ADN2860 查看數據表（PDF） - Analog Devices

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ADN2860

3-Channel Digital Potentiometer with Nonvolatile Memory

Analog Devices 

ADN2860

For RDAC0 and RDAC1:

RWB

(D)

=

D

512

×

RAB

+

RW

(1)

For RDAC2:

RWB

(D)

=

D

128

×

RAB

+

RW

(2)

where:

D is the decimal equivalent of the data contained in the RDAC

register.

RW is the wiper resistance.

The output resistance values in Table 11 are set for the given

RDAC latch codes with VDD = 5 V, which applies to RAB = 25 kΩ

digital potentiometers.

Table 11. RWB at Selected Codes for RWB_FS = 25 kΩ

D (DEC) RWB(d) (Ω) Output State

511

25051

Full scale

256

12600

Midscale

1

148.8

1 LSB

0

100

Zero scale (wiper contact resistance)

Note that in the zero-scale condition, a finite wiper resistance of

100 Ω is present. To avoid degradation or possible destruction

of the internal switches, care should be taken to limit the current

flow between Terminals W and B to no more than 20 mA

intermittently or 2 mA continuously.

Channel-to-channel RWB matching is better than 0.1%. The

change in RWB with temperature has a 35 ppm/°C temperature

coefficient.

Like the mechanical potentiometer that the RDAC replaces, the

ADN2860 parts are totally symmetrical. The resistance between

the W wiper and the A terminal also produces a digitally con-

trolled complementary resistance, RWA. When RWA is used, the

B terminal can be floating or tied to the wiper. Setting the

resistance value for RWA starts at a maximum value of resistance

and decreases as the data loaded in the latch is increased in

value. The general transfer equations for this operation are as

follows:

For RDAC0 and RDAC1:

RWB

(D) =

512 − D

512

× RAB

+

RW

(3)

For RDAC2:

RWB

(D)

=

128 − D

128

×

RAB

+

RW

(4)

For example, the following RDAC latch codes set the

corresponding output resistance values, which apply to

RAB = 25 kΩ digital potentiometers.

Table 12. RWA(d) at Selected Codes for RAB = 25 kΩ

D (DEC)

RWA(d) (Ω)

Output State

511

148.8

Full scale

256

12600

Midscale

1

25051

1 LSB

0

25100

Zero scale

The typical distribution of RAB from channel to channel is ±0.1%

within the same package. Device-to-device matching is lot

dependent, with a worst-case variation of ±15%. RAB temp-

erature coefficient is 35 ppm/°C.

PROGRAMMING THE POTENTIOMETER DIVIDER

Voltage Output Operation

The digital potentiometer can be configured to generate an

output voltage at the wiper terminal, which is proportional to

the input voltages applied to the A and B terminals. Connecting

the A terminal to 5 V and the B terminal to ground produces an

output voltage at the wiper that can vary between 0 V to 5 V.

Each LSB of voltage is equal to the voltage applied across the A

and B terminals divided by the 2N position resolution of the

potentiometer divider.

Since the ADN2860 can operate from dual supplies, the general

equations defining the output voltage at VW with respect to

ground for any given input voltages applied to the A and B

terminals are as follows:

For RDAC0 and RDAC1:

VW

(D) =

D

512

× VAB

+ VB

(5)

For RDAC2:

VW

(D) =

D

128

× VAB

+ VB

(6)

Equation 5 assumes that VW is buffered to null the effect of

wiper resistance. Operation of the digital potentiometer in the

divider mode results in more accurate operation over

temperature. In this mode, the output voltage is dependent on

the ratio of the internal resistors, not on the absolute value;

therefore, the drift improves to 15 ppm/°C. There is no voltage

polarity restriction between the A, B, and W terminals as long

as the terminal voltage (VTERM) stays within VSS < VTERM < VDD.

Rev. A | Page 18 of 20

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