DS1881 Digital Pot Volume Control

[tma]

Greetings,

Does anyone here have experience with the DS1881 audio taper digital dual pot? I would like to discuss biasing options for the analog section. Specifically I would like to know if anyone has tried a circuit in which the low ends of the pots are connected directly to ground instead of being connected to half VCC.

Thanks in advance for any helpful info!

tma

 

[sgrossklass]

ABSOLUTE MAXIMUM RATINGS
[...]
Voltage on H1, H0, W1, W0, L1, and L0 Relative
to GND...............................................................-0.5V to +6.0V

Sounds like this part is not suitable for what you are trying to do - AC coupling will be unavoidable. You would need one that can accept an analog split supply, and possibly at least +/-5 V, too (so 2 Vrms input will be accepted without issue). (You can't run this one split supply because of the digital I/O, unlike e.g. a self-contained part like the MAX5486.) Maybe look at PGAs instead of digipots, too.

 

[Neil Davis]

I've used the DS1807, which is similar. You can tie the lower end of the pot to ground, but then you need to AC couple the other pins. The attachment shows the schematic where the device was wired both ways -- one with a 2.5V reference and the other with ground as the reference.

 

[stratus46]

I'm not sure of what you're trying to do but this may help.

https://www.analog.com/media/en/new...ection-guide/Choosing_the_Correct_Digipot.pdf

I've never been a big fan of Maxim as they tended to be overoptimistic in that the chips were slightly lacking. Analog devices OTOH tend to under promise. I've use many ADI chip in projects and all performed beyond expectations. Only once did I have to contact engineering support and he was very helpful. Their chips always work as the data sheet claims. Yes, they're more expensive but for something that is sure to work, it's worth it to me.

G²

 

[Rick PA Stadel]

You might want to take a quick look at the DS1882. Its identical except for Pin 4 -- on the -81 it is NC; on the -82 its the negative power supply.

Remembering that the signals you want to control travel both above and below a mid point, using the -81 without a Vcc/2 or something like it will chop off the negative excursions.

Sorry, but the only choices are bi-polar supplies, or a virtual ground.

Regards,
Rick

 

[tma]

I've used the DS1807, which is similar. You can tie the lower end of the pot to ground, but then you need to AC couple the other pins. The attachment shows the schematic where the device was wired both ways -- one with a 2.5V reference and the other with ground as the reference.

Greetings Again,

Thanks to all those that replied! Nice to hear that I can ground the low end as long as I use AC coupling. I wonder if I would be able to use DC coupling to the top end of the pot with the low end grounded? The quiescent bias on the top end would be mid rail and the signal level less than 1 V ptp?

The wiper would DC couple to a rail-to-rail voltage follower with an AC coupled output. The quiescent voltage on the tap would get very close to ground potential for low tap settings but the signal swing would be proportionally lower thus should not swing below ground level.

The maximum ptp audio swing on one of the pots would only be about 300 mV thus it should well away from the rails with the expected steady 2.5V quiescent DC level. All the associated op amps are rail-to-rail.

What had me wondering was if the 2.5V reference was required for biasing the tap switches. I must admit I am having difficulty imagining how those tap switches get biased without loading the tap positions - nice MOSFET magic I presume.

The only example in the DS1881 data sheet shows the low end connected to VCC/2 reference. I now presume that is just done for biasing the connected opamps mid rail. The second pot section will be exposed to about 2V ptp signal level but it is easy for me to bias it with a 2.5V reference.

If the analog pot section of the DS1881 behaves like a conventional pot with the low end grounded with the exceptions of rail limitations and wiper resistance, etc that should work for my circuit.

I also like the Analog Devices products and have had good success using them. But the 1dB per step feature of the DS1881 is a good fit for this application and the price is right. As long as the Dallas Semiconductor specs are reasonably close it should work OK for what I wish to do.

Thanks Again!
tma

 

[vzaichenko]

For connecting directly to ground you just need DS1882 (+/-5V supplies).

Cheers,
Valery

P.S. Oops - sorry, missed the post #5 by Rick