REF102

Dany,

First, you need to know that trimming the output voltage of REF102 will change the voltage drift by at least 0.008ppm/C per mV of trimmed voltage (see page 6 of the datasheet). Below please see a simplified REF102 circuit topology showing ~400mV Vout adjustment using 20k potentiometer.

In order to improve the trim resolutio, the circuit below includes Rs=150k external resistor with a trim range of around +/-100mV.

Attached please find REF102 simplified Tina-TI schematic which you may use for your own simulations.

You may download a free Tina-TI by clicking on the link below: 

REF102 Vout Adjustment.TSC

I tried to open the above design with Tian-TI V9 but I always get the following message:

Unable to open C:\...

REF102 Vout Adjustment_V7.TSC

Attached should open in TINA-TI V9.

Thanks it works!

Now I have another question. I replaced the trim pot by 2 resistors (13K and 7.5K) and removed the 150K to get 9.9V at the ouput. When I tried these resistors on my circuit I got 10.058V at the ouput.

Do you know why the output voltage values are so different.

One more thing, if I place a trim pot on my board, the resistors value to get 9.9V are 3.73K and 15.94k. Tha same resistors value in TINA-ti give 9.77V at the output.

Is it a good design practice to use only one resistor between Vtrim and Vout to set the output voltage. With a value of 169K between Vtrim and Vout I'm able to get the output voltage arround 9.90V.

You will need individually trim each REF102 with a different resistor value as no two parts will be exactly the same.