Loop Calibrator design help

[hemnath]

Please check the following the pdf file.

 

[hemnath]

Can you help me in selecting the mosfet for the best performance? should I go for very low Rds?

 

[KlausST]

Hi,

read post #31.

R_ds_on.

The limit is: R = V / I = max_allowed_Voltage_drop_across_drain_source / Max_expectable_loop_current

If you allow (Please decide on your own) 2V voltage drop, then it is : 2V/0.02A = 200 Ohms. This is not very low.


Klaus

 

[FvM]

Almost any available MOSFET will have sufficient low Rdson for this application. You'll know if you start analysis and calculation of the circuit yourself.

Power rating might require to use not the smallest available package, gate leakage current is however critical.

 

[hemnath]

Thank you for your time guys. Can you help me in selecting the boost converter IC?

Battery voltage varies from 6 to 11V max. Output voltage: 24V. Output current: 100 mA.

 

[KlausST]

Hi,

https://www.linear.com/products/Step-Up_(Boost)_Regulators

Klaus

 

[hemnath]

Thank you. Lots of options.. I planned to select LT1317. I have no experience with boost converter. Did i selected the right one?

 

[KlausST]

Hi,

I'm not wiser than the selection tool.
Therefore I assume: yes.

I just wanted to add that every switch mode controller IC manufacturer has such selection tools. LinearTech is not the only one.
Even distributors usually have them.

Klaus

 

[hemnath]

Thanks. Can you specify any DAC with HART compatible? I have checked AD421, DAC161S997. But this doesn't goes upto 0 mA