PCB with current Limiter Circuit

[Abinayaparamasivam]

Hello,

I am designing one PCB with comparator (LMH6629). In this I need to add one current limiting part(which should reduce 18 mA to 12 mA). Can I add FET at my output side? or which is suitable for this? but there should not be a voltage drop.

 

[erikl]

There's no FET current limiter without (any) voltage drop. To achieve this, you need to limit the current with an active negative feedback control circuit.

 

[Abinayaparamasivam]

Thanks for your response.

My output signal should be( 2V to 0.6V) Square pulse and the current should br less than 12 mA How can I achieve this?

 

[KlausST]

Hi,

your information is not complete, therefore it is imossible to answer.

As said: there is no current limiter without voltage limitiation.
You can´t have a 2V signal without voltage drop, but current limited to 12mA.

Maybe it´s better to tell us what´s the use of your circuit.
Supply voltages, output voltage_range_low, output voltage_range_high, frequency, load (range) and so on.

Klaus

 

[Abinayaparamasivam]

Hi,

I need to design the PCB (comparator ckt).The output of this board is connected to the Daughter card of FPGA board.
The I/O standard of the daughter card pin is LVCMOS25. Single ended 50 ohm termination

As per the daughter card details, the current should not exceed 12mA, based on this I need to design the board.

Input : 0V to 2V
Output: (2V-0.6V)
output voltage_range_low: 0.6V
output voltage_range_high: 2V
Comparator: LMH6629
Supply voltage of comparator: 2.9V
Termination:50 ohm

 

[KlausST]

Hi,

There´s something wrong with your specification:

*****
You said: "comparator (LMH6629)"
But this is no comparator, it is an amplifier.
--> If you want a comparator, then use a comparator. If you want an amplifier, then use an amplifier.
Using an amplifier as a comparator has it´s drawbacks, because it is not designed for this.
There are already threads about this topic.
*****

Please use Ohm´s law:

you said:
* 12mA limit
* 50 Ohms termination
* Output_voltage_high: 2V

This is not possible:
12mA into an 50Ohms load will give just 600mV, impossible to get about 2V.

--> review your specifications

***
Supply voltage: 2.9V
--> single: 0V/2.9V or dual +/-2.9V?

Give correct and complete specifications. Best is to give the datasheets. And a schematic.

Don´t make the thread more lengthy than necessary.

Klaus