Datasheet

Data Sheet AD5231
Rev. D | Page 19 of 28
Using Additional Internal Nonvolatile EEMEM
The AD5231 contains additional user EEMEM registers for
storing any 16-bit data such as memory data for other compo-
nents, look-up tables, or system identification information.
Table 9 provides an address map of the internal storage registers
shown in the functional block diagram as EEMEM1, EEMEM2,
and 28 bytes (14 addresses × 2 bytes each) of user EEMEM.
Table 9. EEMEM Address Map
Address EEMEM for…
0000 RDAC
1, 2
0001 O1 and O2
3
0010 USER1
4
0011 USER2
… …
1110 USER13
1111 USER14
1
RDAC data stored in EEMEM location is transferred to the RDAC register at
power-on, or when Instruction 1, Instruction 8, or
PR
are executed.
2
Execution of Instruction 1 leaves the device in the read mode power
consumption state. After the last Instruction 1 is executed, the user should
perform a NOP, Instruction 0 to return the device to the low power idling
state.
3
O1 and O2 data stored in EEMEM locations is transferred to the
corresponding digital register at power-on, or when Instruction 1 and
Instruction 8 are executed.
4
USERx are internal nonvolatile EEMEM registers available to store 16-bit
information using Instruction 3 and restore the contents using Instruction 9.
RDAC STRUCTURE
The patent-pending RDAC contains multiple strings of equal
resistor segments with an array of analog switches that act as the
wiper connection. The number of positions is the resolution of
the device. The AD5231 has 1024 connection points, allowing it
to provide better than 0.1% settability resolution. Figure 43
shows an equivalent structure of the connections among the
three terminals of the RDAC. The SW
A
and SW
B
are always on,
while the switches SW(0) to SW(2
N
−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 15 Ω wiper
resistance, R
W
. 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)
SW
B
B
SW
A
SW(2
N
–1)
SW(2
N
–2)
A
W
R
S
R
S
R
S
R
S
= R
AB
/2
N
DIGITAL
CIRCUITRY
OMITTED FOR
CLARITY
RDAC
WIPER
REGISTER
AND
DECODER
02739-042
Figure 43. Equivalent RDAC Structure (Patent Pending)
Table 10. Nominal Individual Segment Resistor (R
S
)
Device
Resolution
10 kΩ
Version
50 kΩ
Version
100 kΩ
Version
10-Bit 9.8 Ω 48.8 Ω 97.6 Ω
PROGRAMMING THE VARIABLE RESISTOR
Rheostat Operation
The nominal resistance of the RDAC between Terminal A and
Terminal B, R
AB
, is available with 10 kΩ, 50 kΩ, and 100 kΩ
with 1024 positions (10-bit resolution). The final digit(s) of the
part number determine the nominal resistance value, for
example, 10 kΩ = 10; 50 kΩ = 50; 100 kΩ = C.
The 10-bit data-word in the RDAC latch is decoded to select
one of the 1024 possible settings. The following discussion
describes the calculation of resistance R
WB
at different codes of a
10 kΩ part. For V
DD
= 5 V, the wiper’s first connection starts at
Terminal B for data 0x000. R
WB
(0) is 15 Ω because of the wiper
resistance, and because it is independent of the nominal
resistance. The second connection is the first tap point where
R
WB
(1) becomes 9.7 Ω + 15 Ω = 24.7 Ω for data 0x001. The
third connection is the next tap point representing R
WB
(2) =
19.4 Ω + 15 Ω = 34.4 Ω for data 0x002 and so on. Each LSB data
value increase moves the wiper up the resistor ladder until the
last tap point is reached at R
WB
(1023) = 10,005 Ω. See Figure 43
for a simplified diagram of the equivalent RDAC circuit. When
R
WB
is used, Terminal A can be left floating or tied to the wiper.