AD5292 Analog Devices, AD5292 Datasheet - Page 19

• Manufacturer Part Number: AD5292
• Description: (AD5291 / AD5292) Digital Potentiometer
• Manufacturer: Analog Devices

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20-TP MEMORY
Once a desirable wiper position is found, the contents of the
RDAC register can be saved into a 20-TP memory register
(see Table 10). Thereafter, the wiper position is always set at that
position for any future on-off-on power supply sequence. The
AD5291/AD5292 have an array of 20 one-time programmable
(OTP) memory registers. When the desired word is programmed
to 20-TP memory, the device automatically verifies that the
program command was successful. The verification process
includes margin testing. Bit C3 of the control register can be
polled to verify that the fuse program command was successful.
Programming data to 20-TP memory consumes approximately
25 mA for 550 μs, and takes approximately 8 ms to complete.
During this time, the shift register is locked, preventing any
changes from taking place. The RDY pin can be used to monitor
the completion of the 20-TP memory program and for verifica-
tion. No change in supply voltage is required to program the
20-TP memory. However, a 1 μF capacitor on the EXT_CAP pin
is required (see Figure 47). Prior to 20-TP activation, the AD5291/
AD5292 preset to midscale on power-up.
Table 10. Write and Read to RDAC and 20-TP Memory
DIN
0x1803
0x0500
0x0800
0x0C00
0x1C00
0x0000
Table 11. Control Register Bit Map
DB9
X
1
Table 12. Control Register Description
Bit Name
C0
C1
C2
C3
1
X = don’t care.
Wiper position frozen to value last programmed in 20-TP memory. Wiper is frozen to midscale if 20-TP memory has not been previously programmed.
SDO
0xXXXX
0x1803
0x0500
0x0100
0x0C00
0x000X
X
DB8
Description
20-TP program enable
0 = 20-TP program disabled (default)
1 = enable device for 20-TP program
RDAC register write protect
0 = wiper position frozen to value in memory (default)
1 = allow update of wiper position through digital Interface
Calibration enable
0 = resistor performance mode enabled (default)
1 = normal mode enabled
20-TP memory program success
0 = fuse program command unsuccessful (default)
1 = fuse program command successful
Action
Enable update of wiper position and 20-TP memory contents through digital interface.
Write 0x100 to the RDAC register; wiper moves to ¼ full-scale position.
Prepare data read from the RDAC register.
Stores RDAC register content into 20-TP memory. The 16-bit word appears out of SDO, where the last 10 bits
contain the contents of the RDAC register (0x100).
Prepare data read from the control register.
NOP Instruction 0 sends 16-bit word out of SDO, where the last four bits contain the contents of the control
register. If Bit C3 = 1, the fuse program command is successful.
DB7
X
1
DB6
X
DB5
X
Rev. 0 | Page 19 of 28
DB4
X
WRITE PROTECTION
On power-up, the shift register write commands for both the
RDAC register and the 20-TP memory register are disabled.
The RDAC write protect bit, C1 of the control register (see
Table 11 and Table 12), is set to 0 by default. This disables any
change of the RDAC register content regardless of the software
commands, except that the RDAC register can be refreshed
from the 20-TP memory using the software reset command
(Command 4) or through hardware by the RESET pin. To enable
programming of the variable resistor wiper position (program-
ming the RDAC register), the write protect bit, C1 of the control
register, must first be programmed. This is accomplished by
loading the shift register with Command 6 (see Table 9). To
enable programming of the 20-TP memory block bit, C0 of the
control register (set to 0 by default) must first be set to 1.
1
DB3
C3
DB2
C2
AD5291/AD5292
DB1
C1
DB0
C0