ADN2850BCPZ25-RL7 datasheet(20/30 Pages) AD

Part #	ADN2850BCPZ25-RL7

Description	Nonvolatile Memory, Dual 1024-Position Digital Resistor

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ADN2850

Data Sheet

Rev. F | Page 20 of 30

Using CS to Re-Execute a Previous Command

Another subtle feature of the ADN2850 is that a subsequent CS

strobe, without clock and data, repeats a previous command.

Using Additional Internal Nonvolatile EEMEM

The ADN2850 contains additional user EEMEM registers for

storing any 16-bit data such as memory data for other components,

look-up tables, or system identification information. Table 10 pro-

vides an address map of the internal storage registers shown in the

functional block diagram (see Figure 1) as EEMEM1, EEMEM2,

and 26 bytes (13 addresses × 2 bytes each) of User EEMEM.

Table 10. EEMEM Address Map

EEMEM No.

Address

EEMEM Content for …

1

0000

RDAC11

2

0001

RDAC2

3

0010

USER12

4

0011

USER2

…

15

1110

USER13

16

1111

RWB1 tolerance3

1 RDAC data stored in EEMEM locations is transferred to the corresponding

RDAC register at power-on, or when Instruction 1, Instruction 8, and PR are

executed.

2 USERx are internal nonvolatile EEMEM registers available to store and

retrieve constants and other 16-bit information using Instruction 3 and

Instruction 9, respectively.

3 Read only.

Calculating Actual End-to-End Terminal Resistance

The resistance tolerance is stored in the EEMEM register during

factory testing. The actual end-to-end resistance can, therefore,

be calculated, which is valuable for calibration, tolerance matching,

and precision applications. Note that this value is read only and

the RWB2 at full scale matches with RWB1at full scale, typically 0.1%.

The resistance tolerance in percentage is contained in the last

16 bits of data in EEMEM Register 15. The format is the sign

magnitude binary format with the MSB designate for sign

(0 = negative and 1 = positive), the next 7 MSB designate the

integer number, and the 8 LSB designate the decimal number

(see Table 12).

For example, if RWB_RATED = 250 kΩ and the data in the SDO

shows XXXX XXXX 1001 1100 0000 1111, RWB at full scale can

be calculated as follows:



MSB: 1 = positive



Next 7 LSB: 001 1100 = 28



8 LSB: 0000 1111 = 15 × 2−8 = 0.06



% tolerance = 28.06%

Therefore, RWB at full scale = 320.15 kΩ

RDAC STRUCTURE

The RDAC contains multiple strings of equal resistor segments

with an array of analog switches that acts as the wiper connection.

The number of positions is the resolution of the device. The

ADN2850 has 1024 connection points, allowing it to provide better

than 0.1% setability resolution. Figure 32 shows an equivalent

structure of the connections among the three terminals of the

RDAC. The SWB is always on, while the switches, SW(0) to

SW(2N − 1), are on one at a time, depending on the resistance

position decoded from the data bits. Because the switch is not

ideal, there is a 30 Ω wiper resistance, RW. Wiper resistance is a

function of supply voltage and temperature. The lower the supply

voltage or the higher the temperature, the higher the resulting

wiper resistance. Users should be aware of the wiper resistance

dynamics, if accurate prediction of the output resistance is needed.

SW(1)

SW(0)

SWB

B

RS

SW(2N – 1)

W

SW(2N – 2)

RDAC

WIPER

REGISTER

AND

DECODER

RS =RWB_NOMINAL/2N

RS

DIGITAL

CIRCUITRY

OMITTED FOR

CLARITY

Figure 32. Equivalent RDAC Structure

Table 11. Nominal Individual Segment Resistor Values

Device Resolution

25 kΩ

250 kΩ

1024-Step

24.4Ω

244Ω

Table 12. Calculating End-to-End Terminal Resistance

Bit

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

Sign

Mag

Sign

26

25

24

23

22

21

20

.

2−1

2−2

2−3

2−4

2−5

2−6

2−7

2−8

7 Bits for Integer Number

Decimal

Point

8 Bits for Decimal Number

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