AD5170 Analog Devices, AD5170 Datasheet - Page 12

• Manufacturer Part Number: AD5170
• Description: 256-Position Two-Time Programmable I2C Digital Potentiometer
• Manufacturer: Analog Devices

AD5170
OPERATION
The AD5170 is a 256-position, digitally controlled variable
resistor (VR) that employs fuse link technology to achieve
memory retention of resistance setting.
An internal power-on preset places the wiper at midscale
during power-on. If the OTP function has been activated, the
device powers up at the user-defined permanent setting.
ONE-TIME PROGRAMMING (OTP)
Prior to OTP activation, the AD5170 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 5 and Table 6).
Note that fuse link technology requires 6 V to blow the internal
fuses to achieve a given setting. The user is allowed only one
attempt at blowing the fuses. Once programming is completed,
the power supply voltage must be reduced to the normal
operating range of 2.7 V to 5.5 V.
The device control circuit has two validation bits, E1 and E0,
that can be read back to check the programming status (see
Table 7). 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. Figure 30 shows a detailed functional block diagram.
PROGRAMMING THE VARIABLE RESISTOR AND
VOLTAGE
Rheostat Operation
The nominal resistance of the RDAC between terminals A and
B is available in 2.5 kΩ, 10 kΩ, 50 kΩ, and 100 kΩ. The nominal
resistance (R
the wiper terminal, plus the B terminal contact. The 8-bit data
in the RDAC latch is decoded to select one of the 256 possible
settings.
AB
) of the VR has 256 contact points accessed by
SDA
SCL
CONTROL BLOCK
PROGRAM/TEST
I
2
C INTERFACE
ONE-TIME
COMPARATOR
Figure 30. Detailed Functional Block Diagram
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FUSES
REG.
DAC
EN
Assuming a 10 kΩ part is used, the wiper’s first connection
starts at the B terminal for data 0x00. Because there is a 50 Ω
wiper contact resistance, such a connection yields a minimum
of 100 Ω (2 × 50 Ω) resistance between terminals W and B. The
second connection is the first tap point, which corresponds to
139 Ω (R
0x01. The third connection is the next tap point, representing
178 Ω (2 × 39 Ω + 2 × 50 Ω) for data 0x02, and so on. Each LSB
data value increase moves the wiper up the resistor ladder until
the last tap point is reached at 10,100 Ω (R
MUX
FUSE
REG.
A
B
WB
= R
Figure 32. AD5170 Equivalent RDAC Circuit
DECODER
W
Figure 31. Rheostat Mode Configuration
SD BIT
AB
D7
D6
D5
D4
D3
D2
D1
D0
DECODER
LATCH
/256+ 2 × R
RDAC
AND
A
B
R
R
R
R
W
S
S
S
S
= 39 Ω + 2 × 50 Ω) for data
W
A
W
B
AB
A
B
+ 2 × R
A
W
B
W
W
).