Published: December 17, 2024
Table of Contents
Voltage Detector to Monitor When a Power Management IC Fails?
Is There Equipment That Should Never Fail?
Safety by Separating the SENSE Pin!
Pin Layout is Quite Ingenious.
This blog is about a somewhat unusual reset IC (window voltage detector).
One day, Rookie B, in his third year with the company, came to Senpai* A, a senior veteran, with a worried look on his face, ......
*Senpai: A Japanese-style title to show respect to those older than oneself, especially used in organizations such as companies, schools, etc. It sometimes implies that the psychological relation between the two is closer than that between a boss and a subordinate.
Click here to read the previous blogs in the "Help Me, Senpai!" series:
Vol. 1 IoT for Energy Harvesting: Solar Panel Can’t Drive System till Morning…
Vol. 2 Stop Sleeping Mobile Device from Consuming Battery Charge!
Vol. 3 Backup Switchover Circuit Is Not Easy.
Vol. 4 What is AEC-Q100?
Vol. 5 I Would Like to Purchase Samples without Human Intervention.
Help Me, Senpai! Series Vol. 6
Senpai! I came across this unusual reset IC. How exactly does it work?
Unusual? What do you mean by that?
Here it is. It mentions overvoltage and undervoltage monitoring, or something called a "window voltage detector." Is that really useful?
It seems to be designed with functional safety in mind...
Figure 1. Outputs Reset Signal "L" for Both Undervoltage and Overvoltage
Oh, I see what you’re referring to. This IC outputs a reset signal not only for undervoltage detection but also for overvoltage detection.
I get the concept, but does overvoltage mean overshoot? Wouldn't OVP* handle that? Why do we need a voltage detector?
* OVP (Over Voltage Protection): A function that detects overvoltage at the output pin and stops the output to prevent damage.
No, overshoot happens in an instant, so a reset IC might not be able to detect it. This IC is designed for detecting overvoltage caused by some kind of abnormality. That’s why it’s connected to the output side of the power IC to detect the output voltage. If there’s an abnormality in the power source at the previous circuit stage of a power management IC, the OVP of the power management IC can protect itself. But if the power management IC itself fails, it can’t be protected, right?
Figure 2. Basic Circuit Example Using the R3152N
So, does this mean the power management IC, which is responsible for providing a stable power supply, is monitored in case it fails?
Well, yes.
If a power management IC has a power-good output, wouldn’t it be possible to detect abnormalities in it?
That’s one way to do it. However, power-good signals often lack detection accuracy. Plus, if the power management IC itself is broken, the power-good signal might not even be output, right?
Isn't that idea a bit overcautious?
Not at all.
It’s partly about the design philosophy, but there are devices that simply must not fail.
Hmm, but I was taught that "nothing is absolute."
For instance, imagine losing control of your car while driving. That would be a major issue, right?
You are certainly right.
Modern cars are essentially packed with electrical components, relying on countless semiconductors and electronic parts. EVs, in particular, are often called "running electronic devices." If these components malfunction and cause accidents, it becomes a serious problem.
I've heard they incorporate fail-safe designs, redundancy, and other measures to address such issues.
Exactly. Parts are designed to fail in a safe manner, where even if they break, they won’t cause danger. Or, multiple identical circuits are used so that if one fails, the backup circuit can still operate.
I see. So, the reset IC for overvoltage and undervoltage monitoring resets the microcontroller before it malfunctions due to an abnormal output from the power management IC. In this way, it prevents the microcontroller from going out of control, which is a fail-safe design.
That's right. So, I guess this reset IC is intended for cars.
It seems useful not just for cars, but also for manufacturing machinery on production lines.
Yes, exactly. You’re getting the hang of it.
Functional safety, as it turns out, isn’t about designing equipment to never fail. Rather, it’s about ensuring safety through functionality, assuming that parts will fail and providing safety measures when that happens.
Click here to see the functional safety initiatives of Nisshinbo Micro Devices
By the way, this reset IC is not powered by the output of the power management IC. In the case of a car, it is powered directly from the battery.
？
In other words, if it is powered by a power management IC, it would fail if that power management IC failed. Instead, the reset IC is powered directly from the car battery, and the output voltage of the power management IC is monitored by a dedicated SENSE pin. This is a safety design.
Figure 3. Separation of Monitoring Functions by SENSE Pin
I see. So, it’s been well thought out. That’s impressive, especially since it’s a CMOS IC but can still handle car battery voltages. CMOS power management ICs aren’t just for portable devices anymore, are they?
And ......
Is there more? (laughs)
It seems they’ve really paid attention to the pin layout. It looks like they’ve designed it so that even if there’s a short circuit between adjacent pins for some reason, it won’t lead to a fatal issue.
I see that the power supply and ground pins are on opposite sides.
Figure 4. Pin Layout of R3152N
No, that’s not what I meant…
Well, while separating the power supply pin from the ground pin is a basic principle, I’m referring to the fact that the power supply pin and the SENSE pin are on opposite sides. It's ingeniously designed to avoid shorting the power supply and SENSE pins, which could damage the microcontroller or other subsequent circuits. Furthermore, to protect the reset IC itself, the CD pin next to the power supply pin is designed to withstand up to 50V.
I see. It's a delay capacitor pin.
Paying attention to the pin layout means considering the design from the chip development stage. Functional safety needs to be planned from the very beginning. While this might seem obvious, it's actually quite challenging. It's something they can achieve because of their extensive experience.
I see. I understand very well. Thank you very much.
List of Window Voltage Detectors, i.e. Equipped with Overvoltage and Undervoltage Monitoring, for Functional Safety
Series Name Product Description R3152 42V Input Window Voltage Detector R3154 42 V Input Window Voltage Detector with Diagnostic Function R3500 42 V Input 4ch Window Voltage Detector with Diagnostic Function R5116 42V Input Voltage Regulator with Window Voltage Detector
Additional Information ("Failures" in Functional Safety)
Afterword
This is the sixth blog post introducing how our products can help you.
If you have any questions about this blog, feel free to contact us below.