MP20051 Issue with output voltage

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1

I am using a MP20051 to generate a reference voltage for my PECL design. All the 50 ohm resistors that is connected to each output is tied to this reference voltage (looking for this voltage to be around 1.3 V). I am using a 10k potentiometer to adjust my output (VBB). When I power it up, as I adjust the potentiometer, the voltage VBB starts at 3.3 volts on one end of the pot and quickly hits a limit of 2.4 volts going to the other end of the pot. Am I using this incorrectly?

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2

Hi @pursley ,

Can you send the part number of the potentiometer you are using, your VCC voltage, and the total load connected to VBB (i.e., the load current)?

Thanks,
Rubas

3

VCC = 3.3 V

I have tried 100k, 10k and 1k pots with little change in the output voltage.

I am unsure of the load current.  I have 26 50ohm resistors going from PECL outputs to VBB (which should be around 1.3 V).  Total current should be less than 600mA when the pot is set appropriately.

I did consider that my pot was too big.  Do I need something even smaller?
4

These are the part numbers of the pots that I tried.

3361P-1-104GLF
3361P-1-103GLF
3361P-1-102GLF

5

Any updates? I am kinda stuck at the moment.

6

Hi @pursley ,

Thanks for your patience. In order to use a potentiometer for feedback network, you will still need a fixed bottom resistor in place to set the current of the resistor divider:

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Give this a shot, let me know if it works.

Thanks,
Rubas