DS3903 Maxim Integrated Products, DS3903 Datasheet - Page 11

• Manufacturer Part Number: DS3903
• Description: DS3903 Triple 128-Position Nonvolatile Digital Potentiometer
• Manufacturer: Maxim Integrated Products

the appropriate device address bit, and the read/write
bit, the slave device outputs an acknowledge signal on
the SDA line.
To achieve the best results when using the DS3903,
decouple the power supply with a 0.01µF or 0.1µF
capacitor. Use a high-quality ceramic surface-mount
capacitor if possible. Surface-mount components mini-
mize lead inductance, which improves performance,
and ceramic capacitors tend to have adequate high-
frequency response for decoupling applications.
The write-protect pin has an internal pullup resistor. To
be able to adjust the potentiometers’ position, this pin
must be grounded. This pin can be left floating or con-
nected to V
tions.
Two substantial differences between digital poten-
tiometers and mechanical potentiometers are the wiper
resistance and the wiper current limit. The wiper resis-
tance (R
on the IC between the internal resistive elements and
the wiper pin. This can be modelled by using an ideal
potentiometer, with a resistance of R
between the ideal wiper and wiper terminal of the digi-
tal potentiometer. One final note about the wiper resis-
tance is that it has a high temperature coefficient
(approximately +3000PPM), which can be noticeable in
certain circuit configurations.
The wiper current limit (I
necting materials between the internal resistive ele-
ments and the wiper terminal. While it may be possible
to exceed this value for a short period without prob-
lems, exceeding the wiper current limit is a long-term
reliability problem.
Both characteristics can be minimized in designs by
connecting the wiper terminal to high-impedance
loads. This reduces both the current through the wiper
and the voltage drop across the wiper resistance.
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
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© 2002 Maxim Integrated Products
Wiper Resistance and Wiper Current Limit
W
) is a result of the interconnecting materials
CC
Applications Information
to write protect the potentiometer posi-
Power-Supply Decoupling
W
) is also due to the intercon-
Write Protection
Printed USA
W
Triple 128-Position Nonvolatile
connected
There are two ways to make a digital potentiometer into
a variable resistor. The first is to short the wiper terminal
to the high- or low-side terminal. This places wiper
resistance in parallel with the resistance from the wiper
to the high or low side of the potentiometer. The advan-
tage of this method is that it reduces the current
through the wiper, which is advantageous if the current
is approaching the wiper current limit. The disadvan-
tage is that the wiper resistance makes the resistance
versus position nonlinear, particularly for low-resistance
values.
The second way is to attach the wiper terminal, and
either the low- or high-side terminal. The unattached
terminal is connected to the wiper by the resistance
internal to the part, and stays at the same voltage as
the wiper. This method provides a linear resistance ver-
sus position function, but it limits the current through
the resistance to I
ing between the wiper resistance and the paralleled
resistive elements.
Both configurations are heavily influenced by the wiper
resistance, particularly over temperature, where its tem-
perature coefficient noticeably affects the resistor’s value.
For the latest package outline information, go to www.maxim-ic.
com/packages.
TRANSISTOR COUNT: 10,793
SUBSTRATE CONNECTED TO GROUND
Digital Potentiometer
is a registered trademark of Maxim Integrated Products.
W
Using a Potentiometer as a
since there is no current load shar-
Package Information
Chip Information
Variable Resistor