DS1809
Dallastat
www.dalsemi.com
FEATURES
64-position linear taper
Two nonvolatile wiper storage options
Operates from +4.5 to +5.5-volt supplies
Operating Temperature Range:
- Industrial: -40°C to +85°C
Electronic interface provides either digital or
pushbutton control
Low-cost alternative to mechanical solutions
Standard Resistance Values
- DS1809-010
10 kΩ
- DS1809-050
50 kΩ
- DS1809-100
100 kΩ
PIN ASSIGNMENT
R
H
UC
STR
R
L
1
2
3
4
8
7
6
5
V
CC
DC
R
W
GND
8-Pin DIP
8-Pin SOIC (150-mil)
8-Pin µSOP (118-mil)
PIN DESCIPTION
V
CC
R
H
R
L
R
W
UC
DC
STR
GND
-
-
-
-
-
-
-
-
Supply Voltage
High End of Resistor
Low End of Resistor
Wiper Terminal
Up Control Input
Down Control Input
Storage Enable Input
Ground
DESCRIPTION
The DS1809 Dallastat is a nonvolatile digitally controlled potentiometer that provides 64 uniform wiper
positions over the entire resistor range; including the high-end and low-end terminals of the device. The
DS1809 is a low power device capable of operating from power supplies of +4.5V to +5.5V. The device
is ideal for low-power, portable, or battery powered applications.
Wiper position is maintained in the absence of power. This is accomplished via the use of an EEPROM
cell array. The device provides for two storage methods, which include an auto-store capability and a
command-initiated storage function. The EEPROM cell array is specified to accept greater than 50k
writes. Storage of the wiper position is discussed in the Wiper Storage section of this datasheet.
Wiper positioning is controlled via a patented dual pushbutton (or contact closure) interface. For simple
pushbutton-controlled applications or CPU-generated control signals, external debounce circuitry is not
needed. The control interface will support both repetitive pulse inputs and continuous pulse (“push-and-
hold”) inputs. Repetitive pulse and continuous pulse control as well as timing diagrams are discussed in
the section entitled “OPERATION.”
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DS1809
The DS1809 is available in standard 10 kΩ, 50 kΩ, and 100 kΩ=resistor versions. The DS1809 is
provided as an industrial temperature grade part only. Available packaging for the DS1809 include an 8-
lead (300-mil) DIP an 8-lead (150-mil) SOIC, and an 8-lead (118-mil)
µSOP.
BLOCK DIAGRAM
Figure 1
OPERATION
The DS1809 Dallastat is a digitally controlled, nonvolatile potentiometer. A block diagram of the
DS1809 is shown in Figure 1. The DS1809 is a linear potentiometer providing 64-uniform wiper
positions over the entire resistor range including the end-terminals. All three potentiometer terminals of
the device are accessible. These terminals include R
H
, R
L
, and R
W
. R
H
and R
L
are the end-terminals of the
potentiometer. These terminals will have a constant resistance between them as defined by the
potentiometer value chosen: 10 kΩ, 50 kΩ, or the 100 kΩ=version. Functionally, R
H
and R
L
are
interchangeable. The wiper terminal, R
W
, is the multiplexed terminal and can be set to one of the 64 total
positions that exist on the resistor ladder including the R
H
and R
L
terminals.
Control of the wiper (R
W
) position setting is accomplished via the two inputs UC and DC. The UC and
DC control inputs, when active, determine the direction on the resistor array that the wiper position will
move. The UC (up control) control input is used to move the wiper position towards the R
H
terminal. The
DC (down control) control input is used to move wiper position towards the R
L
terminal.
The control inputs UC and DC are active low inputs that interpret input pulse widths as the means of
controlling wiper movement. Internally, these inputs are pulled up to V
CC
via a 100 kΩ=resistance. A
transition from a high-to-low on these inputs is considered the beginning of pulse input activity.
A single pulse on the UC or DC input is defined as being greater than 1 millisecond but lasting no longer
that ½ second. This type pulse input will cause the wiper position of the Dallastat to move one position.
Multiple pulse inputs (repetitive pulse inputs) can be used to step through each wiper position of the
device. The requirement for a repetitive pulse train on the UC or DC inputs is that pulses must be
separated by a minimum high time of 1 millisecond. If this is not the case the Dallastat will ignore that
pulse input.
A continuous pulse input (“push and hold”) is defined as lasting longer that ½ second. A continuous pulse
input will cause the wiper position to move one position every 100 milliseconds following the initial ½-
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DS1809
second hold time. The total time to transcend the entire potentiometer given a continuous pulse input is
provided by the equation:
½(second) + 62 X 100 ms = 6.7 (seconds)
If the wiper position of the DS1809 is incremented to an end-position, it will stay at that position until the
device receives an opposite direction input pulse command over the UC or DC inputs. For example, if the
wiper position is incremented to the R
H
terminal using the UC input control, it will stay at that position
until UC is first deactivated, and then the DC input is activated to move the wiper position towards the R
L
terminal.
The UC and DC control inputs are designed to support simple pushbutton inputs or CPU generated
inputs. Figure 2 illustrates the requirements for pushbutton generated controls. For manual pushbutton
controls all that is required are the desired pushbuttons to implement contact closure. No external
debounce or timing circuitry is needed to support the pushbutton operation.
Applications using CPU generated controls must power the UC and DC control pins in a high state to
avoid any inadvertent wiper position movement. To help prevent inadvertent wiper position movement
during a power-up, the DS1809 locks out the control port inputs for a minimum time of 10 ms.
WIPER STORAGE
As stated earlier, the DS1809 provides for two methods of nonvolatile wiper storage using internal
EEPROM memory cells. These two methods include an autostore configuration and a command initiated
storage operation, both of which utilize the STR input pin. The EEPROM cell array of the DS1809 is
designed to accept greater than 50k writes.
AUTOSTORAGE
The autostore configuration is designed to provide wiper position storage as the part powers down;
writing the current wiper position into memory. The configuration for initiating the automatic storage
capability of the DS1809 is shown in Figure 3. As shown in this configuration, two external devices are
required to insure proper wiper storage. This includes a Schottky diode and a 10-uf capacitor. The
automatic store configuration will cause the DS1809 to initiate storage of wiper position when power
(V
CC
) to the device is removed. The 10-uF capacitor and Schottky diode are used to provide supplemental
power for wiper storage.
COMMAND-INITIATED WIPER STORAGE
The DS1809 will also support a command-initiated wiper storage operation during powered conditions.
For command initiated storage the STR pin should be held in a low state on power-up; otherwise the part
will assume an autostore configuration. As shown in Figure 5, a low-to-high pulse lasting at least 1
µs
on
the STR input will cause the DS1809 to initiate the storage of the current wiper position into EEPROM
when V
CC
is present.
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DS1809
PUSHBUTTON CONFIGURATION
Figure 2
It is assumed that the STR input will be controlled by either external logic or CPU driven. No external
capacitors or diodes are needed for the command-initiated storage operation.
The STR input will take precedence over the pushbutton inputs UC and DC.
AUTOSTORE CONFIGURATION
Figure 3
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DS1809
PUSHBUTTON TIMING DIAGRAMS
Figure 4
If during any pushbutton activity the STR input is activated, pushbutton operation will be suspended until
the storage of EEPROM has been completed. Once complete, pushbutton inputs, if still active, will
resume from the point of suspension. Command initiated storage operations will require a minimum of
4 ms to complete the storage operation. This 4 ms is measured from the rise of STR input (see Figure 5).
For applications not requiring or using the nonvolatile memory feature of the DS1809, it is recommended
that the STR input be connected to GND.
COMMAND INITIATED WIPER STORAGE
- Figure 5
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