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BQ24315: OVP recovery issue of BQ24315

Part Number: BQ24315

Hi,

I’m now evaluating BQ24315 OVP/OCP IC in my PCB board. So far, I’ve encountered a technical issue which I would like to share and seek advice (if any) as I still can’t figure out yet after round of experiments.

Please refer Figure 1 for simple block diagram (CH1 = power supply input (yellow), CH2 = VOUT from BQ24315 OVP/OCP IC (green), CH3 = /FAULT pin with pull up to 1.8V (red)) to illustrate circuit application.

Figure 1 – Original circuit application

In Figure 2, it presents all waveforms that I’ve captured so far. I’ve introduced an input voltage step change from 6V (OVP trigger at about 5.85V = VOVP) to 5V (expect output voltage recover immediately as usual).  As you may noticed, it’s obvious that output voltage (as well as /fault pin) suffers sort of undesired oscillation and take about 180ms to stabilize. It’s out of my expectation when I compare this behavior with respect to waveform presented inside BQ24315 IC datasheet.

Figure 2 – Waveform captured with original circuit application

After some troubleshooting, I found out that above-mentioned abnormal behavior will be resolved when I added extra 1ohm in between BQ24315 IC GND and power supply GND (refer Figure 3 for modified block diagram and Figure 4 for waveforms captured).

Figure 3 – Modified circuit application

 

Figure 4 – Waveform captured with modified circuit application

However, I still can’t figure out why additional 1R will help to solve undesired oscillation during input step change from 6V to 5V and what to cause such undesired oscillation.

Please kindly share your view in this matter, thank.

  • Hi KK,

    I am not sure what would cause this issue. Have you tried a different power source? I know that often a very stable supply is needed to test overvoltage thresholds because the sampling input might be causing a high voltage to be observed if the supply is not able to drive a stable voltage. 

    Best regards,

    Matt

  • Hi Matt,

         Thank to share view. In fact, I've tried 3 different power supplies before but then all behaves same as presented.

         Just curious, how to define stable power supply?

         Thank.

  • I was told by our validation team that a Kronhite supply is what they use for a stable source. They say when you are close to the protection threshold on a protector, the supply needs to hold a very stable voltage (like a battery cell would) to prevent false triggering.

    I am not sure if that is what you are seeing.

  • Hi Matt,   

         Did your team able to replica the issue based on unstable source as what I've observed at my lab?

    Also did you or your validation team able to figure out the reason why adding 1R will help to get rid of those undesired oscillation after OVP triggered?

    Just curious if it's ok to drive more than one LDO with Vout from BQ24315? Will it cause any potential issues?

    Thank.

    KK

  • Hi KK,

    This IC also has an input current protection threshold. Is there a chance you are hitting this threshold? That might explain why adding the resistor would make a difference.

    Best regards,

    Matt