AD5251 Analog Devices, AD5251 Datasheet - Page 14

• Manufacturer Part Number: AD5251
• Description: (AD5251 / AD5252) Dual 64-and 256-Position I2C Nonvolatile Memory Digital Potentiometers
• Manufacturer: Analog Devices

AD5251/AD5252
R
The AD5251/AD5252 feature patented R
the nonvolatile memory. The tolerance of each channel is stored
in the memory during the factory production and can be read
by users at any time. The knowledge of stored tolerance, which
is the average of R
to predict R
rheostat mode, and open-loop applications where knowledge of
absolute resistance is critical.
The stored tolerances reside in the read-only memory, and are
expressed as a percentage. The tolerance is stored in two
memory locations (see Table 10). The data format of the
tolerance is in sign magnitude binary form. An example is
shown in Figure 11. In the first memory location, the MSB is
designated for the sign (0 = + and 1= –) and the 7 LSBs are
designated for the integer portion of the tolerance. In the
second memory location, all eight data bits are designated for
the decimal portion of tolerance. As shown in Table 10 and
Figure 12 for example, if the rated R
readback from Address 11000 shows 0001 1100 and Address
11001 shows 0000 1111, then RDAC0 tolerance can be
calculated as
MSB: 0 = +
Next 7 MSB: 001 1100 = 28
8 LSB: 0000 1111 = 15 × 2
Tolerance = +28.06% and therefore
R
AB
AB_ACTUAL
Tolerance Stored in Read-Only Memory
= 12.806 kΩ
Figure 12. Format of Stored Tolerance in Sign Magnitude Format with Bit Position Descriptions. (Unit is percent. Only data bytes are shown.)
AB
accurately. This feature is valuable for precision,
AB
A
over all codes (see Figure 28), allows users
SIGN
SIGN
D7
–8
= 0.06
D6
2
6
7 BITS FOR INTEGER NUMBER
D5
2
5
AB
= 10 kΩ and the data
D4
2
4
AB
tolerances storage in
D3
2
3
D2
2
2
D1
2
1
D0
Rev. 0 | Page 14 of 28
2
0
A
EEMEM Write-Acknowledge Polling
After each write operation to the EEMEM registers, an internal
write cycle begins. The I
determine if the internal write cycle is complete and the I
interface is enabled, interface polling can be executed. I
interface polling can be conducted by sending a start condition
followed by the slave address + the write bit. If the I
responds with an ACK, the write cycle is complete and the
interface is ready to proceed with further operations. Other-
wise, I
Commands 2 and 7 also require acknowledge polling.
EEMEM Write Protection
Setting the WP pin to a logic LOW after EEMEM programming
protects the memory and RDAC registers from future write
operations. In this mode, the EEMEM and RDAC read
operations operate as normal. When write protection is
enabled, Command 1 (Restore from EEMEM to RDAC) and
Command 7 (Reset) function normally to allow RDAC settings
to be refreshed from the EEMEM to the RDAC registers.
2
D7
–1
D6
2
–2
2
C interface polling can be repeated until it succeeds.
8 BITS FOR DECIMAL NUMBER
2
D5
–3
2
D4
–4
2
D3
–5
2
C interface of the device is disabled. To
2
D2
–6
2
D1
–7
2
D0
–8
A
2
C interface
2
C
2
C