BQ76920: Getting unexpected OVRD_ALERT status

Scott Nelson

Part Number: BQ76920

I have nothing connected to the ALERT pin except a 1M pulldown and a 1K series resistor to an empty pin header. After clearing all the status bits (when resetting the host MCU) I immediately see an OVRD_ALERT status along with 2.5V present at the ALERT pin. I was not having this issue yesterday and I have not changed anything. Any ideas about what could be causing this?

over 6 years ago

0 Vish Nadarajah over 6 years ago

TI__Expert 6085 points

OVRD_ALERT bit is being set due to fact there is some residual voltage on the ALERT Pin. 2.5V voltage on ALERT is a solid logic high. ALERT pin response could be due to a spurious glitch coupling onto the ALERT pin.

(1) take out the 1K series resistor.

(2) change out the 1Mohm to ~500K to GND. Also add a 470pF cap to GND.

(3) make certain, the SYS_CTRL registers are cleared. to CLEAR write "1" in the corresponding register.

hope this helps out.

0 Scott Nelson over 6 years ago in reply to Vish Nadarajah

Intellectual 340 points

OK, now there's a 500K resistor from the ALERT pin straight to ground (nothing else). I'm still seeing a steady 2.5V on that pin and the OVRD_ALERT status being triggered accordingly.

0 Scott Nelson over 6 years ago in reply to Scott Nelson

Intellectual 340 points

Is there anything else (aside from spurious voltage spikes on the ALERT line) that could cause this issue?

0 Scott Nelson over 6 years ago in reply to Scott Nelson

Intellectual 340 points

Replacing the pull down with 160k seems to be working.

0 Scott Nelson over 6 years ago in reply to Scott Nelson

Intellectual 340 points

I spoke too soon. Even with a 160k pulldown on the ALERT pin I'm still seeing a steady logic high and the OVRD_ALERT bit set in SYS_STAT. It was fine for a while and now I cannot seem to clear OVRD_ALERT.

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BQ76920: Getting unexpected OVRD_ALERT status