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BQ24070: never end precharge and low charge current

Robin Galipeau
Prodigy 40 points
Part Number: BQ24070

I have used the part value of the Detailed Design Procedure at the page 21 of the datasheett. 

Mode, ISET2 and CE are HIGH with a 6volt 5A source at input.

The data sheet exemple resistor value should get a 1A charge current. But actually whe I plug a batterie with 4.03V ISET1 and ISET2 LEDs are on which represent precharge state.

also accordly to the exemple, the precharge curent is 100mA but in my case the charge current is 500mA.

I really don't know what is going on.

Please help me :) 

  • 0
    TI__Mastermind 21590 points
    Hello Robin,
    Can you please post your schematic.
  • 0 in reply to Robin Galipeau
    TI__Mastermind 21590 points
    Robin,
    Can you measure the Voltage on Mode and ISET2?
  • 0 in reply to Raheem
    Prodigy 40 points
    Hi,
    The voltage is 4.4 (I pull up those pins with vout)

    mean while I tesed thecircuit a little bit more and I discovered with my osciloscope that Stat1 and 2 where oscillating whith a frequency of 60Hz.
    I changed the Rdppm for a 20K and the oscillation disapered. Also the charging current had augmented. And the chip died.

    I have soldered a new one, I tested each lead and there is no short. I power up the circuit and it finally charge the battery at 1A, and the Stat led show the right status. But after aproximately one minute, the current increase to 1.5 A (there is no load on the output).
    I shut off the circuit and discovered that there is now a short to ground on the Vref pin. If I heat up the chip the short goes away for a short time.

    I do not kown what can cause this, before the first power up there was no short circuit.

    thank you.
  • 0 in reply to Robin Galipeau
    TI__Mastermind 21590 points
    Hello Robin,
    The VDDPM voltage should be between 3 and 4.3V. Setting RDPPM to 37.5k put it close to the max dppm voltage and 20K places the DPPM voltage at 2.3V. Please set RDPPM to 30K ohms and check to see if this solves your issue.
  • 0 in reply to Raheem
    Prodigy 40 points
    Hi, Raheem,

    Using a 30K ohm RDPPM resistor resolve my issue.

    Thank you very much!!!

    Could you explain me why setting a too high or low value of RDPPM destroy the chip. I think I miss something in the datasheet about the dppm feature. I though It only decrease the charging current to allow a higher ouptut current in case of a load .

    Thank you again :)
  • 0 in reply to Robin Galipeau
    TI__Mastermind 21590 points
    Robin,
    The device output is regulated to 4.4V. Setting the DPPM voltage higher than 4.4V will reduce the charge current due to the device always being in DPPM mode. Also you would be operating the device outside the parameters stated in the datasheet.