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Is there a current DAC which has 0 current (< 1 nA) for an input code of 0? I am driving an LED, so would it make sense to use bipolar supply rails (where a negative output would reverse bias the LED and give 0 current)? For my project the current error must be less than 1 uA and the FSR need only be greater than 200 uA. My current design uses an 8750 from ti, which has too high of offset current (0.01% of FSR = 2 uA).

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  • \$\begingroup\$ Why not just shunt the LED with a switch if you want to turn it off completely? \$\endgroup\$ – Spehro Pefhany Sep 14 at 19:03
  • \$\begingroup\$ My conscience tells me to vote to close this as a shopping question, but not quite. Have you looked at manufacturer's selection matrices and data sheets? \$\endgroup\$ – TimWescott Sep 14 at 19:29
  • \$\begingroup\$ You can always AC couple the output; then the zero bias will be totally under your control. \$\endgroup\$ – TimWescott Sep 14 at 19:35
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    \$\begingroup\$ Even if you had a 16-bit-accurate DAC, if the full scale current was something like 10mA your 1nA would be less than 0.01 LSB so essentially you have two regions of operation whether you want to think of it that way or not. \$\endgroup\$ – Spehro Pefhany Sep 14 at 20:08
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    \$\begingroup\$ If your led happens to get some light, it works as solar cell. The only way to keep the current = zero is to have a switch as already said. BTW To get useful answers you should tell what you try to achieve by keeping the current surely < 1 nA and what disaster a bigger current, say 2 nA would cause. \$\endgroup\$ – user287001 Sep 14 at 20:21
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I used a 100 uA current source in parallel with the LED (REF200 from ti), and now am getting pA of zero-scale current (the threshold voltage of the LED is greater than the output/saturation voltage of the current source (REF200)).

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