AD5245BRJZ5-R2 Analog Devices Inc, AD5245BRJZ5-R2 Datasheet - Page 13

• Manufacturer Part Number: AD5245BRJZ5-R2
• Description: IC DGTL POT 256POS SOT-23-8 T/R
• Manufacturer: Analog Devices Inc

Specifications of AD5245BRJZ5-R2

• Taps: 256
• Resistance (ohms): 5K
• Number Of Circuits: 1
• Temperature Coefficient: 45 ppm/°C Typical
• Memory Type: Volatile
• Interface: I²C, 2-Wire Serial
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-8
• Resistance In Ohms: 5K
• End To End Resistance: 5kohm
• No. Of Steps: 256
• Resistance Tolerance: ± 30%
• Supply Voltage Range: 2.7V To 5.5V
• Control Interface: I2C, Serial
• No. Of Pots: Single
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AD5245EVAL - BOARD EVAL FOR AD5245
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: AD5245BRJZ5-R2; AD5245BRJZ5-R2TR

THEORY OF OPERATION
The AD5245 is a 256-position digitally controlled variable
resistor (VR) device.
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 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.
Assuming that 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
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
A
B
WB
= R
AB
Figure 36. AD5245 Equivalent RDAC Circuit
) of the VR has 256 contact points accessed by
AB
W
Figure 35. Rheostat Mode Configuration
D7
D6
D5
D4
D3
D2
D1
D0
DECODER
/256 + 2 × R
LATCH
RDAC
AND
A
B
R
R
R
R
W
S
S
S
S
= 39 Ω + 2 × 50 Ω) for Data 0x01.
W
AB
+ 2 × R
A
B
A
W
B
W
W
).
Rev. B | Page 13 of 20
The general equation determining the digitally programmed
output resistance between W and B is
where:
8-bit RDAC register.
the internal switch.
In summary, if R
circuited, then the following output resistance R
indicated RDAC latch codes.
Table 6. Codes and Corresponding R
D (Dec.)
255
128
1
0
Note that in the zero-scale condition, a finite wiper resistance of
100 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
latch codes.
Table 7. Codes and Corresponding R
D (Dec.)
255
128
1
0
Typical device-to-device matching is process lot dependent and
can vary by up to ±30%. Because the resistance element is
processed in thin film technology, the change in R
temperature has a very low 45 ppm/°C temperature coefficient.
is the decimal equivalent of the binary code loaded in the
is the wiper resistance contributed by the on resistance of
is the end-to-end resistance.
AB
= 10 kΩ and the B terminal open circuited, the
(
(
)
R
9,961
5,060
139
100
)
=
WB
=
256
256
(Ω)
AB
256
R
139
5,060
9,961
10,060
= 10 kΩ and the A terminal is open
WA
−
×
WA
(Ω)
Output State
Full Scale (R
Midscale
1 LSB
Zero Scale (Wiper Contact Resistance)
starts at a maximum value of resistance
×
+
2
WA
×
+
2
is set for the indicated RDAC
×
AB
Output State
Full Scale
Midscale
1 LSB
Zero Scale
– 1 LSB + R
WB
WA
Resistance
Resistance
W
WB
WA
)
AB
. When these
is set for the
AD5245
with
(1)
(2)