0
\$\begingroup\$

Using MSP0G1505 MCU. It has a inbuilt DAC. I thought it could give me 0 to vdd as output but it seems it can only give 0.3 to vdd-0.3 as output. This happens because of the offset and gain errors. From 0.3 to 3 (vdd=3.3) dac's output is linear.

DAC's signal goes to an op-amp in a constant current sink configuration. So I had planned that with a 100 ohm resistor 0-3.3v will map to 0-33mA of current but min value of DAC is 0.3v. So now I am planning to put 1 more opamp whose function will be to map (0.3v-3v)signal to (0v-2.7v) . Is there any other way to solve this or I will have to make this hardware change?Just looking if there might be any other way in which I can avoid this hardware change. Thank you.

edit:

op(pin3) is where the dac is connected. lets say only NMOS15 is only turned on. enter image description here

\$\endgroup\$
3
  • \$\begingroup\$ Show the current OpAmp circuit. It may be possible to add an offset somewhere. \$\endgroup\$
    – Jens
    Commented May 24 at 1:05
  • \$\begingroup\$ @Jens Have added the picture. \$\endgroup\$
    – funtastic rdj
    Commented May 24 at 4:42
  • \$\begingroup\$ If you change R43 to, say, 10 kohm and add another resistor from IN1- to a supply, you can offset the voltage at IN1- to 0.3 V at no current to match the DAC offset. I will place an answer if there is time. \$\endgroup\$
    – Jens
    Commented May 30 at 1:06

0

Reset to default