digital potentiometer

aconz2

I was wondering about the AD5220.

http://www.parallax.com/Portals/0/Downloads/docs/prod/compshop/AD5220.pdf

I am having a hard time interpreting the datasheet whether or not this can be used as a current limiting resistor (between power and load) for around 9 v and 100mA. If it cannot be used this way, I saw another article that uses the variable resistance applied to a transistor that would then dim an LED.
Thanks

Mike Green

This cannot be used as a current limiting resistor at the voltage and current you indicated. You cannot apply more than 7V to it and the lowest full scale resistance is 10K. The wiper resistance is around 40 Ohms, so even at the zero position, you'd have that much resistance. The datasheet doesn't even mention a maximum current, so I suspect it's on the order of a few milliAmps at most. You'd have to use a transistor or op-amp amplifier to control the current to something. You could also use a transistor or op-amp with the PWM statement to provide a variable current supply. For dimming LEDs you could also use the PWM statement and a switching transistor for dimming. Read the section of the BASIC Stamp Syntax and Reference Manual on the PWM statement for more information.

Franklin

Looks like 7v 20ma

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- Stephen

Campeck

My ad5220 datasheet said no more than 5ma. after I put 20ma through it.

Franklin

Campeck, where did you find that?

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- Stephen

Campeck

On page 8 of 10 of the datasheet here:
http://www.analog.com/static/imported-files/data_sheets/AD5220.pdf

on the right side of the page under programming the variable resistor. bottom of paragraph one.

Care should be taken to limit
the current flow between W and B in the direct contact state to
a maximum value of 5 mA to avoid degradation or possible destruction
of the internal switch contact.