SLAAEU1 August   2025 MSPM0L1306 , MSPM0L1306

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Hardware Connection
  6. 3LaunchPad Setup
  7. 4Software Structure
  8. 5Design Considerations
    1. 5.1 IO Selection Consideration
    2. 5.2 Y-axis and X-axis Measurement Method
    3. 5.3 Touch Detection Method
  9. 6Evaluation Steps
  10. 7Summary
  11. 8References

5.1 IO Selection Consideration

In Figure 2-1, two IOs are used for Y-axis direction drive and one IO is used for X-axis drive. There are two considerations to remember:

  1. MSPM0 IO current output and input limitation
  2. MSPM0 IO internal resistance

The resistive touch screen has 700ohm resistance in x-axis and 300ohm in Y-axis. Use 3.3V as the system power supply. That means users need 11mA to drive the resistance in X-axis, and need 4.7mA to drive the resistance in Y-axis. The MSPM0 L1306 current limitation is 6mA as shown in Table 5-1, and can be found in the data sheet. If users go beyond the specification, then permanent damage on MSPM0 can occur. That is why TI recommends to use two GPIOs to drive the Y-axis and one GPIO to drive the X-axis.

Table 5-1 Absolute Maximum Ratings
PARAMETER TEST CONDITIONS MIN MAX UNIT
VDD Supply voltage At VDD pin –0.3 4.1 V
VI Input voltage Applied to any 5V tolerant open-drain pins –0.3 5.5 V
VI Input voltage Applied to any common tolerance pins –0.3 VDD + 0.3 (4.1 MAX) V
IVDD Current into VDD pin (source) -40℃ ≤ Tj ≤ 130℃ 80 mA
Current into VDD pin (source) -40℃ ≤ Tj ≤ 85℃ 100 mA
IVSS Current out of VSS pin (sink) -40℃ ≤ Tj ≤ 130℃ 80 mA
Current out of VSS pin (sink) -40℃ ≤ Tj ≤ 85℃ 100 mA
IIO Current of SDIO pin Current sunk or sourced by SDIO pin 6 mA
Current of HSIO pin Current sunk or sourced by HSIO pin 6 mA
Current of ODIO pin Current sunk by ODIO pin 20 mA
ID Supported diode current Diode current at any device pin ±2 (1) mA
(1) Stresses beyond those listed under Absolute Maximum Rating can cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Condition. Exposure to absolute-maximum-rated conditions for extended periods can affect device reliability.

MSPM0 internal IO resistance causes an offset on the resistive screen detection. For some high-resolution applications, this is not acceptable. If users want to reduce the influence, then there are two methods to further improve performance.

  1. Add more IOs to drive the screen to spread the load current to more IOs pins.
  2. Add ADC to both positive and negative axis IOs. Directly measure the voltage assigned to the IO internal resistors when driving the screen.