Data Sheet

AD5291/AD5292

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 12). Thereafter, the wiper position is always set at that

position for any future on-off-on power supply sequence. The

AD5291 and 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 verification.

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 68). Prior to 20-TP activation, the AD5291

and AD5292 preset to midscale on power-up.

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 13 and Table 14), 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 11). 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.

Table 12. Write and Read to RDAC and 20-TP Memory

DIN

SDO

Action

0x1803

0xXXXX

Enable update of wiper position and 20-TP memory contents through digital interface.

0x0500

0x1803

Write 0x100 to the RDAC register; wiper moves to ¼ full-scale position.

0x0800

0x0500

Prepare data read from the RDAC register.

0x0C00

0x0100

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).

0x1C00

0x0C00

Prepare data read from the control register.

0x0000

0x000X

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.

DB9

DB8

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

X

X

X

X

X

X

C3

C2

C1

C0

1

X = don’t care.

Table 14. Control Register Function

Bit Name

Description

C0

20-TP program enable

0 = 20-TP program disabled (default)

1 = enable device for 20-TP program

C1

RDAC register write protect

1 = allow update of wiper position through digital Interface

C2

Calibration enable

0 = resistor performance mode enabled (default)

1 = normal mode enabled

C3

20-TP memory program success

0 = fuse program command unsuccessful (default)

1 = fuse program command successful

1

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.

Rev. E | Page 23 of 30