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ASL2417 Limp home mode not working after short power interrupt

Hello,

We are using an #ASL2417 in an aircraft environment to drive LEDs of the cabin lights. The IC was chosen because of its limp home capability that allows light functionality under circumstances where the CPU of the device is not available.

Unfortunately, we have now discovered that the lights turn completely off after a power interrupt that is less than 20 ms and don't come back on again until a power cycle. This is happening both during normal mode and in limp home mode with the CPU not powered.

With longer power interrupts, the ASL2417 acts as expected: The lights flicker, but remain on after the interrupt. Only when the interrupt is less than 20 ms, the lights stay off.

Has anyone encountered this problem already and found a solution? The working theory at the moment is that VGG drops too far and the chip goes into the fail silent-mode from where it cannot wake up again. Even though the interrupted power supply should cause the chip to go into undervolt-mode from where it can return to operating mode (in Limp Home) after the interrupt has passed and power is applied again.

Could it be that Undervoltage requires more time to trigger than VGG_Error?

Best regards,

Thorsten

Re: ASL2417 Limp home mode not working after short power interrupt

Hi @T_Schroeder,

Thank you for sharing your solution with the community!

Re: ASL2417 Limp home mode not working after short power interrupt

Thanks for the help.

I have managed to trace the problem to the fact that the step down stages and VIN were separated by a diode that caused VIN to drop considerably slower in voltage than the actual supply-voltage for the step down-stages.

After I removed the diode, VIN now exactly tracks the voltage and the MOSFETs and the chip handles power interrupts from 2ms to 500 ms without problems.

Re: ASL2417 Limp home mode not working after short power interrupt

Hi @T_Schroeder,

Thank you for contacting NXP Support!

According to the ASL2417 datasheet, the Fail Silent mode can be produced by exceeded junction temperature or a VGG error.
Based on your description, the ASL2417 is entering to the fail silent mode by a VGG error, this error is set when the VGG can't be regulated and therefore, the output current is disabled.
In this case, could you please share your schematic to verify these connections?
Also, could you please share your selected value for Limp_timeout?

Please share this information to continue with the support.

Have a great day!