DS1668

The DS1668 and DS1669 Dallastats are digital rheostats or potentiometers. These units provide 64 possible uniform tap points over the resistive range and are available in standard versions of 10K, 50K, and 100K ohms. The Dallastats can be controlled by either a mechanicaltype contact closure input or a digital source input such as a CPU. Wiper position is maintained in the absence of power which is accomplished through the use of a EEPROM memory cell array. The EEPROM cell array is specified to accept greater than 80,000 writes.

The DS1668 and DS1669 differ in the type packages in which they are offered. The DS1668 is only available in a custom 6pin package with a single integrated pushbutton as shown in the package drawing. The single integrated pushbutton provides the mechanical control input of the wiper position. In addition, a digital source input, D, allows the potentiometer to be controlled by a microcontroller or processor. Other package pins include the positive voltage input, +V, the negative voltage input, V, the resistor wiper terminal, RW, and the high resistor terminal, RH. The DS1668 is rated for commercial temperature usage only (0 to 70).

The DS1669 is offered in two standard IC packages which include an 8pin 300 mil DIP and an 8pin 200 mil SOIC. Like the DS1668, the DS1669 can be configured to operate using a single pushbutton or digital source input. This is illustrated in Figure 1. Additionally, the DS1669 can be configured to operate in a dual pushbutton configuration which is shown in Figure 2. The DS1669 pinouts allow access to both ends of the potentiometer RL, RH, and the wiper, RW. Control inputs include the digital source input, D, the up contact input, UC, and the down contact input, DC. Other package pinouts include the positive,+V, and negative, V , supply inputs. The DS1669 is available in commercial or industrial temperature versions.

The DS1668/DS1669 Dallastats are controlled through a contact closure input or by a digital source input. The DS1668 is configured to operate from a single contact closure (pushbutton) input which is integrated in the custom 6pin package or the device can be driven from the digital source input (D). The DS1669 can be controlled using a single pushbutton input, dual pushbutton, or using the digital source input.

Figure 3 illustrates the single pushbutton configuration of the DS1668. Internally, the low end resistor terminal is connected to the negative supply input terminal. The integrated pushbutton has one side connected to the negative supply input while the other side is connected to the up contact terminal (UC). The digital source input (D) is accessible through pin 4 of the package. The (D) input has an internal pullup resistor and can be allowed to float when not in use. The down contact input (DC) is not accessible externally. However, this control input is internally connected to the positive input supply.

When powered, the DS1668 assumes a single pushbutton mode of operation. Pressure applied to the integrated pushbutton will cause contact closure which in turn will move the wiper position upward or downward depending on the previous wiper direction. Single pushbutton mode is accomplished in the same manner for the DS1669. However, for the DS1669, all connections must be made by the user since no internal connections exist (see Figure 1). Note that single pushbutton control is accomplished when 1) the (DC) input is connected to the positive supply input and 2) the (D) input is allowed to float. These two conditions must exist from the time of device powerup. The UC input controls both upward and downward movement of the device wiper position in single pushbutton mode of operation.

Dual pushbutton operation is only available when using the DS1669. The DS1668, by design, only supports the single pushbutton mode of operation and digital source input control. Figure 2 provides a typical application example of the dual pushbutton configuration for the DS1669. In dualpushbutton mode, the upcontact input (UC) is used solely to provide upward movement of the wiper position and the downcontact input (DC) is used to provide downward movement of the wiper position.

For dual pushbutton configuration, DS1668 and DS1669 all control inputs (UC, DC, and D) must remain open on device powerup.

The DS1668 and DS1669 digital source input, D, was designed for microprocessor or controller 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.