Use multiplexers to optimize protection and accuracy characteristics in servo drive control modules

When designing a reliable servo drive control module, accuracy and protection characteristics are essential to ensure reliable operation. If these characteristics are not taken into account during the design process, it may cause wrong readings or damage to the analog-to-digital converter (ADC) or microcontroller, thereby reducing system efficiency or causing downtime.

Regarding accuracy and protection, think about penalty kicks in football. The accuracy of the shot or the goalkeeper’s performance may determine the outcome of the game.

When the servo drive has hot-side control or cold-side control, the ADC and multiplexer are used to measure the three-phase ground voltage and DC link voltage. Accuracy is the most important, it is related to whether the motor drive can have the correct torque, speed and position in the servo drive controller.

Choosing the “right” multiplexer will help prevent errors or false readings while helping to optimize system efficiency. An 8:1 single-channel multiplexer (such as TMUX1108) can provide accurate data input to the ADC with low on-resistance, low on-capacitance, and low leakage current. These features allow the MCU to get accurate feedback to achieve the correct torque, speed and positioning of the motor drive system.

In the servo drive control module, there are many situations that can cause unnecessary reverse power supply and damage the downstream of the signal chain. Overvoltage events are one of them. Applying voltage to the digital or analog interface before the entire device is powered up may also cause erroneous readings or provide input voltage when the device is turned off. In Figure 1, the analog sensor sends a 3.3V signal to the switch input when the switch is off. The 3.3V signal reversely powers the unpowered switch through the electrostatic discharge diode, and the switch is accidentally turned on.

Then, the useless 3.3V signal is sent out through the switch, which damages the ADC or causes an incorrect reading. When the switch is not powered on, if there is an input signal on the input/output (I/O) pin, the multiplexer with shutdown protection feature will protect downstream components without causing any unnecessary signal attenuation.

Use multiplexers to optimize protection and accuracy characteristics in servo drive control modules

Figure 1: 3.3V signal to reverse power the multiplexer

In Figure 2, a switch with a shutdown protection feature maintains a high impedance state on the I/O pin to prevent reverse power supply, while a switch without a shutdown protection feature allows useless signals to pass.

Use multiplexers to optimize protection and accuracy characteristics in servo drive control modules

Figure 2: Signal switch with and without shutdown protection

The 1:1 four-channel multiplexer (such as TMUX1511) has a shutdown protection feature to help ensure that the multiplexer is powered on before applying the serial peripheral interface signal at the microcontroller or ADC input . For more information on using a multiplexer to control power timing, please refer to the application manual “Using a shutdown protection signal switch to eliminate power timing.”

Finding the correct multiplexer with protection and accuracy characteristics can prevent problems in your servo drive control module or your entire system. Just like in football, the accuracy of the shot or the performance of the goalkeeper may determine the winner or loser of the game.

The Links:   KCS057QV1AJ-G23 MG400H1FL1

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