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BQ77915: CURRENT LIMITER

Pankaj Yadav1
Prodigy 120 points
Part Number: BQ77915
Other Parts Discussed in Thread: BQ77905

Hi, I am designing 10S BMS and want to include Current Limiter Circuit of 5Amp, Please guide me if i can use CHG/DSG NMOS or i have to connect separate NMOS?

Where to connect Shunt resistance & how to power Gate?

I am using 

  • 0
    TI__Expert 7455 points

    Hi,

    To configure the current limiting feature, or OCD, you must adjust the value of the sense resistor Rsns. In this example, it is the 1mOhm resistor at the bottom of the diagram. To see an explanation of that calculation, refer to section 10.2.2.1 of the datasheet. Specifically, follow step 2. This fault will utilize the CHG and DSG pins and does not require any extra components.

     

  • 0 in reply to Shawn Hinkle
    Prodigy 120 points

    Our maximum continuous charging current is 5Amp

    Max. continuous charging current is 20Amp

    Discharge overcurrent protection: 60Amp

    I have not find any value of Rsns for above current conditions, so need your help Please suggest Solution...

  • 0 in reply to Pankaj Yadav1
    TI__Expert 7455 points

    Hi,

    To calculate the Rsns value, please follow the instructions in my previous post. 

  • 0 in reply to Shawn Hinkle
    Prodigy 120 points

    Hi, thanks for quick reply,

    Please check my prev. question again, both charge current & discharge currents are controlled by OCD1 and OCC by measuring voltage across Rsns.

    I am using 7791501, for this device fixed threshold values are 35mV for OCD1 and 20mV for OCC.

    I have calculated value of Rsns for Charging current of 5A as 4mohm, if i use  4mohm as Rsns resistance then discharge current is limited by OCD1 at 8.75Amp but we require approx 20Amp, this is problem i am facing....

    & Vice-versa(If i adjust Rsns value(1.75mohm) according to discharge current of 20Amp then this Rsns value is not suitable for limiting Charging current at 5Amp, as Rsns value of 1.75mohm provides charging FET cutoff at 11.43Amp.

    1. What is the solution for  above mentioned Problem?

    2. Can we change threshold values?

    3. Can we disable OCD1?

    4. Can we control Charging current by controlling CTRC Pin?

    5. Can we control charging current using Upper Device as i am designing 10S BMS which have two 7791501 IC's?

  • 0 in reply to Pankaj Yadav1
    TI__Expert 7455 points

    Hi,

    All of the current protections are configured by the Rsns. Therefore, you must choose one value. Typically, we choose the OCD1 value to determine the Rsns value.

    The voltage thresholds are fixed and cannot be reprogrammed. 

    You cannot disable OCD1 without disabling all of the current protections. 

    Yes, the charge current is controlled by the CTRC pin. It is a direct relay to the CHG pin. The CHG pin controls the charging current. 

  • 0 in reply to Shawn Hinkle
    Prodigy 120 points

    The answer is not Satisfactory, we need solution to limit both charging & discharging currents.

    One simple Question: Is this possible to limit Charging current at 5Amp and Discharging Current at 20Amp with this IC ? 

    If yes, then provide Solution.

    If not, can you(TI) provide IC's with threshold programmed as per our requirement ?

  • 0 in reply to Pankaj Yadav1
    TI__Expert 7455 points

    Hi,

    I have not gone through the calculations for every single one of our configurations, but it appears the BQ7791501 version would not fulfill this requirement. You would have to go through our devices and calculate the Rsns value needed for both OCD and OCC. If one of the configurations results in the same Rsns value for both protections, then it should meet your requirement. If cell balancing is not required, you may look at our BQ77905 configurations as well. 

    In most cases, you must choose one current fault to be higher priority and determine the Rsns value based on that.

    We make do make custom programmed configurations, but there is a minimum business case. If you wish to pursue that option, please contact your TI sales representative.