PF8200: VIN spikes when shutting down

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PF8200: VIN spikes when shutting down

491 Views
adevries
Contributor V

Hello NXP Forum,

I posted a question on this topic previously, but I am posting again in hopes to learn some new information. 

When commanded to reboot, the PF8200 will backfeed current into VIN, causing the voltage at VIN to spike unless the voltage source powering the PF8200 can sink enough current. This behavior is mentioned in the PF8200 datasheet, in a note on Table 9: "Input supply for switching regulators must be capable to sink current to avoid overvoltage condition during the power down sequence of the device".

I am designing a product that has a switched-mode power supply creating 5VDC, which I am feeding into the PF8200. Apparently, the power supply isn't able to sink enough current, because every time the PMIC is commanded to reset power, I'm seeing VIN spike up to 5.5V (see attached image). This is very concerning, because the operating range of the PF8200 is only up to 5.5V, so I'm worried this spike will break the PMIC.

Can someone please explain the mechanism behind this behavior? And offer some ideas for how I can limit this voltage spike? If I have a better understanding of what's going on, I'm hoping I can better control this backfeeding so I don't have to switch PMIC's.

 

Thanks

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8 Replies

460 Views
guoweisun
NXP TechSupport
NXP TechSupport

I will escalate this case to app support team,please wait for response!

 

435 Views
adevries
Contributor V

Hi @guoweisun,

 

Has app support been able to reproduce this issue? Can they provide any insight on this problem?

 

Thanks

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430 Views
guoweisun
NXP TechSupport
NXP TechSupport

Still in progress.

 

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420 Views
adevries
Contributor V

Hi @guoweisun,

Has there been any progress on this request for support?

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413 Views
guoweisun
NXP TechSupport
NXP TechSupport

If read datasheet carefully, you can find one Note under table 9, “Input supply for switching regulators must be capable to sink current to avoid overvoltage condition during the power down sequence of the device”. It means that the front power device (1st level power device) which provides input for PF82 bucks should have the sink current capability. Otherwise, some scenarios as the power down process may cause Vin overvoltage to damage PF82(EOS).

It is responsibility of customer to ensure this point. Generally, if the low-side of the front BUCK which provide power for PF82 uses MOS not Diode, it will have some sink current capability by experience.

To avoid the issue, customer can spread the Power down Sequence as wide as possible. It will reduce the sink Power back to VIN. Monitor the VIN of PF82 is also every important, if the overvoltage of the PF82 input happen, the best way is to disable the front power device output to avoid the risk.

The easy way for customer is to choose functional safety PMIC, as FS85 or FS56 in NXP, these products have real time output monitor and can disable the output when VPRE OV happen, so as to enter safe sate to avoid the PF82 damage.

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455 Views
adevries
Contributor V

Thank you!

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478 Views
guoweisun
NXP TechSupport
NXP TechSupport

I will reproduce this issue in the EVB please wait for response next!

 

465 Views
adevries
Contributor V

Hi @guoweisun,

 

Any luck reproducing this behavior with the PF8200 eval board? A couple months ago, I was using the EVB to examine this behavior, so it should be possible.

 

Thanks

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