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bq24075 not charging, new user

pixbroker
Genius 5820 points
Other Parts Discussed in Thread: BQ24075

Hello,

im new to bq24075 and just assembled the first prototype and the charger is not charging, so i assume i interpreted the data sheet wrong. 

i have attached my schematic. the interesting thing is that both CHG and PGOOD do in fact go low when i connect the USB power, and go back up high when i disconnect, however, when they are low, one would assume the charger is charging but it's actually not (considering the input current is near zero). im using BQ24075RGTT btw.

also, fi the battery is full, one would expect CHG to ho high again, at some point, which it is not, ever.

i must have made some basic mistake in designing my circuit and i kindly ask someone familiar with the device to take a look.

thank you very much.

  • 0
    Mastermind 7395 points

    Hi,

    Are the resistors for Iset and Ilim really not placed? They should be

    I didnt understand the connection of TS, it should be a single10K resistor to GND.

  • 0 in reply to Avi Chami1
    Genius 5820 points

    Thanks for the quick response. 

    As to Iset and Ilim, i had originally thought that if i use EN1 and EN2 to force USB100 mode, those resistors become dontcare. but after there was no charge, i actually placed them but that didn't change anything. 

    The TD pin in my schematic is a bit misleading, i apologize. Since i have the BQ24075 part, this is really SYSOFF. My understanding was that this should connect to GND if not used. Could that be the issue?

    As to TS, the datasheet states:

    For applications that do not require the TS monitoring function, set R6 = 200kΩ and R7 = 49.9kΩ to set the TS voltage at a valid level and maintain charging. 


    and my schematic implements that.

    UPDATE: Avi, thank you very much, indeed the TS was the problem. I placed a 10k to GND as per your suggestion and now charging at 100mA as expected. Very confusing why the data sheet states the voltage divider should be used. 

    But now i have another question: when using EN1 and EN2 to select USB100 or USB500 mode, what should the values for Iset and Ilim be? are they even relevant?

    Thanks again

  • 0 in reply to pixbroker
    Mastermind 7395 points

    En1 and En2 only dictate the current limit, you still need Iset.