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Part Number: BQ25619
How can I adjust the system voltage of the buck. I just found the upper and lower limits in the datasheet but not how to adjust the system voltage it self. I would like to have a system voltage not higher than 3.6 volts.
You can set the minimum system voltage when the battery is discharged using REG01b[0:3]. Default is 3.5V. However, after the battery charges higher than 3.5V, V(SYS) follows V(BAT) up to the battery regulation voltage + ~150mV. So, when the battery is fully charged, V(SYS)=4.2V+150mV = 4.35V. This is how all of our power path chargers function. If you need a lower system voltage, then I suggest adding a buck converter with 100% duty cycle following V(SYS).
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In reply to Jeff F:
In reply to Raphael Jambor:
If using a LiFePO battery, I recommend that you start the charger with /CE pin = high, With /CE pin=high, the SYS output will initially regulate to MINSYS=3.6V. Then use I2C to change the VBATREG register = 3.6V and the MINSYS voltage register to something lower than 3.6V like 3.3V. The I2C settings will stay assuming you periodically write to the watchdog timer bit or disable watchdog timer, unless the charger is completely powered down. Then you can use your host GPIO to pull /CE pin low for LiFePo charging.
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