AD5235BRU25 Analog Devices Inc, AD5235BRU25 Datasheet - Page 21

• Manufacturer Part Number: AD5235BRU25
• Description: IC POT DUAL 25K 1024POS 16-TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD5235BRU25

• Rohs Status: RoHS non-compliant
• Taps: 1024
• Resistance (ohms): 25K
• Number Of Circuits: 2
• Temperature Coefficient: 35 ppm/°C Typical
• Memory Type: Non-Volatile
• Interface: 4-Wire SPI Serial
• Voltage - Supply: 3 V ~ 5.5 V, ±2.25 V ~ 2.75 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP
• Resistance In Ohms: 25K
• End To End Resistance: 25kohm
• Track Taper: Logarithmic
• Resistance Tolerance: ± 30%
• No. Of Steps: 1024
• Supply Voltage Range: 3V To 5.5V, ± 2.25V To ± 2.75V
• Control Interface: Serial, SPI
• For Use With: EVAL-AD5235EBZ - BOARD EVALUATION FOR AD5235
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Using CS to Re-Execute a Previous Command
Another subtle feature of the AD5235 is that a subsequent CS
strobe, without clock and data, repeats a previous command.
Using Additional Internal Nonvolatile EEMEM
The AD5235 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 9 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 9. EEMEM Address Map
EEMEM No.
1
2
3
4
…
15
16
1
2
3
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 R
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 11).
Table 11. Calculating End-to-End Terminal Resistance
Bit
Sign
Mag
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.
USERx are internal nonvolatile EEMEM registers available to store and
retrieve constants and other 16-bit information using Instruction 3 and
Instruction 9, respectively.
Read only.
AB2
D15
Sign
matches with R
D14
2
6
Address
0000
0001
0010
0011
…
1110
1111
D13
2
AB1
5
, typically 0.1%.
7 Bits for Integer Number
D12
2
4
EEMEM Content for …
RDAC1
RDAC2
USER1
USER2
…
USER13
R
AB1
tolerance
D11
2
3
2
1
D10
2
2
3
2
D9
1
Rev. D | Page 21 of 32
D8
2
0
Decimal
Point
.
For example, if R
shows XXXX XXXX 1001 1100 0000 1111, R
calculated as follows:
RDAC STRUCTURE
The patent-pending 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 AD5235 has 1024 connection points, allowing it to
provide better than 0.1% setability resolution. Figure 45 shows
an equivalent structure of the connections among the three
terminals of the RDAC. The SW
the switches, SW(0) to SW(2
on the resistance position decoded from the data bits. Because
the switch is not ideal, there is a 50 Ω wiper resistance, R
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.
Table 10. Nominal Individual Segment Resistor Values
Device Resolution
1024-Step
MSB: 1 = positive
Next 7 LSB: 001 1100 = 28
8 LSB: 0000 1111 = 15 × 2
% tolerance = 28.06%
Therefore, R
D7
2
−1
D6
2
−2
DIGITAL
CIRCUITRY
OMITTED FOR
CLARITY
R
Figure 45. Equivalent RDAC Structure
AB_RATED
AB_ACTUAL
REGISTER
S
DECODER
= R
WIPER
RDAC
AND
D5
2
AB
−3
/2
8 Bits for Decimal Number
N
= 250 kΩ and the data in the SDO
= 320.15 kΩ
N
− 1), are on one at a time, depending
D4
2
R
R
R
−4
S
S
S
−8
A
= 0.06
SW(2
and SW
SW(2
SW
SW
25 kΩ
24.4
SW
SW
D3
2
N –
−5
(1)
(0)
N –
A
B
2)
1)
B
are always on, while
D2
2
W
A
B
AB_ACTUAL
−6
250 kΩ
244
AD5235
D1
2
−7
can be
W
.
D0
2
−8