Current Sensing Circuit for ASIC Evaluation Board

hoyyoth

Joined Mar 21, 2020
196
Dear Team,

I need to design a current sensing circuit for one of my ASIC evaluation board.
The ASIC will take the current from 0.5mA to 1mA from a 1.8V Supply. Whatever the current it is taking voltage at Vout should remain constant at 1.8V.
Please see the attached circuit . The 1.8V supply is provided to ASIC via buffer, the current sense resistor is placed in the output of the buffer.
The issue I am facing is when ASIC is taking current the 1.8v gets dropped. May I know how to fix this issue.

Regards
Hari

AlbertHall

Joined Jun 4, 2014
12,072
Is this for a real world circuit or a simulation?
For a simulation use a much lower value sense resistor e.g. 1Ω

hoyyoth

Joined Mar 21, 2020
196
Hi Albert,

Thank you very much.
This is for the real-world circuits.
The Vout should be the 1.8V even after sense resistor drop.I mean sense resistor dro should be compensated before it reaches DUT(ASIC)
I am struggling to get a circuit like that. May I know your thoughts.

Regards
Hari

jpanhalt

Joined Jan 18, 2008
11,088
What do you have the series resistance of V3 set at?

AlbertHall

Joined Jun 4, 2014
12,072
For instance, in the LM317 datasheet, there is a circuit for a battery charger. This supplies a constant voltage, but limits the maximum current. If you set it up so the current limit is a good bit higher than your circuit draws then you will get a fixed output voltage and you can measure the voltage across the series resistor to know how much current is being drawn.

hoyyoth

Joined Mar 21, 2020
196

hoyyoth

Joined Mar 21, 2020
196
For instance, in the LM317 datasheet, there is a circuit for a battery charger. This supplies a constant voltage, but limits the maximum current. If you set it up so the current limit is a good bit higher than your circuit draws then you will get a fixed output voltage and you can measure the voltage across the series resistor to know how much current is being drawn.
Hi Albert,

Thank you very much.
I found one more circuit. But I am not able to understand why they put certain components. They are marked in a Redbox.
Please check it and let me know your thoughts.I would like to know whether the circuit do the purpose or not.

Regards
Hari

jpanhalt

Joined Jan 18, 2008
11,088
Did you leave it blank or set to "0?"

Simulation at R1 = 1.8V R1 can be any non-zero value -- 1.0 uΩ also gave V= 1.8.

hoyyoth

Joined Mar 21, 2020
196
Did you leave it blank or set to "0?"

View attachment 210889

Simulation at R1 = 1.8V R1 can be any non-zero value -- 1.0 uΩ also gave V= 1.8.
Hi Jpan,

I leave it blank.

Regards
Hari