AD5220 datasheet(12/16 Pages) AD

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REV. B

AD5200/AD5201

–12–

RDAC

LATCH &

DECODER

SHDN

SWSHDN

SW2N 1

SW2N 2

SW1

SW0

DIGITAL CIRCUITRY

OMITTED FOR CLARITY

RAB

2N–1

Figure 2a. AD5200 Equivalent RDAC Circuit. 255 positions

can be achieved up to Switch SW 2

–1.

SW2N 1

RDAC

LATCH &

DECODER

SW2N 2

SW1

SW0

DIGITAL CIRCUITRY

OMITTED FOR CLARITY

SHDN

SWSHDN

SW2N

RAB

Figure 2b. AD5201 Equivalent RDAC Circuit. Unlike AD5200,

33 positions can be achieved all the way to Switch SW 2

The general equation determining the digitally programmed

output resistance between W and B is:

() =+

255

Ω

for AD5200

(1)

() =+

Ω

for AD5201

(2)

where:

is the decimal equivalent of the data contained in

RDAC latch.

RAB is the nominal end-to-end resistance.

RW is the wiper resistance contributed by the on-resistance

of the internal switch.

Note D in AD5200 is between 0 to 255 for 256 positions. On

the other hand, D in AD5201 is between 0 to 32 so that 33

positions can be achieved due to the slight internal structure

difference, Figure 2b.

Again if RAB = 10 k

Ω and A terminal can be opened or tied to

W, the following output resistance between W to B will be set

for the following RDAC latch codes:

AD5200 Wiper-to-B Resistance

DRWB

(DEC)

( )

Output State

255

10050

Full-Scale (RAB + RW)

128

5070

Midscale

189

1 LSB

Zero-Scale (Wiper Contact Resistance)

AD5201 Wiper-to-B Resistance

DRWB

(DEC)

( )

Output State

10050

Full-Scale (RAB + RW)

5050

Midscale

363

1 LSB

Zero-Scale (Wiper Contact Resistance)

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

Ω is present. Care should be taken to limit the current flow

between W and B in this state to no more than

±20 mA to avoid

degradation or possible destruction of the internal switch contact.

Like the mechanical potentiometer the RDAC replaces, it is

totally symmetrical. The resistance between the wiper W and

Terminal A also produces a digitally controlled resistance RWA.

When these terminals are used, the B terminal should be tied to

the wiper. Setting the resistance value for RWA starts at a maxi-

mum value of resistance and decreases as the data loaded in

the latch is increased in value. The general equation for this

operation is:

() =

−

()

255

Ω

for AD5200

(3)

() =

−

()

Ω

for AD5201

(4)

Similarly, D in AD5200 is between 0 to 255, whereas D in

AD5201 is between 0 to 32.

For RAB = 10 k

Ω and B terminal is opened or tied to the wiper

W, the following output resistance between W and A will be set

for the following RDAC latch codes:

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