[ARM] Help on MCP4018 digital POT

i m using MCp4018 digitalpot i m getting 8.57 v while sending write( 0x00);
0x01 =7.28 v
0x02 =6.37v

0x03 =5.68

0x05=4.76 I need to calibrate it get 6V,5V how to get exact voltage

Hi,

a digital pot doesn´t output a fixed voltage, it always depends on input voltage and connections.

Without knowing your circuit it is impossible to answer.

Klaus

here i attached circuit diagram

i am getting
write_data (0x00)= in output m getting 8.3v constantly
write_data (0x01)= in output m getting 7.2 vconstantly
write_data (0x02)= in output m getting 6.3v constantly
I need 6v constant how to calibrate
write_data (0x03)= in output m getting 5.6v constantly
I need 5v constant how to calibrate

write_data (0x04)= in output m getting 5.16v constantly
write_data (0x05)=in output m getting 4.76v constantly

Hi,

In your first post you didn´t mention the voltage regualtor.... And the voltages you talk about are the voltage regulator outputs. At least this is what I assume.

You never mentioned that it is a 5kOhms pot. We have to find it from the datasheet.

--> you really make it difficult for us to help.

From the values you give I doubt your input voltage is near 12V.
added: Or you somewhere have a series resistor fo about 100 Ohms

*****
You urgently need to read the MCP738100 datasheet!!!
You want adjuatable output voltage, then please read the section "7.3.1 Adjustable Operation"
-> It says: "The value of R1 should be less than 4.17 kΩ...".
If you are not that experienced, I recommend to strictely follow such guidelines.

In your diagram I see you want adjustable output voltage range from 4.5V to 7V.

Now I´m doing the accurate calculation for this.

The formula in the datasheet says V_out = 1.21V(1+R2/R1) + I_FB * R2
V_FB = 1.21V, I_FB = 3uA

Let´s say we keep your R2 = 1k

Calculation for R1 to get 4.5V
(the term I_FB x R2 is constant and can be replaced by 3uA x 1k = 3mV)
now the formula is: 4.5V = 1.21V * (1 + 1kOhm/R1) + 3mV
--> 4.497V = 1.21V * (1 + 1kOhm / R1)
--> 3.7165 = 1 + 1kOhm/R1
--> 2.7165 = 1kOhm / R1
--> R1 = 1kOhm / 2.7165
--> R1 = 368.1 Ohms

****
do the same for 7.0V

Klaus