Application Note 593: 2001 Digital Potentiometers: Frequently Ask

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Application Note 593: 2001 Digital Potentiometers: Frequently Ask

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CONVERSION/SAMPLING CIRCUITS DIGITAL POTENTIOMETERS
Application Note 593: 2001
Digital Potentiometers: Frequently Asked Questions
This application note answers frequently asked questions Dallas Semiconductor digital potentiometers. Subjects include audio characterization interface requirements.
What Noise Specification Digital Potentiometer?
Noise specs were removed from digital data sheets 1999. study Georgia Institute Technology, performed under supervision Professor P.E. Allen, DS1267, DS1666, DS1667, DS1669 were measured noise. conclusions this report were following: equivalent input noise voltage proportional resistance. test data input noise voltages greater than calculated thermal noise. This implies that other noise sources including test system noise, power supply noise, parasitic noise caused from board wiring coupled into system. There exists residual noise chips approximately10nv/sqrt(Hz) exists chips.
Want DS1669's Pushbutton Inputs Want Drive Them From Logic Board. What Problems Might Encounter?
order into 2-button mode, DS1669 requires inputs open-circuited power-up. With processor control, some logic gates will pull inputs enough activate input. open circuit effect accomplished with schottky diode between processor pointed toward processor, between ground controlled processor. Another option look DS1804, device designed processor connections. DS1669 single pushbutton mode anytime used, must tied directly power-up.
What Need Know About Input Dallastats?
When powered with input (connected Gnd), wiper will move from other back, continuously cycling down until input taken high high impedance since there internal pull-up), after which both pushbutton inputs input will operate correctly. (For example, input overrides pushbutton inputs power-up). other hand, when powered
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with input either open high (connected VCC), high-to-low transition input will move wiper until AFTER pushbutton inputs activated.
What Purpose Waiver DS1867-A3 (Lock-out Problem)?
prior DS1867 devices have power-down problem only shipped under waiver. Consult Note solve problem. device requires powerdown ramp time from 4.5V 3.0V least Faster ramp-down times cause position wipers stored correctly. Ramp-down slew rates 300700mS between 4.5V 3.0V have been identified causing permanent wiper storage problems, even after part been powered down correctly. Power supply glitches during power-down cause fast supply ramp, which will damage part. Normal decoupling practices should used near this device reduce risk fast transients from power supply other devices turning off. Large enough glitches during normal operation also cause this event happen.
MORE INFORMATION DS1267: QuickView DS1666: QuickView DS1669: QuickView DS1804: QuickView
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Application Note 593: 2001 Digital Potentiometers: Frequently Ask

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