VIN, so as long a cell is in place with the right polarity, it should be possible to charge it from VOUT..

Am I right ? Is it the good circuit to achieve this from your point of view ?

Thanks for your help

  • 0
    TI__Mastermind 48025 points

    Hi Jimmy,

    LM74502H can't be used as its minimum startup voltage is 3.9V and your cell is rated for 3.7V.

    LM74930-Q1 can be used here.

    Regards,

    Shiven Dhir

  • 0 in reply to Shiven Dhir
    Prodigy 40 points

    Hi Shiven,

    Thank you for your reply.

    Just to be sure, can you confirm that LM74930-Q1 can be used for dual direction current (using back to back mosfets) and so allowing to charge a battery (inr18650) with a charger such as BQ21040 ?

    Best 

    Jimmy

  • 0 in reply to Jimmy ROUX
    TI__Mastermind 48025 points

    Hi Jimmy,

    Yes, It can be used. Although it is important to note that startup needs to happen in forward direction first.

    By this I mean, battery should be plugged in, and controller should be on. After this MODE pin decides the flow of bidirectional current.

    Regards,

    Shiven Dhir

  • 0 in reply to Shiven Dhir
    Prodigy 40 points

    Hi Shiven,

    Again, thank you for your help.

    I noticed that the LM74930-Q1 is mentioned as 4V to 65V but also as 3V to 65V on the same page, can you confirm if 3V is correct ? : www.ti.com/.../LM74930-Q1

    Also I found the LM7480-Q1 which looks very interesting (simpler) as well for the same application. Can you confirm me if this also work (i see there is no mode pin on this one) ?

    Thanks a lot

    Best

    Jimmy

  • +1 in reply to Jimmy ROUX
    TI__Mastermind 48025 points

    Hi Jimmy,

    LM74800-Q1 will not support bidirectional current. You can disable unwanted features of LM74930-Q1 for easier implementation.

    LM74930-Q1 will work as far as VS>VS_PORR.

    Regards,

    Shiven Dhir

  • 0 in reply to Shiven Dhir
    Prodigy 40 points

    Dear Shiven,

    Ok very clear, thanks a lot for your help

    Best 

    Jimmy