MCP41HVx1 anyone?

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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

Re: MCP41HVx1 anyone?
On 2020-09-25 16:19, jmariano wrote:
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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
We've slightly trimmed the long signature. Click to see the full one.
Re: MCP41HVx1 anyone?
On Friday, 25 September 2020 at 21:35:27 UTC+1, Phil Hobbs wrote:
Quoted text here. Click to load it
his Microchip family?  
Quoted text here. Click to load it
 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..
Quoted text here. Click to load it
the analog side power pins and to those to the potentiometer (eventually).
  
Quoted text here. Click to load it
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.  
Quoted text here. Click to load it
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....  
Quoted text here. Click to load it
age on the V+ and V- pins and the voltage at the potentiometer end terminal
s.  
Quoted text here. Click to load it
  
Quoted text here. Click to load it
  
Quoted text here. Click to load it
  
Quoted text here. Click to load it

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  
  

Re: MCP41HVx1 anyone?
On 2020-09-25 18:22, jmariano wrote:
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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

http://electrooptical.net
http://hobbs-eo.com


Re: MCP41HVx1 anyone?
On 9/25/2020 4:19 PM, jmariano wrote:
Quoted text here. Click to load it

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

Re: MCP41HVx1 anyone?
On Sunday, 27 September 2020 at 07:03:39 UTC+1, ehsjr wrote:
Quoted text here. Click to load it
his Microchip family?  
Quoted text here. Click to load it
 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.  
Quoted text here. Click to load it
the analog side power pins and to those to the potentiometer (eventually).
  
Quoted text here. Click to load it
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.  
Quoted text here. Click to load it
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....  
Quoted text here. Click to load it
age on the V+ and V- pins and the voltage at the potentiometer end terminal
s.  
Quoted text here. Click to load it

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  

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