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BQ78350-R1: LEDs permanently lit

Bernhard Suppan
Prodigy 230 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350

I am developing my own PCB. Instead of using one transistor as on the EVM board, I used resistors for each LED.
They are now permanently lightning, but if I send the LED toogle command, they light a bit brighter.

One LED is connected to VC10 (24V) an to one resistor (8450R). The resistor is connected to one led pin of bq78350-r1.


What could be the cause?

  • 0
    TI__Guru 54715 points
    Hi Bernhard,
    The abs max voltage of the LED outputs of the bq78350 is 6V with the recommendation not to exceed VCC which is 2.5V nominal. Likely the LEDs and series resistor are pulling up the LED outputs which are leaking current to either GND or VCC causing the LEDs to light. When the LED outputs are turned on they will sink 3mA, if this makes the LEDs brighter the leakage when off must be lower. You will need a supply for the LEDs somewhere between VCC and VCC+ Vf of the LEDs, something in the 3V to 3.3V range is probably good. REGOUT from the bq769x0 may not be able to provide sufficient current for both the gauge during flash update and the LEDs if both were on simultaneously, the transistor on the EVM was a simple low part count method.