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MCP41HVx1 anyone?

Dear All,

Does anyone have any experience in using one of this digital pot from this Microchip family?

My project requires that I control a voltage divider from the computer, so i'm using an Arduino to control an MCP41HV51 digital pot via SPI. I'm able to control it, no problem, thanks to Greg Srabian's library. I can program the wiper position and see the resulting resistance changing on my ohmmeter .

What I can't figure out, from reading the datasheet, is how to connect the analog side power pins and to those to the potentiometer (eventually).

So, my voltage divider must be between GND and -10V. I have available on my system +13V, +5V and -10V. I was thinking to connect V+ to GND; V- to -10; one side of the potentiometer to GND; the other to -10V. Is this correct? I would be more comfortable if could just apply 0 and -10V to the end termi nals of the potentiometer and power the analog part of the chip from the +1

3V ps, but i'm not sure this would work....

I guess what is unclear to me is the relation (if any) between the voltage on the V+ and V- pins and the voltage at the potentiometer end terminals.

Any suggestions would be very welcomed, thank you very much!

Regards jmariano

Reply to
jmariano
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The logic supply VL and the ground pin have to be between V+ and V-, so if you ground V+ and VL you'll have to make another rail for the ground pin, and you'll have to level-shift the SPI.

That's not that hard to do, but with a 36V part there's no reason to.

I'd use

V+ -> +13 VL -> +5 GND -> 0V V- -> -10

You can also use +5 for V+, but I suspect it's probably a noisier rail.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com
Reply to
Phil Hobbs

his Microchip family?

so i'm using an Arduino to control an MCP41HV51 digital pot via SPI. I'm a ble to control it, no problem, thanks to Greg Srabian's library. I can prog ram the wiper position and see the resulting resistance changing on my ohmm eter..

the analog side power pins and to those to the potentiometer (eventually).

n my system +13V, +5V and -10V. I was thinking to connect V+ to GND; V- to

-10; one side of the potentiometer to GND; the other to -10V.

erminals of the potentiometer and power the analog part of the chip from th e +13V ps, but i'm not sure this would work....

age on the V+ and V- pins and the voltage at the potentiometer end terminal s.

Hello Phil,

Thanks for your help, understood! I don't want to push my luck, but how about the relation between the voltag es at the potentiometer ends (P0A and P0B) and V+ and V-? P0A and P0B must also be between V+ and V-? That means that for my purposes I can use V+ -> +13 VL -> +5 GND -> 0V -> P0A V- -> -10 -> P0B Is that it?

Regards

jmariano

Reply to
jmariano

How did you reach that conclusion? (I'm not saying it's wrong or right here.)

I suggest reading the datasheet carefully yourself, and thinking about how the chips actually work. That's a bit harder these days because datasheets have become marketing documents rather than engineering ones, but there are certain regularities that you'll learn as you go along.

There are chips that work fine with their inputs way outside the supply rails, but they're rare.

Old ones, such as the LM324/358/339 family, often have useful properties accidentally. Those ones have lateral PNP input transistors without protection diodes, so they'll survive having their inputs pulled as high as 35V from the negative supply even if the positive supply is much lower. (Of course if both inputs are outside the positive common mode limit the chip doesn't work properly, but it doesn't die.)

For newer ones they usually trumpet such things, e.g 'Beyond The Rails' op amps.

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510

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Reply to
Phil Hobbs

Wire the potentiometer pins like you would any potentiometer. So, you have it right: one side of the pot to GND, the other to -10. The output of the divider is the wiper pin of the pot.

Be aware that this is a low current potentiometer.

Ed

Reply to
ehsjr

his Microchip family?

so i'm using an Arduino to control an MCP41HV51 digital pot via SPI. I'm a ble to control it, no problem, thanks to Greg Srabian's library. I can prog ram the wiper position and see the resulting resistance changing on my ohmm eter.

the analog side power pins and to those to the potentiometer (eventually).

n my system +13V, +5V and -10V. I was thinking to connect V+ to GND; V- to

-10; one side of the potentiometer to GND; the other to -10V.

erminals of the potentiometer and power the analog part of the chip from th e +13V ps, but i'm not sure this would work....

age on the V+ and V- pins and the voltage at the potentiometer end terminal s.

Good evening,

I took Phil's advice and read the data sheet carefully, again. Oh, boy, tho se things are hard to read, or maybe my English is not that good, but it se ams that everything is there except what you are looking for... Anyway, is not easy to figure out how the chip works, because not many details are gi ven about the inner structure of the chip, but from what I as able to under stand, the voltage difference between the potentiometer terminals A and B, what they call the Resistor Network Supply Voltage, must be between V- and V+. Tomorrow I will give it a try. Thank you Phil and Ed for taking the time to help me. Regards jmariano

Reply to
jmariano

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