SCPS269 September 2017 TIC12400
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
The TIC12400 is an advanced 24-input Multiple Switch Detection Interface (MSDI) device designed to detect external switch status and voltage levels by acting as an interface between the switches and the low- voltage microcontroller. The device offers a number of unique features to replace systems implemented with discrete components, providing board space savings and reduced bill of material (BOM). The device can also be configured into low-power polling mode, which provides significant savings on system power consumption. The TIC12400 is also suitable for many types of data acquisition systems with its integrated ADC, serialization, and digital communication capabilities.
The input stage of the TIC12400 is designed so that for an input resistance of 400 Ω on the IN0 - IN9 pins, the 10 mA current sink setting can be used for IEC61131-2 Type1, Type 2, and Type 3 switches.
Figure 82 depicts how the TIC12400 is used in a multiple purpose application with Digital IO Switches an analog sensor inputs using both the internal comparator and the ADC.
|VSUPPLY||6.5 V ≤ VSUPPLY ≤ 18 V||6.5 V||18 V|
|RIN||400 Ω ± 10%||360 Ω||440 Ω|
|ISINK||10 mA||9.2 mA||13.4 mA|
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 VINX 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 VIN 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 INX pin (IN0 - IN9) remains below the comparator threshold until the input voltage VIN 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 VINX 3.68 V below the system input VIN, ensuring that comparator does not detect a high until VIN 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