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Adjust Vout of ADM7155 during operation

Question asked by bene on Mar 7, 2017
Latest reply on Mar 9, 2017 by Jason_Duan

Hi, we use the ADM7155-04 in our desing as a low noise linear regulator. We have an input Voltage of 5V and need to generate between 1.8 and 3.2 V. I did built up the circuit exactely as it is mentioned in the datasheet. To adjust the voltage I wanted to use a simple potentiometer in the resistive divider. As I had the components available here, I chose 0k-5k  in series with 2.1k for R1 and 4.2k for R2, which should give me 1.8V - 3.2V. I shorted enable and Vin of the ADM.

 

Here is my problem: When I turn the system on, the output voltage fits to the setting of the resistive divider. But when I adjust the potentiometer, the output behaves odd. When I want to increase the output in a linear way, increases in discrete steps of approx 300-400mV. When I want to decrease the voltage again, it linearly decreases but only to 2V and not down to 1.8V (for Rpot = 0k; however, when I turn the system on with Rpot = 0k, I get the 1.8V)

 

Any idea, what I did wrong? Do you need more information?

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