AD5235BRU25-RL7 Analog Devices Inc, AD5235BRU25-RL7 Datasheet - Page 26

• Manufacturer Part Number: AD5235BRU25-RL7
• Description: IC DGTL POT DUAL 1024POS 16TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD5235BRU25-RL7

• Rohs Status: RoHS non-compliant
• Taps: 1024
• Resistance (ohms): 25K
• Number Of Circuits: 2
• Temperature Coefficient: 35 ppm/°C Typical
• Memory Type: Non-Volatile
• Interface: 4-Wire SPI Serial
• Voltage - Supply: 3 V ~ 5.5 V, ±2.25 V ~ 2.75 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP (0.173", 4.40mm Width)
• Number Of Elements: 2
• # Of Taps: 1024
• Resistance (max): 25KOhm
• Power Supply Requirement: Single/Dual
• Interface Type: Serial (4-Wire/SPI)
• Single Supply Voltage (typ): 3.3/5V
• Dual Supply Voltage (typ): ±2.5V
• Single Supply Voltage (min): 3V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (min): ±2.25V
• Dual Supply Voltage (max): ±2.75V
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 16
• Lead Free Status / RoHS Status: Not Compliant
• Other names: AD5235BRU25-RL7; AD5235BRU25-RL7TR

AD5235
RESISTANCE SCALING
The AD5235 offers 25 kΩ or 250 kΩ nominal resistance. When
users need lower resistance but must maintain the number of
adjustment steps, they can parallel multiple devices. For example,
Figure 57 shows a simple scheme of paralleling two channels of
RDACs. To adjust half the resistance linearly per step, program
both RDACs concurrently with the same settings.
In voltage divider mode, by paralleling a discrete resistor, as
shown in Figure 58, a proportionately lower voltage appears at
Terminal A to Terminal B. This translates into a finer degree of
precision because the step size at Terminal W is smaller. The
voltage can be found as
Figure 57 and Figure 58 show that the digital potentiometers
change steps linearly. Alternatively, pseudo log taper adjustment
is usually preferred in applications such as audio control. Figure 59
shows another type of resistance scaling. In this configuration,
the smaller the R2 with respect to R
taper characteristic of the circuit behaves.
The equation is approximated as
Users should also be aware of the need for tolerance matching
as well as for temperature coefficient matching of the components.
Figure 57. Reduce Resistance by Half with Linear Adjustment Characteristics
Figure 59. Resistor Scaling with Pseudo Log Adjustment Characteristics
V
R
W
E
QUIVALENT
(
D
)
=
Figure 58. Lowering the Nominal Resistance
R3
(
R
=
+
AB
D
R
//
AB
×
A1
B1
R2
R
//
R2
D
AB
A1
B1
R2
)
×
W1
+
×
R
R3
R1
51
A
B
AB
1024
W1
,
D
V
200
A2
B2
0
+
DD
W
R
51
AB
×
+
,
, the more the pseudo log
W2
V
200
1024
DD
×
R
(16)
(17)
Rev. C | Page 26 of 28
RESISTANCE TOLERANCE, DRIFT, AND
TEMPERATURE COEFFICIENT MISMATCH
CONSIDERATIONS
In rheostat mode operation, such as gain control, the tolerance
mismatch between the digital potentiometer and the discrete
resistor can cause repeatability issues among various systems
(see Figure 60). Because of the inherent matching of the silicon
process, it is practical to apply the dual-channel device in this
type of application. As such, R1 can be replaced by one of the
channels of the digital potentiometer and programmed to a
specific value. R2 can be used for the adjustable gain. Although it
adds cost, this approach minimizes the tolerance and temperature
coefficient mismatch between R1 and R2. This approach also
tracks the resistance drift over time. As a result, these less than
ideal parameters become less sensitive to system variations.
Note that the circuit in Figure 61 can track tolerance, temperature
coefficient, and drift in this particular application. The characteristic
of the transfer function is, however, a pseudo log rather than a
linear gain function.
Figure 61. Nonlinear Gain Control with Tracking Resistance Tolerance and Drift
Figure 60. Linear Gain Control with Tracking Resistance Tolerance,
Drift, and Temperature Coefficient
* REPLACED WITH ANOTHER
CHANNEL OF RDAC
R1*
A
V
i
R
V
W
i
B
AD8601
–
+
–
AD8601
+
C1
B
W
U1
R2
C1
U1
A
V
O
V
O