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BQ25751: BQ25751 and 4 MOSFET were easily damaged under boost charging mode

Lesheng Cao
Prodigy 110 points
Part Number: BQ25751

Tool/software:

Hi,

I used BQ25751 for lead acid battery charging/ power path management prototype board, the nominal input voltage is 48Vdc, the charging voltage is set for 56VDC, during testing and debugging, I found the BQ25751&MOSFET were very easily damaged with a very small charging current load like 500mA.

1,Both external power supply and lead-acid battery can supply the system individually, but if I started to charge the battery by enable "charging" conditions like by plugging the temperature sensor and set the charging current to 500mA, the IC will be damaged.

2,I changed the resistor to ensure it can work within the input voltage range(12V-50V), and also changed the FB resistor to make it work as a buck battery charger, I set the external power supply to 36V, the charge voltage to 30V,we found the BQ25751 can charge the battery (reduce the number of battery cells at the same time) with different charging current.

3,I set the external DC power supply to 18V and changed the FB resistor to make it work as a boost battery charger, set the charge voltage to 27V, the BQ25751 can charging the battery with different charging current.

But if I set the charging voltage to 56V ( and set the external power supply to 48V ), the BQ25751 and MOSFETs will be damaged very easily.

I attached schematics and data log captured on damaged board for your reference.

Thanks

Kelvin

Battery register address 0   Register value: 0x10 
 Battery register address 0x1   Register value: 0 
 Battery register address 0x2   Register value: 0x40 
 Battery register address 0x3   Register value: 0x6 
 Battery register address 0x6   Register value: 0x40 
 Battery register address 0x7   Register value: 0x6 
 Battery register address 0x8   Register value: 0xd0 
 Battery register address 0x9   Register value: 0x20 
 Battery register address 0xa   Register value: 0x40 
 Battery register address 0xb   Register value: 0x6 
 Battery register address 0xc   Register value: 0xe8 
 Battery register address 0xd   Register value: 0x3 
 Battery register address 0x12   Register value: 0xa0 
 Battery register address 0x13   Register value: 0 
 Battery register address 0x14   Register value: 0x8 
 Battery register address 0x15   Register value: 0x30 
 Battery register address 0x16   Register value: 0xd3 
 Battery register address 0x17   Register value: 0x9 
 Battery register address 0x18   Register value: 0xc0 
 Battery register address 0x19   Register value: 0x4 
 Battery register address 0x1a   Register value: 0x20 
 Battery register address 0x1b   Register value: 0x80 
 Battery register address 0x1c   Register value: 0x81 
 Battery register address 0x1d   Register value: 0x40 
 Battery register address 0x1e   Register value: 0 
 Battery register address 0x1f   Register value: 0 
 Battery register address 0x20   Register value: 0 
 Battery register address 0x21   Register value: 0 
 Battery register address 0x22   Register value: 0x80 
 Battery register address 0x23   Register value: 0x2 
 Battery register address 0x24   Register value: 0x2 
 Battery register address 0x25   Register value: 0 
 Battery register address 0x26   Register value: 0 
 Battery register address 0x27   Register value: 0 
 Battery register address 0x28   Register value: 0 
 Battery register address 0x29   Register value: 0 
 Battery register address 0x2a   Register value: 0 
 Battery register address 0x2b   Register value: 0x8c 
 Battery register address 0x2c   Register value: 0x2 
 Battery register address 0x2d   Register value: 0x45 
 Battery register address 0x2f   Register value: 0 
 Battery register address 0x30   Register value: 0 
 Battery register address 0x31   Register value: 0xe8 
 Battery register address 0x32   Register value: 0x5c 
 Battery register address 0x33   Register value: 0 
 Battery register address 0x34   Register value: 0 
 Battery register address 0x35   Register value: 0x69 
 Battery register address 0x36   Register value: 0x5d 
 Battery register address 0x37   Register value: 0 
 Battery register address 0x38   Register value: 0 
 Battery register address 0x39   Register value: 0 
 Battery register address 0x3a   Register value: 0 
 Battery register address 0x3b   Register value: 0 
 Battery register address 0x3c   Register value: 0 
 Battery register address 0x3d   Register value: 0xa 
 Battery register address 0x62   Register value: 0x2 
  • 0
    Prodigy 110 points

    The MOSFET we used is BSC340N08NS3-G, the Vds is 80V, it is different with the MOSFET used on TI demo board, on TI demo board the Vds of mosfet is 100V

  • 0 in reply to Lesheng Cao
    TI__Mastermind 31246 points

    Hello Lesheng,

    Have you tried testing this on an EVM?

    Have you tried using the FETS that are on the EVM?

    Best Regards,

    Christian

  • 0 in reply to Christian Moyer
    Prodigy 110 points

    Hi Christian,

    The MOSFET we used is different with EVM board, we used BSC340N08NS3-G from Infinion, the Vds is 80V, however the Vds of mosfet used on EVM is 100V.

    The EVM was designed not support to work with 56V battery charger, I have to do some hand work modification.

    Thanks

  • 0 in reply to Christian Moyer
    Prodigy 110 points

    Hi Christian,

    The MOSFET we used is different with EVM board, we used BSC340N08NS3-G from Infinion, the Vds is 80V, however the Vds of mosfet used on EVM is 100V.

    The EVM was designed not support to work with 56V battery charger, I have to do some hand work modification.

    Thanks

  • 0 in reply to Christian Moyer
    Prodigy 110 points

    I set the e-load to CC mode and connected to the board, after I power up the board with an external DC power supply 48V, at the beginning I can see the charge voltage is 56V, but after a few second the charging voltage is disappear( actually at this time I still didn’t turn on the e-load, the key of ON/OFF of e-load is off, the current is 0),  the BQ25751 was damaged. And the stat1,stat2 LEDs are ON indicated “charging fault detected”, I measured the REGN pin of BQ25751, the REGN LDO inside of BQ25751 output is not 5V anymore, it is zero ( on some other damaged board, the REGN LDO output is about 1.2V).

     

    I modified the EVM board to set the charging voltage to 56V and did the same test on EVM board by setting the e-load in CC mode, it works fine on EVM board.

  • 0 in reply to Christian Moyer
    Prodigy 110 points

    I found the chip BQ25751 we used is different with the chip used on EVM board, on EVM board it is BQ2575X, not BQ25751 we used.

  • 0 in reply to Lesheng Cao
    TI__Mastermind 31246 points

    Hello Lesheng,

    Lesheng Cao said:
    I found the chip BQ25751 we used is different with the chip used on EVM board, on EVM board it is BQ2575X, not BQ25751 we used.

    The IC on the EVM should be BQ25751, it may be from a different batch that has a different top marking.

    Lesheng Cao said:
    I set the e-load to CC mode and connected to the board,

    The E-load should be in CV mode, and you will set the current that it draws in the ICHG_REG. I highly recommend using a 2000µF of capacitance across the VBAT.

    Best Regards,

    Christian.