LT3090 and TPL0102; problem with the reference-current-set-pin of the LT3090

[AntoninoP]

I have an LT3090 LDO, and I use the TPL0102 (0-100 k) digital potentiometer to set the LDO resistence that varies the voltage output of the LT3090.

The LT3090 functioning is very simply: on the "set pin" there is a reference current of 50uA, and by changing the resistor I obtain the desired output voltage (Vout = 50uA * Rset).

The problem is: when I apply low values of resistence (0-10 k), the reference current (50uA) is maintained and is stable. When I apply high values of resistence (10-100 k), the reference current descends and the output voltage remains constant even if the resistance value increase.

This fact did not happen if I substitute the digital potentiometer with a normal resistor.

I hope you can help me.
Thanks,
Antonino

 

[FvM]

Are you considering the fact that resistor terminal voltage must be inside the Vss to Vdd range? Means a 0..-5 negative regulator needs Vss =-5, Vdd = 0V and level shift for the control inputs.