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bq24271 current limit question

Matteo Geromin
Prodigy 200 points
Other Parts Discussed in Thread: BQ24271, BQ24270

Hi,

I'm going to desing a single cell Li-ion battery charger for a portable system with bq24271 charger.

My question is about conflicting information on datasheet.

on PIN FUNCTIONS description (pg9 SLUSB10) i found that PSEL pin is used to tell the charger the type of USB source and it consequently set currrent limit to 100mA or 1.5A, but in the "USB Input Current Limit Selector Input" section it tell that current limit is set on 500mA or 1.5A.

Now i want to know which information is correct.

thankYou in advance

Bye

Matteo Geromin

  • 0
    Guru 22270 points

    Hello Matteo,

    In this case, both statements are correct.  The two limits apply to DEFAUL mode and is determined by the following two conditions:

    1. In DEFAULT mode, the 500mA and 1.5A limit is set by a high and low value on PSEL.(BQ24271)

    2.  A D- and D+ adapter detection test is also performed in DEFAULT mode.  The result determines if the 100mA starting current is used and based on the conditions outlined on page 18, it will switch to the 1.5A limit. (BQ24270)

    Thanks,

  • 0 in reply to Greenja
    Prodigy 200 points

    ThankYou for the prompt response...

    bq24271 doesn't have D- D+ detection, but only has the PSEL pin, so I'm right to say that the current limits are 500mA and 1.5A for a low or high value on PSEL respectively?

  • 0 in reply to Matteo Geromin
    Guru 22270 points

    Yes, according to the specs you are correct.  

    I will have to edit my previous post to include the distinction between the devices as outlined in the data sheet.

    Thanks,

  • 0 in reply to Greenja
    Intellectual 910 points

    Hi Guys,

    Have you accessed these device via I2C for you applications.

    The datasheet doesn't explain the I2C protocol fully so I'd like to hear how people have sucessfully read or written the registers.

    My assumption at the moment is the the MASTER processor just sends the address (with R/W), and then clock 8 bytes of data. If this is the case it means I can't just write a single register. Some devices utilise the first byte written as an address to select the register. Again, the datasheet does not make this operation clear or provide any examples.

    Any help much appreciated as I am struggling with this device, seems todo the 50mA initial charge and then stop.

  • 0 in reply to Rob Weekly
    Prodigy 200 points

    Hi,

    I don't had any problem with the I2C interface, as I just read or write to the device registers as any other devices. The first transaction is the 7bits device address with RW bit, the second 8bits identify the register to access and the third is the data from the device in case of a read or the data to be written to the register.

    You must pay attention to the watchdog timer. The first time you make an I2C access to this device a 30seconds watchdog starts. It must be cleared before 30seconds otherwise the charger sets the DEFAULT mode, putting all registers to default values.

    I hope i've helped you

    Bye

    Matteo Geromin

  • 0 in reply to Matteo Geromin
    Intellectual 910 points

    Hi Matteo,

    Thanks for the info.

    Can you also confirm if

    a) the register address auto increments. (Thus you can read 3 adjacent registers in a single access).

    b) if you set the address as '1' then didi 8 reads, would the address wrap around?

    Best Regards

    Rob

  • 0 in reply to Rob Weekly
    Prodigy 200 points

    It seems that the BQ24271 doesn't have the address auto-increment functionality