• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 464 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ77915: Charge mosfet don't turn on.

Ahmet Burma
Prodigy 80 points
Part Number: BQ77915

Hi everyone.

I want to design simple and cheap battery protection circuit for 4 serial cell. I will not use over current and over temperature protection. In this reason, i am using "BQ7791504PW". Discharge mosfet and under voltage protection is working good. But charge mosfet dont turn on and I cant charge battery. The schematic is below. I designed the schematic with the current protection circuit, but I will not use it.

  • 0
    TI__Genius 11315 points

    Hey Ahmet,

    Can you measure the voltages at the gates of the CHG and DSG FETs? Your schematic looks okay, so I'm wondering if any other protections are being triggered.

    Thanks,
    Caleb

  • +1 in reply to Caleb Perez
    Prodigy 80 points

    Hi Caleb,

    Charge pin voltage is 1.6V, discharge pin voltage is 1.6V, CHG mosfet gate voltage is 0.6V and DSG mosfet gate voltage is 1.6V in no load condition. When i connect a few amps load to the battery, charge pin voltage is 2.2V, discharge pin voltage is 2.2V, CHG mosfet gate voltage is 1.6V and DSG mosfet gate voltage is 2.2V.

    Edit: I found the problem. To summarize, when I first started to try the circuit, I connected a 2 amp resistor load to the battery terminals and ran it. But the mosfets got extremely hot. The internal resistance of the mosfets I use is 1mR and it is not possible for them to heat up with such a low load. The very low gate voltages and the unstable operation of the circuit from time to time led me to control the components. And bingo :). R1 and R17 resistors are assembled incorrectly. R1 = 3MR and R17 = 1K. Therefore BQ77915 was operating at very low currents about 5uA. Now everything works normally (charge and discharge). 

    Thanks for your time Caleb. 

    Have a nice day.