Table 9-4 Example Resistor-Coded Switch Specification | SPECIFICATION | MIN | MAX |
---|
VBAT | 9 V ≤ VBAT ≤ 16 V | 9 V | 16 V |
R1 | 680 Ω ± 8% | 625.6 Ω | 734.4 Ω |
RSW1 | 50 Ω Max when closed | 0 Ω | 50 Ω |
RSW2 | 50 Ω Max when closed | 0 Ω | 50 Ω |
RDIRT | 5000 Ω Min | 5000 Ω | ∞ |
VGND_SHIFT | ±1 V | -1 Ω | +1 Ω |
An example of a 3-state resistor-coded switch is shown in Figure 9-6, with Table 9-4 summarizing its detailed specification. The goal of this design is to utilize the TIC12400-Q1’s integrated ADC to detect and differentiate the 3 switch states:
- State 1: Both SW1 and SW2 open.
- State 2: SW1 open and SW2 close.
- State 3: SW1 close and SW2 open.
To mimic real automotive systems, the battery is assumed to be fluctuating between 9 V and 16 V. R
DIRT is introduced to model the small leakage flowing across the switch in open state. There is also a ±1 V ground shift present in the system, meaning there could be up to ±1 V of potential difference between the switch reference point and the ground reference of the TIC12400-Q1. When the switch changes position and the switch state changes from one to another, the TIC12400-Q1 is required to correctly detect the state transition and issue an interrupt to alert the microcontroller. The switch information needs to be stored in the status registers for the microcontroller to retrieve.