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Does CURRENT_STRENGTH_NEW limit current?

BrendenB
Novice
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Is the output current from a pin limited when CURRENT_STRENGTH_NEW is set? For example, if I set CURRENT_STRENGTH_NEW to 10mA will the pin only allow 10mA out? If not, is there any pin setting that might be used to limit the current sourced/sunk at a pin?

 

I always thought that setting CURRENT_STRENGTH_NEW was just telling the FPGA to configure the pin so that the voltages required by the IO_STANDARD can be generated while the current sourced/sunk is less or equal to CURRENT_STRENGTH_NEW. It would still be possible to source/sink more than CURRENT_STRENGTH_NEW of current, but at that time the voltages may start violating the IO_STANDARD levels (or cause smoke).

 

The reason I ask is that the "HSMC Debug Header" from terrasic has LEDs connected directly between *two* FPGA pins without a resistor in series (there is actually a 0Ω resister but I assume it does nothing). I assumed that when the LED was turned on (by setting one pin to 1'b0 and one to 1'b1) that massive current would be generated and smoke would follow. I'm not sure what happens but I am assuming it works. Just trying to work out why. The DE10-Standard board that I am using routes FPGA pins directly to the HMSC connector (i.e. no resistors).

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FvM
Honored Contributor II
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Hi,
current strength specification has nothing to do with limiting output current to a certain value. The mA value defines the maximum load current that keeps output voltage drop within the logic level specification of a certain IO standard. Maximal output current, e.g. into shorted output is much higher and exceeds in most cases FPGA maximum rating so that the output driver may be damaged.

 

See for example the output characteristic of Cyclone 10 LP CMOS 3V IO standard with 4 mA current strength according to IBIS files.

FvM_0-1728904570257.png

The only IO standard that limits output current to a safe value is LVDS 2.5 V. HSMC breakout adapter is obviously designed to use this standard.

FvM_0-1728905353639.png

 

 

 

 

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6 Replies
AqidAyman_Intel
Employee
805 Views

We sincerely apologize for the inconvenience caused by the delay in addressing your Forum queries. Due to an unexpected back-end issue in our system, your Forum cases, along with others, did not get through as intended. As a result, we have a backlog of cases that we are currently working through one by one.

Please be assured that we are doing everything we can to resolve this issue as quickly as possible. However, this process will take some time, and we kindly ask for your patience and understanding during this period. The cases will be attended by AE shortly.

We appreciate your patience and understanding, and we are committed to providing you with the best support possible.

Thank you for your understanding.


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AqidAyman_Intel
Employee
794 Views

Hi,


CURRENT_STRENGTH_NEW is a current strength logic option where it is a logic option that sets the drive strength of a pin. Specific numerical strength settings are appropriate only for pins with certain I/O standards. Specify a number (in mA), MIN, or MAX for output or bidirectional pins that support programmable drive strength. This option must be assigned to an output or bidirectional pin or it is ignored.


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FvM
Honored Contributor II
779 Views

Hi,
current strength specification has nothing to do with limiting output current to a certain value. The mA value defines the maximum load current that keeps output voltage drop within the logic level specification of a certain IO standard. Maximal output current, e.g. into shorted output is much higher and exceeds in most cases FPGA maximum rating so that the output driver may be damaged.

 

See for example the output characteristic of Cyclone 10 LP CMOS 3V IO standard with 4 mA current strength according to IBIS files.

FvM_0-1728904570257.png

The only IO standard that limits output current to a safe value is LVDS 2.5 V. HSMC breakout adapter is obviously designed to use this standard.

FvM_0-1728905353639.png

 

 

 

 

AqidAyman_Intel
Employee
725 Views

He Brenden,


I wish to follow up with you, do you have any more concerns or questions on this issue?


Regards,

Aqid


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BrendenB
Novice
710 Views

Nope. Marked the solution.

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AqidAyman_Intel
Employee
682 Views

I’m glad that your question has been addressed, I now transition this thread to community support. If you have a new question, Please login to ‘https://supporttickets.intel.com/s/?language=en_US’, view details of the desire request, and post a feed/response within the next 15 days to allow me to continue to support you. After 15 days, this thread will be transitioned to community support. The community users will be able to help you on your follow-up questions.


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