TMCS1108: TMCS1108

brittany cohen

Part Number: TMCS1108

Hi there, I am using a bidirectional motor and bought the TMCS1108A3B to measure our current off of the motor. I am not sure if I am using the equations from the datasheet right as I do not get the IN LINEAR MEASUREMENT RANGE from table 5-1 and I have been confused about how to include the swing to supply and ground into the input current equation. How do I calculate these values? equations 20 and 21 show how to find In max + and In max - but I don't understand how to calculate properly for In. I am attaching two images of equations I wrote out to try and figure out In from the current sense chip. Can someone tell me what I am doing wrong?

https://drive.google.com/file/d/1C3KhoOqdKtS8W7_VbiKb9LlsFcTOKSo_/view?usp=sharing

https://drive.google.com/file/d/1NjpaiqysOnEmyTXm9s08IutF34x3Rpkb/view?usp=sharing

over 3 years ago

0 Javier Contreras4 over 3 years ago

TI__Mastermind 32290 points

Hello Brittany,

The table is a little off and the output is not symmetric for high and low. Below example for the bipolar. Also I would design a further away from the swing values. If my example below is not clear enough let me know. I used equations 18 through 21.

For Vs = 3.3; S = 200mV/A; Swing High 0.1V from rail; Swing low is 0.01V from GND.

Vout Max =3.3-0.1V = 3.2V

Vout Min = 0.01V

Vout 0 = 1.65V

InMax = (3.2V -1.65V)/(200mV/A) = 7.75A

InMin = (1.65V -0.01V)/(200mV/A) = -8.2A

0 brittany cohen over 3 years ago in reply to Javier Contreras4

Prodigy 30 points

That makes sense but I still don't understand what the equation should be to find I In to account for the swings bc equation 1 does not account for the swing.

+1 Javier Contreras4 over 3 years ago in reply to brittany cohen

TI__Mastermind 32290 points

Hello Brittany,

Swing only limits current that can be measured. If your current is above those values swing still not allow as you will clip the output. So equation 1 will hold till you hit the limits of InMax and InMin.

Another way to look at it is that equation 1 will hold from Vout = 0.01V to VS - 0.1V. Please keep in mind you should design to within this values.

+1 brittany cohen over 3 years ago in reply to Javier Contreras4

Prodigy 30 points

ah this is super helpful! thank you!

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TMCS1108: TMCS1108