June 12, 2018
|By: Dragan S. Maric, PhD; Reno Rossetti, PhD EE; and Ole Dreesen;
In the work world, supervisors tend to be those who are highly organized and proactive. When a complex project comes up, this type of go-getter is on the case, ensuring that progress milestones are met and making important decisions when it counts.
In electronic systems, supervisory ICs play a similar role, keeping tabs on voltage levels in microcontrollers, FPGAs, ASICs, and other controlling components. Only after the supply rails have settled within specified values do these ICs enable the electronic loads. Simply put, these devices are an analog hero that provides a simple layer of hardware insurance. There are, however, environments in which proper operation of these ICs is difficult. For example, when supervisors need to operate in a noisy environment or a space- or power-constrained application, this simple task can become a challenge. Let’s take a look at some ways to address the challenges faced by supervisory ICs.
External and internal sources cause electromagnetic interference in automotive environments. The “arc and spark” noise that comes from ignition components, motors, and similar pulse-type systems affects the electronics supply rails by producing disruptive undervoltages or overvoltages. When choosing electronic components for a vehicle, noise tolerance or immunity is an important consideration.
Figure 1 depicts a diagram of a microprocessor supervisory IC controlling the car’s remote camera modules, controller area network (CAN), serializer, and deserializer. Each electronic load correctly operates within its specified input voltage range. The operating range of each load is limited by the accuracies of the power supply and the supervisory IC, along with the input-voltage noise amplitude. An accurate supervisory IC will provide more margin against noise. For example, a ±0.5% accuracy advantage on a 3V supervisory threshold will provide an extra noise immunity of 15mV.
Figure 1. In this diagram, a supervisory IC controls a remote camera module, CAN, serializer, and deserializer.
For greater flexibility as well as more margins against noise, the wide VDD input voltage range shown in Figure 1 for the supervisory IC offers a good example.
In portable applications, an accurate supervisory IC can be used to lower the electronic load voltage, saving power. A supervisory IC with an accuracy advantage of ±ε% will enable an extra range of operation of ε%. Consider an electronic load that operates at a minimum voltage, VIN. The same electronic load monitored by a supervisory IC with a ±0.5% accuracy disadvantage will have to operate at a higher minimum voltage 1.005VIN. Its associated power loss (proportional to the square of VIN) will be 1% worse in the latter case. This is the same as lowering the electronic load's power-supply efficiency by 1% point, which is not trivial.
Because of the supply current required for its operation, a supervisory IC may become a significant current drain to a system in sleep mode. However, a supervisory IC designed in a modern CMOS process should reduce the current drawn down to the order of 10µA, minimizing the burden on the battery.
In another example, motion encoders—electromechanical devices that convert the linear or angular position or motion of a shaft or axle to an analog or digital signal—squeeze a lot of electronics into a small space. Figure 2 shows the application-specific standard product (ASSP), power supply, supervisory/POR/OTP, and RS-485 interface subsystem embedded in the encoder.
Figure 2. Encoder ASSP power rails control
In this space-constrained application, the integration of supervisory and protection functions in a small IC package do make an impact. As shown in Figure 3, the MAX16132, MAX16133, MAX16134, and MAX16135 µP supervisors are housed in a small SOT23-8 package. You can see the contrast in size with a similar device housed in a bulky MSOP10. The larger package takes up about twice as much PCB space.
Figure 3. The SOT23-8's size advantage
The MAX16132–MAX16135 µP supervisors are excellent examples of monitoring ICs that address the challenges we've discussed. Learn more by reading our article, "Get More from Your System with a Cutting-Edge Supervisory IC" in Power Systems Design.