MSP430FR5969-SP: UART Issue with M4FR5969SPHPT-MLS

Mayank Mishra

The UART transmitter cannot be selectively depowered and is normally high. It’s voltage is leaking through the deenergized MSP430 and is pulling up the 3.3V power rail up to about 1.9V. The MSP430 datasheet only specifies I/O voltage maximums as they relate to VCC. No failsafe capability is indicated. Can you review this with T/I and find out whether the part can tolerate this configuration indefinitely without electrical overstress or other damage to the MSP430?

Part Number is : M4FR5969SPHPT-MLS

over 3 years ago

0 David Schultz over 3 years ago

Guru 26235 points

This is power being injected into the MSP430 Vcc via the input clamping diodes. Not usually a big problem unless it provides enough power to keep the MSP430 running when you want it off. There is an absolute maximum diode current listed in the data sheet.

0 Keith Barkley over 3 years ago

Guru 43795 points

"The MSP430 datasheet only specifies I/O voltage maximums as they relate to VCC."

Right, and in this case your Vcc is zero.

0 JD Crutchfield over 3 years ago

TI__Mastermind 30545 points

Back powering of the MSP430 through it's ESD diodes is described in the first section of this MSP430 ESD Diode Current Spec app note. Ultimately, this condition of VCC on the GPIO pin of an unpowered MSP430 should be avoided.

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MSP430FR5969-SP: UART Issue with M4FR5969SPHPT-MLS