SNAA348 April   2021 TPL1401

 

  1.   Design Objective
  2.   Design Description
  3.   Design Notes
  4.   Design Simulations
    1.     Transient Simulation Results
  5.   Register Settings
  6.   Pseudo Code Example
  7.   Design Featured Devices
  8.   Design References

Design Notes

  1. The TPL1401 256-Tap, High-Accuracy, Digital Potentiometer With Buffered Wiper Data Sheet recommends using a 100-nF decoupling capacitor for the VDD pin, and a 1.5µF or greater bypass capacitor for the CAP pin. The CAP pin is connected to the internal LDO. Place these capacitors close to the device pins.
  2. An external reference of 1.8V to 5.5V can be applied to the VDD pin of the device. In addition, there is an internal precision 1.21-V reference with ×1.5, ×2, ×3, and ×4 gain options. If using a noisy supply, it is best to use the internal reference instead of VDD as the reference because noise on the reference translates directly to noise on the output of the TPL1401.
  3. The input signal should not exceed VDD. Also, the maximum threshold voltage is limited by the reference voltage used. If necessary, larger input voltages can be scaled using a voltage divider, and the threshold voltage can be adjusted accordingly.
  4. In this design, the 5-V VDD supply input is used as the reference. The threshold value is set to 2V using the DPOT_POS field of the DPOT_POSITION register. The code programmed to this field, in decimal, is calculated using:
    Equation 1. GUID-20210309-CA0I-CTQM-7QCW-Q5BQVRCGDBWX-low.gif

    With a 5-V reference, unity gain, and a threshold value of 2V, the equation becomes:

    Equation 1. GUID-20210309-CA0I-PVDM-TWDF-C4HWJFFVXC8F-low.gif

    This is rounded down to 102d, to give a threshold of 1.992V.

    Using a 5-V reference and the 8-bit TPL1401, the LSB size, or step size between each code, is about 19.5mV. Using lower reference voltages decreases the LSB size and thus increases the resolution of the threshold value. Using a smaller reference limits the upper limit of the threshold value, but as discussed earlier, input voltages can be scaled down if necessary.

  5. The TPL1401 can be programmed with the initial register settings described in the Register Settings section using I2C. The initial register settings can be saved in the NVM by writing a 1 to the NVM_PROG field of the PROTECT register. After programming the NVM, the device loads all registers with the applicable values stored in the NVM after a reset or a power cycle.