DS1669
Dallastat Electronic Digital Rheostat
www.maxim-ic.com
FEATURES
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Replaces mechanical variable resistors
Electronic interface provided for digital as
well as manual control
Wide differential input voltage range
between 4.5 and 8V
Wiper position is maintained in the absence
of power
Low-cost alternative to mechanical controls
Applications include volume, tone, contrast,
brightness, and dimmer control
Available in 8-pin SOIC and 8-pin DIP
packages
Standard resistance values for Dallastat:
-
DS1669-10 ~ 10 kΩ
-
DS1669-50 ~ 50 kΩ
-
DS1669-100 ~ 100 kΩ
Operating Temperature Range
-
Industrial: -40°C to +85°C
PIN ASSIGNMENT DS1669
(R
H
)
UC
D
(R
L
)
1
2
3
4
8
7
6
5
+V
DC
R
W
V-
8-Pin SOIC (208-mil)
See Mech. Drawings Section
(R
H
)
UC
D
(R
L
)
1
2
3
4
8
7
6
5
+V
DC
R
W
-V
§
8-Pin DIP (300-mil)
See Mech. Drawings Section
PIN DESCRIPTION DS1669
R
H
R
W
R
L
-V, +V
UC
D
DC
- High Terminal of Potentiometer
- Wiper Terminal of Potentiometer
- Low Terminal of Potentiometer
- Voltage Inputs
- Up Contact Input
- Digital Input
- Down Contact Input
DESCRIPTION
The DS1669 Dallastat is a digital rheostat or potentiometer. This device provides 64 possible uniform tap
points over the entire resistive range. The standard resistive ranges are 10 kW, 50 kW, and 100 kW. The
Dallastat can be controlled by either a switch contact closure input or a digital source input such as a
CPU. Wiper position is maintained in the absence of power through the use of a EEPROM memory cell
array. The EEPROM cell array will withstand more than 50,000 writes.
The DS1669 is offered in two standard IC packages which include an 8-pin 300-mil DIP and an 8-pin
208-mil SOIC. The DS1669 can be configured to operate using a single pushbutton, dual pushbutton or
digital source input by varying power-on conditions. This is illustrated in Figures 1 and 2. The DS1669
pinouts allow access to both ends of the potentiometer R
L
, R
H
, and the wiper, R
W
. Control inputs include
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DS1669
the digital source input, D, the up contact input, UC, and the down contact input, DC. Other pins include
the positive, +V, and negative, -V, supply inputs. The DS1669 is specified to operate from -40°C to
+85°C.
OPERATION
The DS1669 can be configured to operate from a single contact closure, dual contact closure, or a digital
source input. Figures 1 and 2 illustrate both contact closure configurations. Contact closure is defined as a
transition from a high level to a low level on the up contact (UC) or down contact (DC) inputs. All three
control inputs are active when in a low state and are inactive when in a high state.
The DS1669 interprets input pulse widths as the means of controlling wiper movement. A single pulse
input on the UC, DC, or D input terminals will cause the wiper position to move 1/64
th
of the total
resistance. A transition from a high to low on these inputs is considered the beginning of pulse activity or
contact closure. A single pulse must be greater than 1 ms but lasting no longer than 1 second. Pulse
timings are shown in Figure 5.
Repetitive pulsed inputs can be used to step through each resistive position of the device in a relatively
fast manner (see Figure 5b). The requirement for repetitive pulsed inputs is that pulses must be separated
by a minimum time of 1 ms. If the input is not allowed to be inactive (high) for at least 1 ms, the DS1669
will interpret repetitive pulses as a single pulse.
Pulse inputs lasting longer than 1 second will cause the wiper to move one position every 100 ms
following the initial 1-second hold time. The total time to transcend the entire potentiometer using a
continuous input pulse is given by the formula below:
»1
second + 63 X 100 ms = 7.3 (seconds)
Single contact closure operation allows the user to control wiper movement in either direction from a
single pushbutton input. Figure 1 presents a typical single pushbutton configuration. The UC input is used
to increment and decrement wiper position for single pushbutton mode of operation. The DC input
provides no functionality in this mode but must be connected to the positive supply voltage (V
CC
). The
digital source input (D) can be allowed to float.
On device power-up, the configuration shown in Figure 1 must exist in order to enter the single contact
closure mode of operation¾especially and specifically, the (DC) input’s direct connection to the positive
supply voltage (V
CC
).
The initial direction of wiper movement in single pushbutton operation is determined by prior activity.
The initial direction of wiper movement will be opposite to that of the previous activity. Changing the
direction of wiper movement in single pushbutton mode is accomplished by allowing a period of
inactivity on the UC input of (greater than) 1 second, or by moving the wiper to the end of the
potentiometer range. This will occur regardless of whether the input is a continuous pulse, a sequence of
repetitive pulses or a single pulse.
The digital source input, D, was designed for microprocessor or controlled applications. This control
input manipulates the device in the same manner as the single pushbutton configuration, controlling
movement of the wiper position in both upward and downward directions. One added feature over the
single pushbutton configuration is the ability to increment or decrement wiper position at a faster rate.
Digital source input control is available regardless of the type of pushbutton configuration.
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Dual pushbutton mode of operation is entered when the DC input is floated on power-up. If interfacing
contact closure control inputs to digital logic, the DC input must be interfaced to an open drain drive
which is high impedance during power-up; see Figure 2B. This will prevent the device from entering a
single pushbutton mode of operation.
In dual pushbutton mode, each direction is controlled by the up contact (UC) and down contact (DC)
inputs, respectively. No wait states are required to change wiper direction in dual pushbutton mode. In
dual pushbutton mode, as the wiper position reaches the end of the potentiometer, the direction of wiper
movement will not change. Wiper position will remain at the potentiometers’ end until an opposite
direction input is given.
All contact closure control inputs, UC, DC, and D, are internally pulled-up by a 100 kW resistance. The
UC and DC inputs are internally debounced and require no external components for input signal
conditioning.
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DS1669
DS1669 SINGLE PUSHBUTTON CONFIGURATION (TYPICAL EXAMPLE)
Figure 1
DS1669 DUAL PUSHBUTTON CONFIGURATION (TYPICAL APPLICATION)
Figure 2A
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DS1669
DS1669 DUAL PUSHBUTTON CONFIGURATION (TYPICAL APPLICATION)
Figure 2B
The DS1669 is provided with two supply inputs -V and +V. The maximum voltage difference between
the two supply inputs is +8.0 volts. The minimum voltage difference is +4.5 volts. All input levels are
referenced to the negative supply input, -V. The voltage applied to any Dallastat terminal must not exceed
the negative supply voltage (-V ) by -0.5 or the positive supply voltage (+V) by +0.5 volts. The minimum
logic high level must be +2.4 volts with reference to the -V supply voltage input for +V=5V. A logic low
level with reference to the -V supply voltage has a maximum value of +0.8 volts. Dallastats exhibit a
typical wiper resistance of 400 ohms with a maximum wiper resistance of 1000 ohms. The maximum
wiper current allowed through the Dallastat is specified at 1 milliamps (see DC Electrical
Characteristics).
NONVOLATILE WIPER SETTINGS
Dallastats maintain the position of the wiper in the absence of power. This feature is provided through the
use of EEPROM type memory cell arrays. During normal operation the position of the wiper is
determined by the input multiplexer. Periodically, the multiplexer will update the EEPROM memory
cells. The manner in which an update occurs has been optimized for reliability, durability, and
performance. Additionally, the update operation is totally transparent to the user.
When power is applied to the Dallastat, the wiper setting will be the last recorded in the EEPROM
memory cells. If the Dallastat setting is changed after power is applied, the new value will be stored after
a delay of 2 seconds. The initial storage of a new value after power-up occurs when the first change is
made, regardless of when this change is made.
After the initial change on power-up, subsequent changes in the Dallastat EEPROM memory cells will
occur only if the wiper position of the part is moved greater than 12.5% of the total resistance range. Any
wiper movement after initial power-up which is less than 12.5% will not be recorded in the EEPROM
memory cells. Since the Dallastat contains a 64-to-1 multiplexer, a change of greater than 12.5%
corresponds to a change of the fourth LSB.
Changes or storage to the EEPROM memory cells must allow for a 2-second delay to guarantee that
updates will occur. The EEPROM memory cells are specified to accept greater than 80,000 writes before
a wear-out condition. If the EEPROM memory cells do reach a wear-out condition, the Dallastat will still
function properly while power is applied. However, on power-up the device’s wiper position will be that
of the position last recorded before memory cell wear-out.
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