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bq24250 and bq24250C

Other Parts Discussed in Thread: BQ24250C, BQ24250


           I have doubts about the behaviour of bq24250 and bq24250C:


1.- If I put /CE pin HIGH the charge is disabled. I want to put this pin to a fixed HIGH level and start charging only via I2C. The idea is that the charging is disabled at power up and the only way to start charging will be via I2C. I think this will work, but what happens if the watchdog timer expires? The datasheet states that if watchdog timer expires the charger will enter DEFAULT mode, so when enters this mode, the charge will be disabled again? 


1.- This charger has a modified JEITA charging profile. I want to fix the Thot  temperature to 45 celsius degrees instead of 60. If I modify this temperature to 45C, the Tcool wil be modified as well. This is not a problem, because for me it is better if  Tcool is closer to the standard JEITA (about 10C). With a 10k NTC resistor and beta close to 3500K, Tcool is about 17.5C. This works well for me, but I want to know if I can do this modification and that it will not cause any problem. 

                        Thank you in advance.

  • Regarding 250 question, disabling charge, whether with /CE pin or bit, also takes precedence.  So, if /CE pin is HIGH, you cannot start charging via I2C.

    Regarding 250C, you can choose the TS resistors to set the HOT and COLD temperature thresholds where you want, but as you note, the COOL and WARM thresholds will change.  As long as the HOT and COLD set points are consistent with what your battery manufacturer recommends, I see no issue.

  • Hello Jeff.
    Thanks for your help. More questions:
    1.- If /CE pin is always LOW, could I start and stop the charge via I2C?
    2.- If EN1 and EN2 are always a fixed combination (say EN1= 1 and EN2 = 0, for example) tying these pins to VIn and GND respectively, an then the charger enters HOST mode after a I2C command, what will be the input current limit? I ask this question because the bits in the I2C register that set this parameter are XXX in reset state and I am not sure what this means.
    3.- If the watchdog timer expires, the input current limit and fast charge current will be set by EN1-EN2 and ISET as before to enter HOST mode?

    Thank you in advance.
  • Regarding 1, yes.
    Regarding 2 and 3, EN set the ILIM when not in HOST mode (i.e., if watchdog timer has not expired). Once in HOST mode the registers determine ILIM.
  • Hello.
    Thanks. Say that the charger is in HOST mode, but for whatever reason, I2C communications fail and the uC can not communicate with the charger and therefore the watchdog timer could not be reset via an I2C command. Say too that EN1-EN2 are at a fixed level, for example EN1=1 and EN2=0:

    1.- When the watchdog expires, the limit current will be again set by EN1 and EN2 and the charge current will be set by the value of the resistor attached to ILIM pin?
  • Hello Jeff.
    Thank you again for your help. I have more questions:

    1.- In the description of the pin ISET in the datasheet states that the charge current is programmable from 300mA to 2A. Is not possible to program a current of, for example 100 mA with the external resistor?

    2.- In the description of the Register #5, states:
    B5 -> LOW_CHG -> 1:Low charge current setting 330 mA.
    What I understand is that if this bit is 1, the charge current will be 330mA, but if you read the bit description under the table, states:
    LOW_CHG -> When set to 1, the charge current is reduced 330mA...

    So, the charge current will be 330mA or will be reduced 330mA (if it´s 1A, for example, will be 1000-330=670 mA)?
  • Regarding 1, we do not production test below the value stated in the datasheet but we have other customers who have set 100mA with ISET without any issues. The charge current and (termination current in standalone mode) accuracy will be worse.
    Regarding 2, charge current = 330mA when LOW_CHG=1.
  • Hello Jeff. Thank you.
    More questions:
    1.- Can I set the charging current via ISET pin to a very low current (1 mA or so)? I am not going to charge at this current, but I want to add this extra security feature: If communications via I2C are not working, the charger will enter DEFAULT mode and the charging current will be only 1 mA, because I do not want the charger to charge the battery if there is no communication with the HOST uC or the HOST is damaged.
  • Although this should theoretically work, we do not test with low of charge current so I cannot provide any warranty. A better way might be to use one of the HOST's GPIO to control the /CE pin. If host is available, then /CE is pulled low if not it is pulled to IN.
  • Hello. Thank you for your help.

    Which is the minimum current I can program using ISET pin? You said that 100mA is a valid current as some customers use it, so which is the smallest current?