Hi experts,
My customer is using the MSP430FR5964IZVW's 12-bit internal AD function port as Input for monitoring settings, but a pulse-like voltage is generated from this port, and the microcontroller itself reads it, causing a problem with reading different voltages.
Could you give me your opinion on possible factors and countermeasures for the following symptoms?
[Problem]
A waveform like the one shown on the below was observed at the ADC port of the MSP430FR5964.
The original waveform observed by the ADC is a flat waveform, and when connected to the microcontroller ADC port, it becomes a waveform that emits a ripple like the one on the below.
Signals like the one on the below are output only from pins A7 and F4 (ADC channels A15 and A9) and are not seen on other ports for ADC.
Also, the microcontroller port was measured directly with an oscilloscope, and the pulses were also generated when only the pull-down resistor to GND was measured, which leads us to believe that the pulses are generated by the microcontroller.
Since these pulses are generated in the same cycle as the timing of voltage acquisition by the ADC of the microcontroller, it is possible that the pulses are generated at the timing of ADC acquisition of the microcontroller.
In addition, this kind of waveform is generated only when the microcontroller is started up from sleep. (approximately 3sec)
The power supply system of the circuit is battery => step-up DC/DC converter (3.3V) => LDO (3.0V) => microcontroller, and this problem occurs only when the microcontroller voltage (3.0V) < battery voltage.
Some experimental results are attached below.
Please allow me to share the actual schematics and I/O map settings in a private chat due to customer migration.
If you have any missing information or points that need to be confirmed, we would appreciate it if you could point them out.
Best regards,
O.H
