Initial report by Amit Pitaru, 13, Feb, 2006

Datasheet Report for MAXIM DS1804: Non-Volatile Trimmer Potentiometer


1. Description:

The DS18004 IC operates like a regular potentiometer, but instead of manually rotating a wiper, we can program its position digitally with a micro-controller (or three regular on/off switches). The DS1804 has non-volatile memory, so it remembers the wiper's position when turned off. The DS1804 allows us to move the wiper to 100 different locations (steps), and comes in three models: 10K, 50K, and 100K. Report by Amit Pitaru.




2. Applications

I'm waiting on an order to test this unit, and will update this page accordingly. This is what I think is happening...
The DS1804 can be used instead of a regular POT in any circuit. Being programmable, it is especially suited for auto-calibration applications. For example, it could be used in a voltage-devider circuit, allowing the microchip to determine and save the best resistance-value for the sensor (I'll attempt such a circuit during the semester).




3. Electrical Characteristics

3.1 Download the DS1804 DATASHEET

3.2 Available Models:

Free samples are available on the Maxim site. You may probably want one of these PDIP models (for breadboards/Perf-boards):
DS1804-010 - 10K model
DS1804-050 - 50K model
DS1804-0100 - 100K model

3.3 Voltage Operating Conditions

3.3.a Quick specifications:

- Supplied Voltage, Vcc: The DS1804 requires between 3V and 5V to operate.
- The programmable pins should be provided digital input: 0V (low) / Vcc (high).
- The resistor inputs can take values between Gnd (0) and Vcc (3-5V).

3.3.b Detailed specifications:

Vcc Supply voltage: The DS1804 operates from 2.7V to 5.5V, and can therefor share a power-source with a micro-controller. For optimal operation, supply voltage from 3V to 5V.
Input Logic 1/0: To program the DS1804 (see programming procedure section), supply each of the input pins the following voltages:
To pull the pin down (Low logic-0), supply very low voltage from -0.5V to 0.6V (or maximum of 0.8V if Supplied voltage is very low - 2.7V)
To pull the pin up (High logic-1), supply voltage from 2V to Vcc+0.5V. Vcc is the Supply voltage (usually from 3V to 5V).
Resistor pins: The three resistor pins can handle voltage from Gnd-0.5V to Vcc+0.5V. In a typical circuit Gnd is usually 0V and Vcc is 5V; in this case the pins will handle between -0.5V to 5.5V


4. Pins Description:

* Some of the following text is taken directly from the datasheet:

Power Supply to logic unit and wiper:

VCC - Power Supply. The DS1804 will support supply voltages ranging from +2.7V to +5.5V.
GND - Ground.

Resistor Pins:

H - High-Terminal Potentiometer. This is the high terminal of the potentiometer. It is not required that this terminal be connected to a potential greater than the L-terminal. Voltage applied to the H-terminal cannot exceed the power-supply voltage, VCC, or go below ground.
L - Low-Terminal Potentiometer. This is the low terminal of the potentiometer. It is not required that this terminal be connected to a potential less than the H-terminal. Voltage applied to the L-terminal cannot exceed the power-supply voltage, VCC, or go below ground.
Verify in class: if i get this right - these two pins mirror leads on a regular Pot. In that sense, they are interchangeable (it doesn't matter if L is connected to Vcc and H to Gnd.
W - Wiper of the Potentiometer. This pin is the wiper of the potentiometer. Its position on the resistor array is controlled by the three-terminal control port. Voltage applied to the wiper cannot exceed the power-supply voltage, VCC, or go below ground.

Login-unit pins, used for programming the wiper:

CS - Chip Select. The CS input is used to activate the control port of the DS1804. This input is active low. When in a high-state, activity on the INC and U/ D port pins will not affect or change wiper position.
INC - Wiper Movement Control. This input provides for wiper position changes when the CS pin is low. Wiper position changes of the W-terminal will occur one position per high-to-low transition of this input signal. Position changes will not occur if the CS pin is in a high state.
U/ D - Up/Down Control. This input sets the direction of wiper movement. When in a high state and CS is low, any high-to-low transition on INC will cause a one position movement of the wiper towards the H-terminal. When in a low state and CS is low, any high-to-low transitions on INC will cause the position of the wiper to move towards the L-terminal.

In other words, to program the wiper, do the following:

1. Connect CS to Gnd.
2. To move the wiper towards the H pin, set U/D pin to High (Vcc).
OR To move the wiper towards the L pin, set U/D pin to Low (Gnd).
3. Set INC to High (Vcc), and than Low (Gnd). This transition will move the wiper one unit in the direction set in step 2.