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BQ25895: bq25895 can't charger below 0℃ ambient

aggil liang
Expert 2660 points
Part Number: BQ25895

Hi Team

   We want to charge in  -20℃~60℃ range When we use BQ25895, and we design RT1=2.2k, RT2=6.5K, but it can't charge  below  0℃ ambient  when we test. The NTC datasheet is attachment. when we use 10k resistor instead of NTC, it can charge in  -20℃~60℃. 

  Pls.help to check where is wrong? NTC.pdf

  

  • 0
    TI__Guru**** 151085 points

    Aggil,

    What were your values for RT1 and RT2?  Using the spreadsheet calculator at  for the bq25895 TS Hot/Cold section and entering 2.51kohm for 60 C in the 45C field and 98.99kohm for -20C in the 0C filed, I compute RT1=2.24kohm and RT2=6.53kohm.

  • 0 in reply to Jeff F
    TI__Guru**** 151085 points
    Can you send me the register values while the device with NTC is charging correctly and then not charging?
  • 0 in reply to Jeff F
    Expert 2660 points

    Hi Jeff

         Figure 1 is register when the device with NTC is charging correctly and figure 2 is not charging . pls. help to check. 

         Another, what is the value of  VREGN when the VBUS is 5.6V input ? We test to find  that the value is equal to the VBUS. Is that right ?  But bq25895 datasheet is indicate the value of VREGN is 4.8V or 6V . 

  • 0 in reply to aggil liang
    TI__Guru**** 151085 points
    Aggil,

    Regarding not charging, the TS percentage per the ADC is 74.475%, which is above the V(LTF) battery cold spec. Therefore charge is disabled. I cannot explain why register 0C is reading 01, which is an invalid reading. It should read 0x05. Your software is reporting correctly that battery temperature is too low.

    Regarding the REGN voltage, REGN is the output of a linear regulator that is set to regulate to 5.6V - 6.4V. Like all linear regulators, this regulator requires its input voltage to be higher than its regulated output voltage by a certain dropout voltage. If not, the regulator runs in dropout where V(REGN) = V(PMID) - I(REGN) X Rdson(pass element).
  • 0 in reply to Jeff F
    TI__Guru 51361 points

    Since there's no further questions for a while, this thread is considered as solved.