FAQ: AD8309 Limiter output swing

Document created by Jim Employee on Jan 20, 2010Last modified by AndyR on Jan 31, 2012
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Q.

As per the AD8309 data sheet the limited output VLIM = VS – 400 mV × RLOAD/RLIM (data sheet page no:17). In our design we have RLOAD=499 ohms & RLIM = 402 ohms. For this we are getting 250 mV output in each pin. It didn't match with the given relation?

 

 

 

 

 

 

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A.

You are bandwidth limited due to the choices of resistors you are using and the capacitance of the test equipment. With the resistor choices and the capacitance of the measurement equipment there is a low pass corner frequency of 20 MHz. This is what is causing the voltage to drop off. If you were make the resistors 5 times smaller you achieve the same voltage swing and increase the bandwidth. This will also cause an increase in the current. The current would increase from 1 mA to 5 mA.

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