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Re: bipolar digital pot
by Spehro Pefhany
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Quoting Martin <martin@...>:
> I have an analog circuit that has a (normally) negative polarity DC
> feedback signal. I'd like to change the gain of the circuit digitally,
> so I'd like to use a digital pot. The problem is that a digital pot can
> only take signals between VEE and VDD - most usually probably 0v to 5v.
>
> My rails are +5/0/-5 and my feedback lies somewhere between 0 and -5.
> Has anyone encountered a digital pot that can either take a 10v supply,
> or has level shifters on the digital lines? I think I might be able to
> use a CD4052 with discrete resistors, but then it's a 16 pin chip I have
> to put on the board.
>
> Any ideas?
There do exist digital pots which will operate from +/-5V supplies, with
level shifting for the digital bits. AD is one supplier, but they tend
to be more expensive (and higher performance!) than the low end ones. There
might be other suppliers with similar products, but I'm not aware of
any offhand.
Eg. http://www.analog.com/UploadedFiles/Data_Sheets/AD5290.pdf
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
s...@... Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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> I have an analog circuit that has a (normally) negative polarity DC
> feedback signal. I'd like to change the gain of the circuit digitally,
> so I'd like to use a digital pot. The problem is that a digital pot can
> only take signals between VEE and VDD - most usually probably 0v to 5v.
>
> My rails are +5/0/-5 and my feedback lies somewhere between 0 and -5.
> Has anyone encountered a digital pot that can either take a 10v supply,
> or has level shifters on the digital lines? I think I might be able to
> use a CD4052 with discrete resistors, but then it's a 16 pin chip I have
> to put on the board.
>
> Any ideas?
There do exist digital pots which will operate from +/-5V supplies, with
level shifting for the digital bits. AD is one supplier, but they tend
to be more expensive (and higher performance!) than the low end ones. There
might be other suppliers with similar products, but I'm not aware of
any offhand.
Eg. http://www.analog.com/UploadedFiles/Data_Sheets/AD5290.pdf
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
s...@... Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
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