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BQ24075: BQ24075RGTR Charge protection time

liu billy
Intellectual 590 points
Part Number: BQ24075
Other Parts Discussed in Thread: BQ24072

Tool/software:

hi  

  Test charge protection time  about BQ24072. The external power supply at the battery end is 3.8V, and the USB end is 5V. The battery is only connected to the NTC and GND to ensure the normal operation of the charge IC

The definition here is the Charge safety timer and the definition is 4-6H.  but 
I tested it a little off spec, 6.04H. What could be the cause?      

   Q2 :QON PIN   external Gnd, can always be in a LOW state, or will there be any impact   ?  

  Q3:I connect a capacitor to the PIN of TMR. If the capacitor is not full at the moment of power-on, will it short circuit, which will cause the timer to fail all the time?

  • 0
    TI__Mastermind 31840 points

    Hi Liu, 

    Thank you for reaching out via E2E. Please see my comments below. 

    1) For your charge safety timer test is the TMR pin left unconnected? If not what is the resistor value between TMR and GND? Additionally was charge current constant at your set ICHG value throughout the test? I ask because charge safety timer is slowed down if at any time the device reaches the input current limit. 

    2) Can you please double check which charger IC you are referring to for Q2? The BQ24072 does not have a QON pin. 

    3) Please do not connect a capacitor to TMR pin. There should only be a resistor to GND with a value in range of 18kohm to 72kohm at TMR or pin should be left floating to set safety timer to default length. The capacitor at TMR may be impacting the result of your safety timer test. I recommend you repeat with the capacitor removed. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Intellectual 590 points

    hi  Garrett

       I removed the capacitance test. Time was 6H,  It  reached the ceiling . Is there any other reason that will affect the charge protection time

  • 0 in reply to liu billy
    TI__Mastermind 31840 points

    Hi Liu, 

    To further debug please help to answer my questions from my previous reply. I have restated most critical open questions below.

    -In the new test is TMR pin left floating? 

    -What is input current limit and charge current settings in the test and have you verified charge current remains constant throughout the test? 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 30 points

    Hi Garrett
         new test is TMR pin left floating, input current limit is 0.5A. charge current  in the test is 472mA. See the following figure,when 6H,charge current down.

    datasheet about safty time limit max is 6H. It  reached the ceiling . Is there any other reason that will affect the charge protection time?

  • 0 in reply to Huang YQ
    TI__Mastermind 31840 points

    Hello, 

    Please see my comments below. 

    Huang YQ said:
    See the following figure,when 6H,charge current down.

    Are you stating the device stops charge or you are stopping charge? If the device is stopping charge current on its own then the safety timer appears to be working as intended. 

    Huang YQ said:
    Is there any other reason that will affect the charge protection time?

    All events which increase safety timer duration are listed in datasheet section 9.3.5.6. The same section also describes actions which will result in safety timer being reset. To summarize events which lead to extended safety timer are as follows:

    1) DPPM loop activated due to reaching input current limit,

    2)Charge current limited due to input voltage falling to Vin-dpm

    3)device in thermal regulation

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 30 points

    Hi Garrett：

         the device stops charge,thank you for your reply.

    Garrett Kreger said:
    Are you stating the device stops charge or you are stopping charge? If the device is stopping charge current on its own then the safety timer appears to be working as intended. 
  • 0 in reply to Garrett Kreger
    Prodigy 30 points

    Hi Garrett:

         I have one more question,these event effcets safety timer,maybe out of range 6H? beyond specification definition 6H?

    1) DPPM loop activated due to reaching input current limit,

    2)Charge current limited due to input voltage falling to Vin-dpm

    3)device in thermal regulation

  • 0 in reply to Huang YQ
    TI__Mastermind 31840 points

    Hello, 

    The three events you list will all cause safety timer to count at half speed as long as they are present and therefore extend overall safety timer length. Any of those 3 events could cause safety timer to become longer than the 6 hour specification. 

    Best Regards

    Garrett