9.2.1 Design Requirements

9.2.2 Detailed Design Procedure

For digital I/O applications, the inputs must be connected to the IN0 - IN9 pins as these are the only inputs that have the current sink necessary to facilitate these type of switches. The external resistor must be sized so that the pin voltage V_INX remains below the max comparator threshold of 4.7 V until the current sink is saturated by the pin voltage. This ensures a low will always be considered a low as the external system voltage V_IN continues to increase. Lower comparator voltages can be used if the external components are sized to ensure that until the current sink is saturated, the voltage remains below the comparator threshold.

To select the resistor for a digital I/O application, ensure the voltage on the IN_X pin (IN0 - IN9) remains below the comparator threshold until the input voltage V_IN is above the OFF region defined by the IEC standard. With a 400-Ω resistor and worst case current of 9.2 mA, a 3.68 V voltage drop is observer across the resistor. This keeps the V_INX 3.68 V below the system input V_IN, ensuring that comparator does not detect a high until V_IN is out of the OFF region and in the ON region.

The second use case for TIC12400 is to monitor analog input voltages from external sensors. These sensors could be a high or low type sensor that has a 1 or 0 representation of the output. In this case, the comparator mode of the input can be used. To ensure correct operation, a voltage divider may be necessary to scale the incoming voltage so that a low will be below the chosen comparator threshold. For reference the available comparator thresholds are 2 V, 2.7 V, 3 V, and 4 V.

For multi level sensor outputs the TIC12400 internal ADC can be used to set to monitor analog input voltages. The following procedure can be used to setup the TIC12400 ADC inputs

1. The first step is to set any input that will be used in a pure analog ADC mode to the 0 mA current setting.
2. The second step is to estimate the voltage output of the sensor. The full-scale range of the 10-bit ADC is from 0 V to 6 V, with 6 V corresponding to the max code of 1023. A resistor divider can be used to scale the input voltage to meet this requirement by using V_IN = V_{SENSOR_OUTPUT} x R1/(R1+ R2) = 6 V max.
3. The next step is to determine if a wake up feature is needed that uses the ADC thresholds. This could be used to wake up the system in the case that a temperature sensor has indicated a potentially damaging temperature that requires system interaction to fix. The TIC12400 can handle two input states on inputs IN0 - IN11, three input states on inputs IN12 - IN17, 4 input states on IN18 - IN22 and 6 input states on IN 23. Every threshold crossing can trigger an interrupt if required by the system. If no interrupt triggers are needed move on to step three.
4. After the measurement is taken, the raw ADC code will be stored in the ANA_STAT registers to be read by the host for interpretation.

Figure 83. Digital IO Switch Input Example

9.2.3 Application Curves

Figure 84. Type-1 Switch with 400-Ω Input Resistor

Figure 85. Type-2 Switch with 400-Ω Input Resistor

Figure 86. Type-3 Switch with 400-Ω Input Resistor