AD5171

Rev. D | Page 12 of 24

THEORY OF OPERATION

SDA

SCL

A

W

B

COMPARATOR

MUX

DECODER

FUSES

EN

FUSE

REG.

DAC

REG.

ONE-TIME

PROGRAM/TEST

CONTROL BLOCK

Figure 25. Detailed Functional Block Diagram

The AD5171 allows unlimited 6-bit adjustments, except for the

one-time programmable, set-and-forget resistance setting. OTP

technology is a proven, cost-effective alternative over EEMEM

in one-time memory programming applications. The AD5171

employs fuse link technology to achieve the memory retention

of the resistance setting function. It has six data fuses that control

the address decoder for programming the RDAC, one user

mode test fuse for checking setup error, and one programming

lock fuse for disabling any further programming once the data

fuses are blown.

ONE-TIME PROGRAMMING (OTP)

Prior to OTP activation, the AD5171 presets to midscale during

initial power-on. After the wiper is set at the desired position,

the resistance can be permanently set by programming the T bit

high along with the proper coding (see Table 8 and Table 9) and

and 5.25 V to blow the fuses to achieve a given nonvolatile

operation. As a result, a system supply that is lower than 4.75 V

requires external supply for OTP. In addition, the user is only

allowed one attempt in blowing the fuses. If the user fails to

blow the fuses at the first attempt, the fuse structures may change

so that they may never be blown regardless of the energy applied

at subsequent events. For details, see the Power Supply

Considerations section.

The device control circuit has two validation bits, E1 and E0,

that can be read back to check the programming status (see

Table 5). Users should always read back the validation bits to

ensure that the fuses are properly blown. After the fuses are

blown, all fuse latches are enabled upon subsequent power-on;

therefore, the output corresponds to the stored setting.

Table 5. Validation Status

E1

E0

Status

0

0

Ready for programming.

0

1

Test fuse not blown successfully. For factory setup

checking purpose only. Users should not see these

combinations.

1

0

Fatal error. Some fuses are not blown. Do not retry.

Discard the unit.

1

1

Successful. No further programming is possible.

This section discusses the fuse operation in detail. When the

OTP T bit is set, the internal clock is enabled. The program then

attempts to blow a test fuse. The operation stops if the test fuse

is not properly blown. The validation bits, E1 and E0, show 01.

This status is intended for factory setup checking purposes

only; users should not see this status. If the test fuse is properly

blown, the data fuses can be programmed. The six data fuses

are programmed in six clock cycles. The output of the fuses is

compared with the code stored in the RDAC register. If they do

not match, E1 and E0 of 10 are issued as fatal errors and the

operation stops. Users should never try blowing the fuses more

than once because the fuse structure may have changed prohibiting

further programming. As a result, the unit must be discarded.

This error status can also occur if the OTP supply voltage goes

current is limited, or both the voltage and current ramp times

are slow. If the output and stored code match, the programming

lock fuse is blown so that no further programming is possible.

In the meantime, E1 and E0 issue 11, indicating the lock fuse is

properly blown. All the fuse latches are enabled at power-on;

therefore, from this point on, the output corresponds to the

stored setting. Figure 25 shows a detailed functional block

diagram.