ad5171 Analog Devices, Inc., ad5171 Datasheet - Page 12

• Manufacturer Part Number: ad5171
• Description: 64-position Otp Digital Potentiometer
• Manufacturer: Analog Devices, Inc.

AD5171
THEORY OF OPERATION
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 pro-
gramming 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 7 and Table 8) and
one-time V
family of digital potentiometers requires V
5.25 V and 5.5 V to blow the fuses to achieve a given nonvolatile
setting. On the other hand, V
operation. As a result, system supply that is lower than 5.25 V
requires external supply for one-time programming. Also, the
user is allowed only 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 4). Users should always read back the validation bits to
ensure that the fuses are properly blown. After the fuses have
been blown, all fuse latches are enabled upon subsequent
power-on; therefore, the output corresponds to the stored
setting.
Table 4. Validation Status
E1
0
0
1
1
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, Bit E1 and Bit E0,
show 01. This status is intended for factory setup checking
purposes only; users should not see this status. If the test fuse is
E0
0
1
0
1
DD_OTP
Status
Ready for programming.
Test fuse not blown successfully. For factory
setup checking purpose only. Users should not
see these combinations.
Fatal error. Some fuses are not blown. Do not
retry. Dicard the unit.
Successful. No further programming is possible.
. The fuse link technology of the AD517x
DD
can be 2.7 V to 5.5 V during
DD_OTP
between
Rev. B | Page 12 of 24
properly blown, then 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
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 above or drops below the V
ment, the OTP supply 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 24 shows a
detailed functional block diagram.
SDA
POWER SUPPLY CONSIDERATIONS
To minimize the package pin count, both the one-time pro-
gramming and normal operating voltage supplies share the
same V
link technology that requires 5.25 V to 5.5 V for blowing the
internal fuses to achieve a given setting, but normal V
anywhere between 2.7 V and 5.5 V after the fuse programming
process. As a result, dual voltage supplies and isolation are
needed if system V
fuse programming supply (either an on-board regulator or
rack-mount power supply) must be rated at 5.25 V to 5.5 V and
able to provide a 100 mA current for 400 ms for successful one-
time programming. Once fuse programming is complete, the
V
2.7 V to 5.5 V; the device then consumes current in the µA
range. Figure 25 shows the simplest implementation to meet the
dual-voltage requirement with a jumper. This approach saves
one voltage supply, but draws additional current and requires
manual configuration.
SCL
DD_OTP
DD
supply must be removed to allow normal operation at
terminal of the AD5171. The AD5171 employs fuse
CONTROL BLOCK
PROGRAM/TEST
I
2
C INTERFACE
Figure 24. Detailed Functional Block Diagram
ONE-TIME
COMPARATOR
DD
is lower than the required V
FUSES
REG.
DAC
EN
of 10 are
MUX
FUSE
REG.
issued as fatal errors
DECODER
DD_OTP
DD_OTP
require-
DD
. The
can be
B
A
W