MSP430F5510: spike noise when using ADC

Ben Qin

Part Number: MSP430F5510

Hi Team,

There's an issue from the customer need your help:

When the ADC is sampling, there will be a small spike noise for each sample. For example, with 50kH sampling, there will be a spike on the signal every time a sample is taken.

Self-made board, using F5510.

on left is original signal, on right is signal when AD sampling.

following is part of circuit:

3.3V is using DC-DC converted.

Could you help check this case?

Thanks & Regards,

Ben

over 2 years ago

0 Xiaodong LI over 2 years ago

TI__Mastermind 23295 points

Hi Ben

Please remove L2 of VD3.3 and check the waveform again.

Please check if MCU is in free run mode or debug mode during ADC conversion?

0 David Schultz over 2 years ago

Guru 25155 points

Sampling (charging the sampling capacitor) is always going to alter the input. Usually to decrease the voltage though.

This of course depends on the source impedance. Which is unknown here since you failed to include any information at all about that.

Then you get into details of the power supply. This shows you taking care to filter AVcc but not AVss. Best practice would include good decoupling as close as possible to the MSP430 power pins and star connections to the ground and output pins of the voltage regulator. The low output impedance of the regulator tending to short out any power noise.

0 Ben Qin over 2 years ago in reply to Xiaodong LI

TI__Intellectual 2690 points

Hi Xiaodong,

Removed L2 and still have spike.

MCU should be in free run mode.

Best Regards,

Ben

0 Xiaodong LI over 2 years ago in reply to Ben Qin

TI__Mastermind 23295 points

Hi Ben
May I know ADC10SHTx.ADC10CTL0 setting? is it the default value?
if yes, Please increas this setting for example 0100b = 64 ADC10CLK cycles and check if the spike noise can be reduced

Thanks

0 Ben Qin over 2 years ago in reply to Xiaodong LI

TI__Intellectual 2690 points

Hi Xiaodong,

I tried to add it here but I can’t remove it. The following is the register configuration of my ADC10

For the power supply, I have replaced the stabilized voltage source and other power supply chips for power supply, but the spike still cannot be removed.

Best Regards,

Ben

0 Xiaodong LI over 2 years ago in reply to Ben Qin

TI__Mastermind 23295 points

Hi Ben

You used mov.w. I think bis.w will be recommended to set the bit. But I think the asm code should be fine.

Could you please double check the value of ADC10SHTx.ADC10CTL0 during debug?

If the ADC10SHTx.ADC10CTL0 value is 64, could you please change this register to more higher values for the test (128 ADC10CLK cycles and 256 ADC10CLK cycles)

Thanks!

0 Ben Qin over 2 years ago in reply to Xiaodong LI

TI__Intellectual 2690 points

Hi Xiaodong,

The ADC10SHTx still has the previous glitch after turning it up, and the glitch size is basically the same (both the ADC128CLK cycle of 256 and 10 has been tried)

Best Regards,

Ben

0 Xiaodong LI over 2 years ago in reply to Ben Qin

TI__Mastermind 23295 points

Hi Ben

I will discuss with team on this noise and reply to you later

Thanks

0 Ben Qin over 2 years ago in reply to Xiaodong LI

TI__Intellectual 2690 points

Hi Xiaodong,

Is there any update?

Best Regards,

Ben

0 Xiaodong LI over 2 years ago in reply to Ben Qin

TI__Mastermind 23295 points

Hi Ben

This is normal there is a small spike noise for each sample. So, we increase sample time by ADC10SHTx.ADC10CTL0 setting. The spike noise for each sample still can be seen. The ADC conversion code should be correct because this spike noise has been avoided by sample time increased.

Thanks!

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MSP430F5510: spike noise when using ADC