Hello, and welcome to this Battery Management Systems Seminar session. This is the Electric Vehicle Battery Pack Autonomous Management in Park Mode session. My name is Alex Scheuermann, and I'll be the moderator today.

A few housekeeping items before we get started. All participants are muted for the session, so please use the Q&A box to ask any questions you may have. We might have some time at the end of the session to answer some questions as well. Please also chat if you are having any problems hearing or seeing the presentation.

The different windows on the screen are adjustable, so you can make the slide screen bigger or move it around based on your preferences. With that, I will hand it off to Spencer Hu to get started.

All right, can you hear me OK? OK. Thanks, everyone, for joining. Good afternoon, good evening.

So I'm Spencer Hu, the System and Functional Safety Manager in charge of the EV, xEV, EMS solutions in TI. So today we will talk about some of the interesting topics regarding how to manage the battery pack in the parking mode. So before we get started, I will quickly look through the agenda.

So we first start with the basic generic block diagrams, and then we dive into why we're specifically talking about park mode monitoring. And further, there are some comparisons between the traditional and advanced autonomous monitoring. And it relies on three perspectives.

One is how the voltage temperature is monitored, and how the balancing is handled, and how to respond when the fault happens. And then we'll dive into some of the performance products that we have currently and some of the flagship devices. We have some demo slides as well. So without further ado, let's first jump into the block diagram.

So this is a generic block diagram of the BMS system. And if you have designed some of the projects, you can probably relate to this, although there are some subtle differences. So if not, then here's how we look at it. So on the left-hand side is the low-voltage domain. So it is powered by the [INAUDIBLE] battery and connected chassis. And left-hand side of the dashed line is the high-voltage domain. So between the low-voltage and high-voltage, they are isolated by transformer. So [INAUDIBLE] is there.

And on the high-voltage side, you see those green board here. We call it a cell monitor unit, or some people all it cell supervision unit. So this is the cell monitor that the basic [INAUDIBLE]

So the difference here between some of the drawings you have seen versus this one is this is a generic representation. And here it shows two BQ device on one board, and they communicate coupled by transformer, by the capacity on the same board.

But this could also be every ASIC sits on one individual board, and they are connected from board to board by a daisy chain. And this could also be applied to the [INAUDIBLE], as well, if you remove those daisy chain connection. Instead, put the transceiver, the wireless transceiver, here.

So the topic we are addressing today applies both to traditional wired or wireless. I just want to make it clear. And on the [INAUDIBLE] side, this is called the BMU, or some people call it the BCEU. It's basically a boundary control unit. It is used to control all the intelligence of the battery pack, controlling the relays, running algorithm, so and so forth.

OK, so with that being said, jump into the core of the topic, why we talk about the problem. So the thought is this. When the BMS system is up and running, when the driver is driving the car, the car is in full power. And in that time, the BMS microcontroller, which is a very powerful MCU, sitting on the low voltage BCEU takes full control of the system. It runs diagnostic from every FDTI time, and it checks the voltage temperature, and pay close attention to the dynamics inside a battery pack.

So in that time, there is a very good coverage of the system. And what it does-- when their vehicle goes to the parking lot, that actually goes to the shut-out state. And in the early designs, we have seen many vehicles really just turn off that MCU and open the contactor, and the high voltage is disconnected and then sit there.

So as there has been hazards, like catching fires event, from around the way the event, happened over the years. So there are more requirements coming, one from the consumer side-- in order for them to come off the EV, they would like to see that it really becomes more safer. And also from the legislation point of view, we have seen, globally, there are governments pushing, driving the safety standard for batteries.

And here, at least one example, is from the Chinese government, released in 2020. So there's a GB 38031 just released last year. So in here, it specifically called out that before the thermal runaway happened, which would endanger the cabin passenger, before that, five minutes ahead, the BMS system, the vehicle, should be the passenger alert signal, such that they have time to run.

So this is exactly why this topic we're talking today could be helpful because, when the vehicle is in full power, and you can have full monitoring of that, but when parks, if everything goes away, then what is left to monitor the battery pack?

So we first look at how this is managed today in the traditional way. On the left hand side, you see the traditional method. So in general, the traditional method is achieved that MCU is come back alive, say, every hour and two hours, but the real-time clock, where before [INAUDIBLE], we've been hearing different strategies across different [INAUDIBLE].

But the thing of that is, they do sporadic check. So that's why it comes back to check if things good. If it's good, then it goes back to sleep.

But what's the disadvantage of that is, between the check and check, an unprotected unobserved period. You really don't know what's going on. If the battery is exceeding its fairly high ambient temperature, or some cells is going bad, that is not known until the next time as you come back.

So in order to increase the diagnostic coverage, and also pulling some autonomous features to help reducing the MCU wake up frequency-- by the way, the MCU, like the earlier diagram shows, it runs off the low-voltage 12-volt a battery.

So every time MCU comes up, running diagnostic, it would draw some battery from the lead acid battery. So that could deplete at least the acid battery more often than the traditional internal combustion engine pickup.

So we noticed that the EV trouble of [INAUDIBLE] acid battery drains much faster, the shorter life cycle than the traditional internal combustion engine. So this feature [AUDIO OUT] autonomous monitoring is designed to increase the diagnostic coverage, as well as to conserve 12-volt battery. It comes out in three pieces. One is we implement a continuous over-voltage under-voltage, over-temperature under-temperature coverage.

And secondly, we can handle the MCU off-line balancing, that we call autonomous cell advantage with multiple layer protection. Over balancing the temperature is too high in the ASIC cell or the ambient. Last, but not least, we invented a feature called reverse wakeup feature, which enabled the MCU to be awake enough if the VMS device, ASIC, detects any fault, while the MCU is awake.

So I'm going to talk about one by one this. First, the OV and UV, OTUV coverage, so the continuous protection of comparators.

So it's really designed to provide continuous coverage for the voltage and temperature. And the reason we call it a window comparator is because, I think, it has a high end and low end, and I draw a window for the voltage, as well as for the temperature.

So we provide the cell voltage and the GPIO NTC voltage, essentially, the temperature. The user, before going to sleep, it would set the threshold inside the device. So there is a block diagram here. Rest of block, only highlighted what's related to this feature. There is a full color version in a later slide.

So in here we have the comparator, user program the threshold, and then go to sleep. And then the comparator will take over, continuously looking at any fault. So one thing to highlight is this is independent from [INAUDIBLE], as you can see in the next slide.

So we have the cell [INAUDIBLE] path, from the beginning of the [INAUDIBLE], which is the VC0, the VC16. So coming into the AVC, here's one path. And after some of [INAUDIBLE] filters and level shifter, it goes to a different amount, which goes through the over-voltage under-voltage comparator.

And then, this process by digital, if there is any over- or under-voltage, fault. It will trigger fault. And further, if the fault happens, it could propagate through that daisy chain connected to the board, and propagate back to the [INAUDIBLE]. And I have just described the major slides.

Similar concept, for the over- and under-temperature, so besides the main ADC and the redundant ADC, which measure those [INAUDIBLE] active, we have the comparators, dedicated comparators, depending on ADCs to measure-- to protect over- and under-temperature.

So the reason I put this scheduler here is to show, this stop engine runs this scheduler in the wrong order and fashion. So in the picture, 79616, which is a device, [INAUDIBLE], it provides eight GPIOs to monitor the temperature.

And then, this schedule is just checking from GPIO one to eight, and then coming back to check one to eight again for the under-temperature. Over-temperature is the same thing. You check from one to eight, and then this feature relate to the [INAUDIBLE], well, which we'll talk about right after this. This also checked the temperature one to eight, and then circle back to repeat this. This is how we achieve the continuous monitoring of temperature.

OK, now, this is a quick overview of over-voltage, under-voltage temperature as well as coverage. And then we'll talk about some of the balancing features. So the balancing is a critical piece in the battery management, just because the nature of every cell is made complete in the production. There's some variation. The discharge rate and the distribution of thermo [INAUDIBLE] path could age them differently. In order to maximize the energy inside of our pack, we need to do [INAUDIBLE].

So when the MCU is alive, MCU can control a controlled on chip, which is within the dashed line, on chip path to discharge the cell. But when MCU goes off, so how do you do that? So this is when the device, the ASIC comes in.

So there are state machines behind-- within the device that can toggle this path on and off as certain pattern for certain duration of time to discharge the current.

So still, this is preprogrammed by the MCU, and so you set how long I want to discharge the cell, such that [INAUDIBLE] holding a charge. And at what temperature I would like the device to pause the balancing, which is a unique feature to TI solution. As well as, device have some self-protection. But we'll get to that.

So here are two figures to show we're able to balance each cell individually, or we can balance the two cells next to each other at the same time. And here's the equation known as the balancing current. It is the predetermined by the balancing resistor we've designed them for.

So we talk about the thermo. So as you know, we'll do the balancing if every cell we balance at 0.1n, say 100 milliamps. And every cell is 4 volt. You're burning like 0.41 in the system.

And if there are more than 12 or 16 cells, then you would see quite a bit of heat in the system, right? So heat generation and heat dissipation is a lot of considerations. When we design boards, we will put thermal pad for the balancing resistors, as well as your housing.

So we understand that thermo sometimes could go all of these on target. So we want to prevent the balancing goes out of the [INAUDIBLE] boundary. So two features that we introduce, one is when the cell balancing is on, the chip temperature is monitoring.

So we put the temperature sensors near to the balancing vent. If the balancing temperature of the die goes above 105 degrees, we would pause balancing. Then when the temperature cools down, we'll continue.

So this is always on feature. You can think about this as, it's the right temperature comparator inside the [INAUDIBLE]. And the other way we manage this is there are some other hot spot inside a system of PCB, so those balancing resistors.

So we can provide a feature that puts the MTC next to the balancing resistors and use that temperature as a reference to pause the balancing or resume, just like what we said on the cylinder. The difference now is we monitor the off-chip temperature to pause and resume the balancing.

OK, so the balancing scheme we support of autonomous balancing, so this pre-programs by the MCU how long you want to continue, and what is the under-voltage threshold you want to stop. It is like a preventive method. If the cell voltage under 3.8, I do not want to continue balancing anymore, right. And the thermal pause is what we described in the last slide. And then, when MCU is active, let's say, in the active mode, if a car's driving or travelling, MCU can take the full control of the balancing this variable. If not, to always use the auto [INAUDIBLE].

Here, so here is just a quick diagram to show how the current is flow across odd and even channels. So in autonomous balancing, up to 10 hours, we support odd and even balancing. If there's only odd channel that is unbalanced, you can always just turn on odd channel, if even channel not on.

So this gives a quick overview of the balancing feature. So how we balance and what our thermo considerations features that enable our customer to better manage the thermo in the housing, as well as some of the control scheme.

Next one is the third piece of the autonomous balancing is called the reverse wakeup. So reverse wakeup is what we invented when we first designed this group device, BQ79600, together with the BQ796XX device.

So what is really does is exactly to solve the issue that, between the MCU spot check, there is no coverage of the battery pack. And MCU doesn't know if temperature is normal, the cell voltage is normal, even though your contactor is opened, there's no current drawn from the load.

But if there are any defects in the battery, in voltage control, and this feature allows us to catch all those on the fault. For example, if BMU the five controllers, the SBC, and BQ79600 and the group device are all in the shutdown-- we've noted in black color.

And then we leave the BMS ASIC in the sleep mode, either doing the balancing, or doing the balancing as well as monitoring the cell voltages. If there's any over-current-- I'm sorry, over-temperature or under-voltage event happens, or over-voltage probably is less likely, since we've [INAUDIBLE], this device detects a fault.

Then this fault will be locked in the register, and then we will generate a fault communication [INAUDIBLE] to the next device. And once this device detects a fault problem, we'll do the similar things, propagate to the next device, and so on and so forth, until this fault problem is propagate back to the root device, the BQ79600.

And once the BQ79600 detects a fault, it will wake up and validate, hey, if this is real fault or this is just noise. Once this is validated, it will send a signal to enable the PMIC through the inhibitor. It's similar to like CAN transceiver concept.

You can enable pinning. Once the pin comes up, it will wake up MCU, and MCU knows, OK, if there's an unexpected wake up, let's see what's going on. And then we'll do that, mostly to see how [INAUDIBLE]. And then the system can take the control from that point. So this really ties everything together, how we manage the data pack in a sleep mode.

Now, we talk about a couple of devices here, right? So we talked BQ796XX and BQ79600. I'll show this in our problem.

So TI actually has been in the automotive BMS market since 2010. And this is the fourth generation of our battery more to ASIC.

So we started in a six channel, PR536, and then 16 channel PR455. So back in the days, before EVs, as popular as today, the functional safety is not quite there. Starting from the third generation that were designed, the PQ79606 is starting from [INAUDIBLE] device.

And then, last year, we released the MQ79616. It's a 16 channel, high accuracy battery management in ASIC, doing balancing protection. And this device is the core device, and from this we also develop a few subsequent for this core.

We can support the 48-volt system as well. And we also can have a device that provide a current sensing. We have seen some interesting applications in the budget platform. So it can combine the wire sensor with this device.

So besides the 16 channels, we provide the pin-to-pin compatible, as well as [INAUDIBLE] cell compatible solutions, 14 and up, and the companion chip that communicate between the MBS ASIC as well. And the MCU is this communication standard, BQ79600.

So if you're interested in this device, please reach out to our sales market or reach out to us. We have the full data sheet available for this device. So this is the volt diagram I mentioned earlier. Some of the main building blocks that was listed here.

I don't need to go into the details. But I do want to show this. So together with the EVN, we come up with this evaluation GUI. It's a software that you can access from your PC through USB to any cable connected to here, to here.

And so this GUI enables you to exercise playing around with the features come with the device. Either the cell monitoring or the cell balancing, this diagram shows the cell monitoring. So we have 16 channels and can look at different temperatures at some different voltages. And some of the system faults, if any, and it will go to the red color.

So if you need any samples, later, if you can find a PDF version of these slides, you can click here for examples. Or you just go to TI.com and search PQ79616.

OK, so with that being said, we've come to the end of this presentation. And we can open up for any questions.

Thanks.

So thanks, Spencer, for the presentation. And thank everyone for joining us today. You're going to receive an email with a link to on-demand recording of the session. And there's going to be a brief post-event survey that pops up after we end.

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