XTR115: XTR115 about the limit current question

Mickey Zhang

Genius 12080 points

Part Number: XTR115

Hi team,

The customer would like to use XTR115. The limit current for XTR115 is 32mA in the datasheet. But the customer would like to limit the current to 25mA.

Is there any solution?

Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments

over 8 years ago

0 Mickey Zhang over 8 years ago

TI__Genius 12080 points

Hi team,

Is there anyone to see my question? The customer is waiting for my reply.

0 Zak Kaye over 8 years ago in reply to Mickey Zhang

TI__Mastermind 23050 points

Hi Mickey,

You can limit the current further by placing an additional resistor between the emitter of the transistor and the emitter pin of the XTR115. I believe a 36 Ohm resistor should produce the desired limit of 25mA, but I would suggest testing to verify. I will try to get some samples of the device and mock up a test board in parallel with your customer testing.

Regards,

Zak Kaye

0 Mickey Zhang over 8 years ago in reply to Zak Kaye

TI__Genius 12080 points

Hi Zak,
Would you explain more about this? How to calculate to get the 36ohm? Can you provide a circuit?

I see a similar post :

0 Zak Kaye over 8 years ago in reply to Mickey Zhang

TI__Mastermind 23050 points

Hi Mickey,

I calculated the 36Ohm resistance by making a few assumptions and working backwards to estimate what the Rlim resistance would have to be in order to limit the current to 32mA, and how much it should increase to limit the current to 25mA. After looking deeper into the issue however I do not believe this is a very robust solution because Rlim is a dynamic resistance implemented with active circuitry and thus it would be very difficult to hone in on a 25mA limit with an external resistor. You may be able to tune in an appropriate value for this resistor based on your supply voltage and Vbe of the selected transistor, but if you want a more reliable and robust solution for your customer I would suggest implementing an external active current limiting circuit per Collin's recommendation.