SCDA054 June 2025 TMUX1308 , TMUX1308-Q1 , TMUX1308A , TMUX1308A-Q1 , TMUX1309 , TMUX1309A
3 Settling Time Tests and Results
The TMUX1308A-Q1 is the next generation upgrade over the TMUX1308-Q1. This is a direct drop in replacement with improved current injection control and faster settling time. To show this, lab measurements were gathered comparing the worst-case settling time of the TMUX1308-Q1, a common competitor device, and the TMUX1308A-Q1. Test setup shown in Figure 3-1.
Figure 3-1 Lab Measurement SetupThe test conditions used for the experiment were the same for all three devices. There was 10V on the input with two resistors of the same value creating a voltage divider that reduces the voltage in half. Measurements are collected with the resistor values 4.7kΩ, 10kΩ, 22kΩ, and 47kΩ. The capacitance is fixed at 100pF. The device is powered by 5V, two of the address pins A1 and A2 are grounded, while A0 has a square wave input to toggle the two sources continuously. Lastly, the drain pin is probed to show the settling time of the signal. As seen from Table 3-1, the TMUX1308A-Q1 outshines the other two parts.
| R1(Ω) | R2(Ω) | Cs (pF) | Vs (V) | VDD(V) | TMUX1308A-Q1 tst (µS) | TMUX1308-Q1 tst (µS) | Comp-1 tst (µS) | |
|---|---|---|---|---|---|---|---|---|
| Condition 1 | 4.7k | 4.7k | 100 | 10 | 5 | 3.5 | 5 | 4 |
| Condition 2 | 10k | 10k | 100 | 10 | 5 | 4 | 10.5 | 11 |
| Condition 3 | 22k | 22k | 100 | 10 | 5 | 7.5 | 15 | 15 |
| Condition 4 | 47k | 47k | 100 | 10 | 5 | 11.5 | 24 | 22 |
The following images show a settling time comparison between the three devices in voltage and 12-bit ADC error bits over time. In the voltage vs time graphs, the TMUX1308A-Q1 slightly dips and then recovers much faster than the other two devices. Resulting in a small and short disturbance in the voltage signal read by the ADC. Compared to the other two multiplexers, the TMUX1308A-Q1 greatly reduces the voltage distortion imparted on the sensor output signal being measured by the ADC. In the ADC error bits vs time graphs, the error amount is much lower compared to the other two parts. This is due to the fast recovery of the signal from the TMUX1308A-Q1.
As mentioned earlier, since this is a zone & body control module application the voltage supply can go up to 60V. This can result in requiring a current limiting resistor (Rlim) to prevent too much current feeding into the clamping circuit. To limit the voltage down to an operable condition, different resistor values need to be used for different voltage input levels.
| Vinput(V) | Rlim(Ω) |
|---|---|
| 12 | 1.6k |
| 18 | 3k |
| 19 | 3.3k |
| 24 | 4.7k |
| 36 | 10k |
| 48 | 13k |
| 60 | 15k |
Using the 36V input condition as an example, a 10kΩ limiting resistor needs to be implemented. With this resistor, the TMUX1308A-Q1's settling time is reduced to 4uS.
Figure 3-2 4.7kΩ Voltage Settling Time
Figure 3-4 10kΩ Voltage Settling Time
Figure 3-6 22kΩ Voltage Settling Time
Figure 3-8 47kΩ Voltage Settling Time
Figure 3-3 4.7kΩ 12-bit ADC Error Bits Settling Time
Figure 3-5 10kΩ 12-bit ADC Error Bits Settling Time
Figure 3-7 22kΩ 12-bit ADC Error Bits Settling Time
Figure 3-9 47kΩ 12-bit ADC Error Bits Settling Time