AD5161BRMZ100 Analog Devices Inc, AD5161BRMZ100 Datasheet - Page 15

• Manufacturer Part Number: AD5161BRMZ100
• Description: IC DGTL POT SPI 100K 10-MSOP
• Manufacturer: Analog Devices Inc

Specifications of AD5161BRMZ100

• Temperature Coefficient: 45 ppm/°C Typical
• Taps: 256
• Resistance (ohms): 100K
• Number Of Circuits: 1
• Memory Type: Volatile
• Interface: I²C, SPI
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Resistance In Ohms: 100K
• End To End Resistance: 100kohm
• No. Of Steps: 256
• Resistance Tolerance: ± 30%
• Supply Voltage Range: 2.7V To 5.5V
• Control Interface: Serial, I2C
• No. Of Pots: Single
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

THEORY OF OPERATION
The AD5161 is a 256-position digitally controlled variable
resistor (VR)
An internal power-on preset places the wiper at midscale during
power-on, which simplifies the fault condition recovery at power-up.
PROGRAMMING THE VARIABLE RESISTOR
Rheostat Operation
The nominal resistance of the RDAC between terminals A and
B is available in 5 kΩ, 10 kΩ, 50 kΩ, and 100 kΩ. The final two
or three digits of the part number determine the nominal resistance
value, e.g., 10 kΩ = 10; 50 kΩ = 50. The nominal resistance (R
the VR has 256 contact points accessed by 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. Assume a 10 kΩ
part is used, the wiper’s first connection starts at the B terminal
for data 0x00. Since there is a 60 Ω wiper contact resistance, such
connection yields a minimum of 60 Ω resistance between
Terminals W and B. The second connection is the first tap point,
which corresponds to 99 Ω (R
for data 0x01. The third connection is the next tap point,
representing 177 Ω (2 × 39 Ω + 60 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 9961 Ω (R
Figure 42 shows a simplified diagram of the equivalent RDAC
circuit where the last resistor string will not be accessed;
therefore, there is 1 LSB less of the nominal resistance at full
scale in addition to the wiper resistance.
1
The terms digital potentiometer, VR, and RDAC are used interchangeably.
1
Figure 42. AD5161 Equivalent RDAC Circuit
device.
SD BIT
D7
D6
D5
D4
D3
D2
D1
D0
DECODER
LATCH
RDAC
AND
R
R
R
R
WB
S
S
S
S
= R
AB
/256 + R
AB
– 1 LSB + R
W
W
A
B
= 39 Ω + 60 Ω)
W
).
AB
Rev. A | Page 15 of 20
) of
The general equation determining the digitally programmed
output resistance between W and B is
where D is the decimal equivalent of the binary code loaded in
the 8-bit RDAC register, R
R
the internal switch.
In summary, if R
the following output resistance R
RDAC latch codes.
Table 9. Codes and Corresponding R
D (Dec.)
255
128
1
0
Note that in the zero-scale condition a finite wiper resistance of
60 Ω is present. Care should be taken to limit the current flow
between W and B in this state to a maximum pulse current of
no more than 20 mA. Otherwise, degradation or possible
destruction of the internal switch contact can occur.
Similar to the mechanical potentiometer, the resistance of the
RDAC between the wiper W and terminal A also produces a
digitally controlled complementary resistance R
terminals are used, the B terminal can be opened. Setting the
resistance value for R
and decreases as the data loaded in the latch increases in value.
The general equation for this operation is
For R
following output resistance R
RDAC latch codes.
Table 10. Codes and Corresponding R
D (Dec.)
255
128
1
0
Typical device to device matching is process lot dependent and
may vary by up to ±30%. Since the resistance element is processed
in thin film technology, the change in R
a very low 45 ppm/°C temperature coefficient.
W
is the wiper resistance contributed by the on resistance of
R
R
AB
WB
WA
= 10 kΩ and the B terminal open circuited, the
(
(
D
D
R
9,961
5,060
99
60
)
)
WB
=
=
AB
(Ω)
256
256
D
R
99
5,060
9,961
10,060
= 10 kΩ and the A terminal is open circuited,
256
WA
×
−
WA
(Ω)
R
D
Output State
Full Scale (R
Midscale
1 LSB
Zero Scale (Wiper Contact Resistance)
AB
starts at a maximum value of resistance
×
AB
R
+
AB
is the end-to-end resistance, and
R
WA
W
+
will be set for the indicated
WB
R
AB
W
will be set for the indicated
Output State
Full Scale
Midscale
1 LSB
Zero Scale
– 1 LSB + R
WB
AB
WA
Resistance
with temperature has
Resistance
W
WA
)
. When these
AD5161
(1)
(2)