# TMCS1126: demo board output 20mV noise when there is no input

Part Number: TMCS1126

Tool/software:

Hi experts,

Customer is using TMCS1126A1 on their own board. A1 is 20mV/A. They found that output has a 20mV noise when there is no input, both on their own board and TI demo board.

Do you have some suggestion to remove the noise?

• Gary,

If the customer does not need the full bandwidth then you will need to filter.

https://www.ti.com/video/4078827152001

Assume 1/f noise =not an impact

A1 = 25mV/A

Noise density: 150µA/√Hz

Bandwidth: 550kHz

Assume single pole at output: 1.57

RMS noise = 1.57*150µA*√550000Hz = 175mA

RMS noise in output voltage = 175mA/25mA/V = ~7mV

Peak to Peak = RMS *6  = 42mV

Regards,

Javier

• Javier,

That is more of an excuse than an answer.
I too, see this noise in my application in all the TMCS sensors.
The problem is that the noise is random and "LOW" frequency.
To filter it would make the sensor useless for control and it's response time irrelevant.
Pretty sketchy marketing here.

Steve

• Hello Steve,

What is the issue you are seeing exactly for low frequency.  From the question above I had no context of low frequency noise.  Is your issue with the TMCS110x family.  As we have an explanation of that in this application note:  An image below from that application note.

Can you share what device you are using and a screen shot of the low frequency noise?  Also if you have a definition of low frequency.

Regards,

Javier

• Gary,

Here is a correction on expected noise.  I placed the 1.57 outside the Sqrt.  I highlighted the updated values.

Assume 1/f noise =not an impact

A1 = 25mV/A

Noise density: 150µA/√Hz

Bandwidth: 550kHz

Assume single pole at output: 1.57

RMS noise = 150µA*√(1.57*550000Hz) = 139mA

RMS noise in output voltage = 139mA/25mA/V = ~3.5mV

Peak to Peak = RMS *6  = 21mV

Regards,

Javier