Hi NXP expert,
When I do shipping mode validation, I found an abnormal current leakage in NX20P0407 when VSYS=0V in shipping mode;
Abnormal finding: NX20P0407 has an equivalent 75K pull down resistance on SBU1 line(system side) when VSYS=0V, which is not defined in datasheet's block diagram.
Schematic:
The system side SBU1 is only connected to MCU's SWDIO(MCU: nRF52840), which has 13K pullup resistor(V_pullup=3.3V);
In my application's shipping mode, MCU is alive but NX20P0407 will be disconnected from power(VSYS=0V); When i did measurement on the SBU1 pin, found SBU1 pin's voltage is 2.8147V, which means there is 75K pull down resistor on SBU1 line and also caused 37uA current leakage;
I also tried to de-soldering the NX20P0407, and the 37uA current leakage disappear which double confirmed that NX20P0407 caused the current leakage;
So i would like to confirm whether my finding is correct or not, and if that's correct, why it is not specified in the data sheet, many thanks!
Hi Zong,
I suspect the leakage current is flowing from the SBU1 pin to VSYS, than to the GND through the pull-down resistor. Please try to disconnect the VSYS pin completely and see if the leakage current will decrease. The 32uA leakage current is closest to the leakage current you see. Please make sure you have pulled the SBUEN pin to GND when the NX20P0407 is unused. Leaving the SBUEN floating may pull it high by an EMI.
With Best Regards,
Jozef
Adding the simplified block diagram related to NX20P0407 for reference.
Thanks for you quick response, please see my reply as below:
Have you connected the VSYS to GND? Or have you left it floating?
--Reply: There is a load switch between PP3V3 power rail and NX20P0407's VSYS; MCU will turn off the load switch to de-power NX20P0407 in shipping mode;
How is the rest of the NX20P0407 pins connected in shipping mode
--CC1&CC2 are connected to PD controller's CC lines which is also being de-powered in shipping mode, SBUEN is connected to the same PD controller's one GPIO; SBU2 is connected to MCU's SWDCLK which has internal pull down resistor;
Hi Zong,
thank you for detailed description and schematic. Please confirm how you have connected the VSYS pin in shipping mode (when you measured 37uA on SBU1 pin). Have you connected the VSYS to GND? Or have you left it floating? How is the rest of the NX20P0407 pins connected in shipping mode?
With Best Regards,
Jozef
Hi Jozef,
Please see my reply as below:
Please try to disconnect the VSYS pin completely and see if the leakage current will decrease.
--1' I tried to cut the VSYS trace to disconnect VSYS completely, the leakage current didn't decrease;
--2' Furthermore, I also tried to apply wire to re-connect the 2 ends of the cut VSYS trace and series a DMM between to check whether there is leakage current from VSYS in shipping mode, the measured current is nA level, almost 0.
--3' Also measured the VSYS voltage in shipping mode, the result is 1~3mV;
Please make sure you have pulled the SBUEN pin to GND when the NX20P0407 is unused. Leaving the SBUEN floating may pull it high by an EMI.
--Since SBUEN pin has a pulldown resistor in NX20P0407, i only measured the SBUEN's voltage in shipping mode, the result is also 0V; And I also de-soldering PD controller where NX20P0407's CC&SBUEN are connected to, the leakage current was still same as before.
So i'm still inclined to that the current leakage happens inside NX20P0407, please share your comment, many thanks!
Hi Zong,
thank you for the tests. Ok. This confirms the leakage path. The "shipping mode" is not defined in the NX20P0407 datasheet so no values are defined for this mode. Neither is guaranteed no leakage current when NX20P0407 is not powered (e.g. pins in high impedance, when VSYS=0V). If there is a way to get rid of the SBU1 and/or other pins leakage current, I would need to contact an application engineer. They always require following information. Please share.
Customer: ? (company)
End Customer: ?(also company, same or different)
End Application: ?
Country: China
Annual Volume: ?
With Best Regards,
Jozef
Please see the info in private message.