LM7121: Maximum Output Short Circuit Current

Hi Kevin,

as the maximum value isn't specified in the datasheet you can only make an estimation. 54mA is about 25% below 71mA. So 25% above 71mA would be about 90mA. Again, this is only an estimation.

Can you show a schematic of your circuit?

Kai

Hi Kai,

Thanks for your reply. I did this same thing you did with regard to estimating the maximum output current. Has this been tested, and if so is there data that you can share with me?

I'm sorry, but I cannot share my circuit with you.

Thanks, 

Kevin

Actually I just sent in an article on this topic of output current - normally, you are interested in minimum linear output current you can depend on. Very few high speed amplifiers have an actual short circuit protection circuit so the numbers in the LM7121 are just where the base drive for the output stage runs out of steam for an actual short to ground condition. 

And yes, if you are interested in fault conditions to a shorted ground, this is the right question, 

If you are interested in output current available that will still yield linear operation, these curves are much more useful, And then what I said in the article is these are typical process case curves and over production you should probably guardband the knee down at least 20%. 

Hi Michael,

Thank you for the reply to this topic.

I am indeed interested in the amplifier's response under an output short to ground fault condition. In-between the LM7121 amplifier output and the load is a device that has a maximum current threshold, which when crossed will be damaged. The circuit must survive a condition in which the load is a short circuit to ground. This is the reason for my question regarding the maximum value of output current the amplifier can source/sink under this condition.

Well, without firing up full designer PDK sims that will be hard to come by (not likely on a part his old). Sometimes what folks do is put a small resistor in the supplies that collapses the supply voltage if a short circuit condition exists - then you get into input overdrive questions while this is going on but if the normal load current is not very much and say your min short circuit current is 30mA on +/-5V supplies, a 166ohm R will collapse it - you would of course put your decoupling cap on the other side of this at the device supply pins and this will of course degrade the PSRR. 

Hi Michael,

that's exactly what I wanted to suggest and what I wanted to see the schematic for :-)

Kai

Hello Kevin,

   Kai's estimation on linear max output current sounds correct due to our devices being specified on a distribution for some of the listed specs. As Michael stated, this is an older device, and do not have the fault condition for this part. We could recommend a different device if you are able to share the main specifications you are looking for and the device's max current threshold.

Thank you,

Sima