MSP430FR5969: Large current on vref+

Hi Nick,

The VREF shouldn't be connecting to the AVCC and DVCC pins. The VREF should connect to VREF and AVSS if using an external reference see below image from the datasheet. Also the 10-12mA is high, are you able to reduce the current?

The risk could be damaging the internal circuitry so I highly recommend against inputting too much current, especially for long periods.

Regards,

Luke

Thanks for the response Luke Ledbetter

VREF+ isn't connected to AVCC and DVCC.

VREF+ is connected to an external +1.9V source.

As the AVCC and DVCC supply is powered OFF, VREF+ is larger than AVCC + 0.3V and DVCC + 0.3V. Which exceeds the max absolute rating.

It appears current is flowing through the MSP430 from VREF+ to AVCC & DVCC. 

I'm measuring 1.0V on AVCC and 1.0V on DVCC using a multimeter.

Wondering, what exactly internal to the MSP430 is being damaged? Is it isolated to VREF+? Can VREF+, AVCC, and DVCC tolerate this backpower? 

Yes, you are likely damaging the ESD diodes, not only that you are powering the cpu core with 1.6V which may put it in a weird state.

Hi Nick,

It is hard to say what exactly would be damaged in the circuit since we don't test for that. It is best to develop a system to avoid back powering, can you run the VREF through a transistor or does your reference have an enable pin? I created a small idea to help with a potential solution, but this would be dependent on your system. The main goal is to guarantee that the MSP will power on before receiving input from the VREF.

Regards,

Luke

Luke LedbetterUnderstood, can you share a diagram and / or description of the internal structure / architecture from VREF to AVCC & DVCC so I can speculate what internal components are being damaged?

Thanks for the response Keith Barkley 

https://www.ti.com/lit/an/slya014a/slya014a.pdf?ts=1678210473344&ref_url=https%253A%252F%252Fwww.google.com%252F

Hi Nick,

David posted a nice article on the ESD diode structures but I want to preface these are for ESD protection and doesn't support the high current you're seeing.

In the User's Guide you can see a diagram of the ADC block diagram and some connections on the VREF. Again I highly recommend against having the reference input before the device is on, as you violate at least 2 absolute maximum operating conditions.

Regards,

Luke

Those diodes can most likely carry that much current. But not without hazards. They are small so could be damaged. A more important hazard is that excess current could result in latchup.

The diodes will be present no matter which function you chose for the pin. GPIO or Vref.

This particular problem could be mitigated by powering the external Vref source from the same Vcc that powers the MSP430. So when Vcc drops out, so does Vref. A series resistor would limit the fault current but probably wouldn't do much for the accuracy of the external reference voltage.