7.3.1 Dual Channel, 256-Position Resolution

The TPL0202 features two independent DPOTs. Each DPOT is capable of being used and controlled independently of the other one.

7.3.2 Non-Volatile Memory

The TPL0202 device features non-volatile memory which is used to store the wiper positions of both potentiometers independently. This allows the user to set the default power-up position of the wiper. By default, this is 0x80h (midscale).

7.4.1 Voltage Divider Mode

The digital potentiometer generates a voltage divider when all three terminals are used. The voltage divider at wiper-to-H and wiper-to-L is proportional to the input voltage at H to L.

Figure 22. Equivalent Circuit for Voltage Divider Mode

For example, connecting terminal H to 5 V and terminal L to ground, the output voltage at terminal W can range from 0 V to 5 V. The general equation defining the output voltage at terminal W for any valid input voltage applied to terminal H and terminal L is:

Equation 1.

The voltage difference between terminal H and terminal W can also be calculated using Equation 2.

Equation 2.

where

• D is the decimal value of the wiper code.

7.4.2 Rheostat Mode

The TPL0202 operates in rheostat mode when only two terminals are used as a variable resistor. The variable resistance can either be between terminal H and terminal W or between terminal L and terminal W.  The unused terminal can be left floating or it can be tied to terminal W. The nominal resistance between terminal H and terminal L is 10 kΩ and has 256 tap points accessed by the wiper terminal. The 8-bit volatile register value is used to determine one of the 256 possible wiper positions.

To set the resistance between terminal H and terminal W in rheostat mode, the potentiometer can be configured in two possible ways.

Figure 23. Equivalent Circuit for Rheostat Mode With Terminal H to Terminal W Resistance

The general equation for determining the digitally-programmed output resistance between terminal H and terminal W is:

Equation 3.

where

• R_TOT is the end-to-end resistance between terminal H and terminal L.
• D is the decimal value of the wiper code.

Similarly, to set the resistance between terminal L and terminal W, the potentiometer can be configured in two possible ways.

Figure 24. Equivalent Circuit for Rheostat Mode With Terminal L to Terminal W Resistance

The general equation for determining the digitally-programmed output resistance between terminal L and terminal W is:

Equation 4.

where

• R_TOT is the end-to-end resistance between terminal H and terminal L.
• D is the decimal value of the wiper code.

7.4.3 Ideal Resistance Values

Figure 25. Digital Potentiometer Measurements

Table 1 shows the ideal values for DPOT with end-to-end resistance of 10 kΩ. The absolute values of resistance can vary significantly, but the ratio (R_WL / R_HW) is extremely accurate.

7.5.1 SPI Digital Interface

The TPL0202 uses a 3-wire SPI-compatible serial data interface. This write-only interface has three inputs: chip-select (CS), data clock (SCLK), and data input (DIN). Drive CS low to enable the serial interface and clock data synchronously into the shift register on each SCLK rising edge. The WRITE commands (C1, C0 = 00 or 01) require 16 clock cycles to clock in the command, address, and data. The COPY commands (C1, C0 = 10 or 11) can use either eight clock cycles to transfer only command and address bits or 16 clock cycles, with the device disregarding 8 data bits. After loading data into the shift register, drive CS high to latch the data into the appropriate potentiometer control register and disable the serial interface. Keep CS low during the entire serial data stream to avoid corruption of the data.

Figure 26. Digital Interface Write Sequence

Figure 27. Digital Interface Timing Diagram

Table 2. Register Map

7.6.1 Digital Interface Format

The data format consists of three elements: command bits, address bits, and data bits. The command bits (C1 and C0) indicate the action to be taken such as changing or storing the wiper position. The address bits (A1 and A0) specify which potentiometer the command affects and the 8 data bits (D7 to D0) specify the wiper position.

7.6.2 Write-Wiper Register (Command 00)

Data written to the write-wiper registers (C1, C0 = 00) controls the wiper positions. The 8 data bits (D7 to D0) indicate the position of the wiper. If DIN = 0x00h, the wiper moves to the position closest to the L terminal. If DIN = 0xFFh, the wiper moves to the position closest to the H terminal. This command writes data to the volatile RAM, leaving the NV registers unchanged. When the device powers up, the data stored in the NV registers transfers to the volatile wiper register, moving the wiper to the stored position

7.6.3 Write-NV Register (Command 01)

This command (C1, C0 = 01) stores the position of the wipers to the NV registers for use at power-up. Alternatively, the copy wiper register to NV register command can be used to store the position of the wipers to the NV registers. Writing to the NV registers does not affect the position of the wipers.

7.6.4 Copy Wiper Register to NV Register (Command 10)

This command (C1, C0 = 10) stores the current position of the wiper to the NV register, for use at power-up. This command may affect one potentiometer at a time, or both simultaneously, depending on the state of A1 and A0. Alternatively, the write NV register command can be used to store the current position of the wiper to the NV register.

7.6.5 Copy NV Register to Wiper Register (Command 11)

This command (C1, C0 = 11) restores the wiper position to the previously stored position in the NV register. This command may affect one potentiometer at a time, or both simultaneously, depending on the state of A1 and A0.