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BQ24157: bq24157 low charge

Hollis Liu
Intellectual 2595 points
Part Number: BQ24157
Other Parts Discussed in Thread: BQ25100

Hi Team, 

Can i know how to use low charge mode of BQ24157? What scenario we will use low charge mode in? 

What's the recommended setup to limit the max charge current to be 160mA? Thanks. 

  • 0
    TI__Guru**** 164656 points

    Hi Hollis,

    Low charge was helpful with legacy USB ports that could only provide 500mA and below before USB enumeration.  Now it is rarely used.

    Although we have not tested resistors higher than those in the datasheet and GUI, you can use a larger external SNS resistor to set the maximum charge current to essentially whatever value you want. 

    The BQ24157 with such low charge current will be very inefficient.  You might consider changing to a linear charger like BQ25100.

    Regards,

    Jeff  

  • 0 in reply to Jeff F
    TI__Intellectual 2595 points

    Hi Jeff,

    thanks for your feedback. I see bq25100 price is higher than bq24157 and the charge efficiency is also lower than bq24157. 

    I am thinking to set Iin_limit to 100mA. Then the charge current can be limited to around 160mA. Is there any potential risk? 

    B7 (MSB) Iin_Limit_2 Read/Write 00-USB host with 100-mA current limit, 01-USB host with 500-mA current limit, 10-
    USB host/charger with 800-mA current limit, 11-No input current limit
    B6 Iin_Limit_1 Read/Write




  • 0 in reply to Hollis Liu
    TI__Guru**** 164656 points

    Hi Hollis,

    Yes, you can limit charger input current which will limit charge current. 

    Regards,

    Jeff

  • 0 in reply to Hollis Liu
    TI__Intellectual 2595 points

    Or i set low charge mode=1 and set the Rsns=140mohm to set  160mA charge current.

    if low charge mode=1, do that mean i am using special charge voltage?

    if Rsns=140mohm, the min charge limit which is set by 0x06 is 37.4/140mohm=267mA, right?

  • 0 in reply to Hollis Liu
    TI__Guru**** 164656 points

    Hi Hollis,

    Special charge voltage is VINDPM (regulates charger input voltage by lowering charge current to prevent input crash)  and is separate from low charge mode.

    With RSNS = 140mohm and low charge mode = 0, Ichargmin= 37.4mV/140mohm=267mA.

    With RSNS = 140mohm and low charge mode = 1, Ichargmin= 22.1mV/140mohm=158mA.

    Regards,

    Jeff