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Automotive TI Tech Days 2020 - Power management sessions TI’s intelligent LED drivers in automotive cluster systems
Automotive TI Tech Days 2020
2.1 TI’s intelligent LED drivers in automotive cluster systems
So, Matthew, shall we start?
Yeah. Do you want to wait, maybe, just 30 more seconds, or do you want to just get going?
OK, no problem.
Just in case people are having problems with Webex. So we'll get started in one minute.
We've got some people trickling in. All right. We're one minute past, so let's go ahead and get started. OK. Hi, everyone. Welcome to TI's automotive, virtual tech day this year. This is the TI intelligent LED drivers for use in automotive cluster systems session, [INAUDIBLE] Shirley He.
My name is Matt Guibord. I'll be the moderator for the session. As a reminder, all participants are muted. So if you have any questions or comments, please use the chat function, and we'll be monitoring it throughout. And with that, I'll hand it off to Shirley to get started.
OK. Hello. My name is Shirley He. I'm an applications engineer from the Texas Instruments LED drivers team. The topic of my presentation today is, TI's intelligent LED drivers in automotive cluster systems. This presentation is a product overview of the TI LED driver solutions in automotive instrument and cluster system design.
Here is a video agenda on this session. First, we'll take a look at the automotive instrument cluster system trends and see what LED drivers TI can provide in the cluster systems. Then, we'll go into the details on the three types of LED drivers in cluster systems, including the automotive LED indicator, the LED in global dimming backlight, and the LED drivers used in local dimming backlight. After that, we will show how we can aid customers with the [INAUDIBLE] safety system design.
This figure from the Strategy Analytics-- the amount of [INAUDIBLE] for different types of cluster systems. We can see, after the decline in 2020 due to the effect of the COVID-19, the demand for high-level-- for high-end cluster-- hybrid cluster featuring the natural display sizes-- and the demand for [INAUDIBLE] solid state clusters will continue to increase.
The high-end [INAUDIBLE] hybrid cluster [INAUDIBLE] analog gauges, plus a display panel of more than five inches. We can see that demand is still increasing. The solid state cluster is now the [INAUDIBLE] section of the cluster market. It can be conventionally driven by its own ECU or [INAUDIBLE]. The CDC here refers to the centralized cockpit domain controller, that also controls the climate controls and the infotainment systems.
For both hybrid clusters [INAUDIBLE] clusters, [INAUDIBLE] are always required in the system. For the hybrid clusters, since it uses the smaller LCD panel, no power backlight LED driver is required. In a multiple channel, LED indicators are required to light up the LEDs under the analog gauges, as well as the tell-tales. The tell-tales include warning lights for safety critical, [INAUDIBLE] inner functions. Sometimes it also includes indicators for gear selection and [INAUDIBLE].
For the solid state clusters, a larger sized LCD panel is used so that a high power backlight LED driver is needed. The tell-tales can be displayed within the display panel in some clusters. We also see some tell-tale signals are kept separate from the display panel for functional safety requirements, as this picture shows. So solid state clusters may also need LED indicators for tell-tale functions.
TI can provide whole solutions for all kinds of LED drivers required in the cluster system. We will go through these devices in the following sections. In a typical hybrid cluster, a typical [INAUDIBLE] of LEDs to be driven independently. If each LED is controlled by the GPU of the MCU, too many GPU hours are used.
And it's also not easy to do the constant current control and LED diagnostics. Compared to the [INAUDIBLE] solutions, TI providers are [INAUDIBLE] which can support a serial interface in a daisy chain mode, so that most GPU hours can be saved.
[INAUDIBLE] multi-channel automotive LED indicator family. The devices in the middle use simple on off control with a simple diagnose. Constant current cannot be achieved with these devices. The breakdown voltage of these devices is 40 volt. So the LEDs can be collected to the battery direct resistor to an image of the current. The devices on the right side can do constant current regulation and offer full diagnostics. The breakdown voltage is [INAUDIBLE] so that a DC-DC converter is required to provide the supply voltage.
Recently we see more and more instrument cluster systems requires the functional safety compliance, especially for the tell-tales, which offer requests [INAUDIBLE]. So the safety-related features for the LED indicators are quite important. So I'd like to introduce the diagnostic and protection features of some [INAUDIBLE] products in detail.
For the device category without constant current regulation, I will take the TLC6C5816 as an example. This is a 16-channel device, which has 16 outputs. 8 out of the 16 channels can be configured to LED open and short diagnostic, so it's very flexible to use. The device also supports serial interface communication for error detection. It also has an open-drain error for MCU interruption. So this is quite a simple and no-cost device, which can perfectly replace the [INAUDIBLE] solutions.
Moving on to the constant current device, TLC6C5712 is a constant current device, which has the most comprehensive diagnostic features. So it is most suitable for safety-related applications. First, this device has independent short LED detection for each channel. It is also able to distinguish the LED open-load for-- LED short-to-ground fault, by having an internal [INAUDIBLE] current to [INAUDIBLE] during the PWM off state. These LED faults can be [INAUDIBLE] states, so that the LED faults can be detected before the faulty channel is turned on.
[INAUDIBLE] also provides [INAUDIBLE] with supply detection to avoid reporting a false fault due to the supply failure. [INAUDIBLE] adjacent pin short detection is also supported. If any two adjacent pins are shorted, the fault can be reported. This detection [INAUDIBLE] when outputs are disabled. This is useful for some associated safety co-evaluation given a good pin FMA. Following are some general diagnostic features including reference resistor open, pre-thermal warning and shutdown, input PWM timeout, open-drain error report.
For the error pin, the device provides the force error command to put down the error-- open-drain output to simulate a faulty scenario. With this command, the error pull-down feedback circuit can be validated without a real fault. Since the fault of error feedback in the control circuits contribute to the latent fault [INAUDIBLE]. The latent fault metric can be reduced by using this feature.
Now let's take a look at the diagnostic feature of another constant current device, TLC6C5724 and 16. Like the previous 12 channel device, the 24 or 16 channel device also provides a variety of diagnostic features, including LED short, LED open, and output short to ground, adjacent pin short detection, and so on.
Besides that, there are two unique features in this device for safety consideration. First, is the LED open and short detection circuit self test. The self test function can check the internal LED open or short detection circuit to improve the system reliability. If the detection circuit fails to detect the LED failure, the self test function can identify and report the fault.
The device also has-- implements a negate bit toggle-- negate bit toggle function to check the LED open and LED short register error. Since the faults in the LED open and LED short detect [INAUDIBLE] in the registers, [INAUDIBLE] can be considered as latent faults. These two functions can help to address the latent fault metrics as well.
Well, these are the introductions about the LED indicators. Now, let's move on to the backlight LED driver. [INAUDIBLE] we can see clusters are moving towards bigger screens with a better user experience. For both the hybrid cluster and solid state clusters, a TFT LCD is a main technology in display panels. Several methods for backlighting the LCD panel using LEDs, edge lit or direct lit backlight.
For edge lit, LEDs sit around the edge of the screen with a special diffusion panel and a light guide to spread the light evenly behind the screen, which we call global dimming. For direct lit backlight, LEDs [INAUDIBLE] directly behind the screen. The LEDs behind the LCD layer adapt to the picture displayed, which we call local dimming. Local dimming can improve the contrast ratio. One part of the picture to be displayed is black. It makes blacks appear deeper and darker on those parts of the screen.
Let's look at the global dimming [INAUDIBLE] first. TI provides a whole family of global dimming backlight LED drivers. The devices can be divided into two categories, depending on using external FETs or internal FETs. We have three channel, four channel, and six channel options. [INAUDIBLE] internal FET solutions are used in small size panels or where a simple diagnostic is required. External FET solutions can handle bigger power, which can be used in larger sized panels with higher brightness requirement, or applications with higher safety requirements, such as cluster, mirror replacement system, head-up display.
Our latest external FET device is the LP8866 and 64. The LP8866 is a six channel device with a channel current up to 200 milliamp. It is the most powerful and robust backlight LED drivers in our roadmap.
It offers several benefits, such as-- can support high brightness and big size LCD panel. It has good cold cranking behavior, and good EMI performance, and it is easy for customers to use. If you look at [INAUDIBLE] circuit of the LP8866, the configuration is a boost controller plus six channel countersinks. The charge pump is used to support input voltage down to three volts. The booster of frequency and other settings can be set via the external resistors, so it's quite easy to use. The I-squared interface is implemented for easy communication.
This page lists all the fault types the LP8866 device can handle. There are three main fault types in total. Supply faults include the VIN undervoltage, overvoltage, overcurrent, VDD undervoltage charge pump fault, clock fault, or register CRC fault. The boost faults include the boost OVP, OCP, the resistor detection fault, and thermal shutdown.
The device can also handle all kinds of LED faults, including the open LED string, shorted LED, LED short to ground fault. All the fault status registers can be read back from the their respective fault registers. The faults marked in red means critical faults, which will make the chip enter the fault recovery state. It will shut down all the modules and then retry periodically. The power line fault before the boost is also shut down under these critical faults, for safety consideration.
The LP8866 device contains several diagnostic registers [INAUDIBLE] debugging or additional device information. For example, the current state of the data machine can be read back through the FSM_LIVE_STATUS. The boost output can be read back and calculated with the VBOOST_STATUS register.
16-bit LED PWM [INAUDIBLE] and 12-bit LED current DAC calculated by the internal dimming mechanism can be read back in two registers, so that the internal brightness control pass can be validated. The bottom four registers can be read back to verify if the [INAUDIBLE] right configuration and operates with the [INAUDIBLE] settings, including booster frequency, PWM frequency, and so on. Diagnostic features [INAUDIBLE] the functional safety random hardware failures assessment under certain conditions.
An important LED diagnostic feature [INAUDIBLE] is the LED short to ground fault. This is the first device in our family which can support the LED short to ground detection. It supports the industry's quickest LED short to ground fault detection.
During the boost self-start or normal boost operation, if one of the LED output voltage is lower than the short to ground threshold, 0.24 volts typical for more than 20 milliseconds, the device will turn off the corresponding LED output channel and the [INAUDIBLE] current on the output pin with a short period. After this operation, if the output voltage is still lower than the headroom voltage, the LED short to ground [INAUDIBLE].
This implementation is able to distinguish the LED short to ground fault from an LED open fault. With this feature, it can avoid the glare when [INAUDIBLE] to ground, and the risk of blinding the driver at the light, which is quite important for the cluster application.
Another factor about this device is the way you arrange the pin order. The pins in red are high voltage reading pins. The pins in green are low voltage [INAUDIBLE]. We separate all the high voltage [INAUDIBLE] from the low voltage pins with the ground, or NC pins. The device has to be validated to be able to survive when any pin is open, or short to ground, or [INAUDIBLE] the pin, which offers a robust design with high reliability. We have also prepared a pin FM error report to help with the functional [INAUDIBLE] analysis.
Besides global dimming backlight, local dimming is an emerging technology we see in recent new projects. This page shows the basic local dimming architecture. Compared with global dimming, the TCON should be able to process both video stream and backlight control signal. The LED backlight are divided into maybe hundreds of zones. Each zone contains at least one LED. The output current of LEDs in different [INAUDIBLE] be individually controlled. The LED driver should be able to support a cascaded digital interface.
To achieve the channel individual control, each zone can be directly driven or scanned, which we will discuss in detail later. TI provides direct drive solutions. Our device is compatible with the common local dimming TCON in the market and support the unlimited device cascading.
Now, let's look at the comparison between the direct drive and the scan methods. For direct drive, all the LEDs are driven at the same time, in parallel. One LED backlight-- one backlight zone needs one LED driver's channel, which is quite a step forward. So the total required output channel and LED driver device count is big.
Moving on to the scan method, the backlight LEDs are driven sequentially in groups. LED multiplexing used where LEDs are collected in metrics, with controls of rows and columns to separate driver channels. Each column get collected to the LED driver current syncs, and additional switches and circuits are used to control the [INAUDIBLE].
[INAUDIBLE] architecture, there will be high peak current for each LED in the LED driver's channels, since each LED could only be driven in a duty cycle. For example, if a four multiplexing is used, the peak current is more than four times higher than direct drive, due to the nonlinearity between the LED and luminous intensity and the forward current. So the total power consumption is also bigger, compared with direct drive solution.
[INAUDIBLE] the power consumption of the LED driver in the two methods. For the scan method, one LED driver can control more LED channels, and the average current for each channel is higher than direct drive. So each LED driver will consume more power. If put on the [INAUDIBLE] it will be a hotspot which [INAUDIBLE] concern. So it's really unfeasible to put the multiplexing LED driver chip together with the LED on the LED board, while it's OK for a direct drive device to be placed on the bottom of the LED board.
On the other hand, now that it's unfeasible to put the multiplexing LED drivers on the [INAUDIBLE]. If we put the LED drivers on the control board, the control board will need more PCB space, bigger collector, and cables with more conductors to connect to the LEDs on the LED board, which will add much more cost.
Given all these analyses, TI [INAUDIBLE] method for [INAUDIBLE] backlighting. [INAUDIBLE] 48-channel device, TLC6C5748 to solve the higher channel count requirement in local dimming application, so that the cost per channel is reduced.
This is an overview of this device. It can drive 48 LED zones. [INAUDIBLE] in the previous slides, direct drive offers the perfect solution for chip-on-LED-board architecture. Direct daisy chain interface with TCON controller can be supported. The maximum current for each channel is 32 milliamp. The maximum voltage is 11 volts. So three single-junction LEDs or one dual-junction LED in series can be supported. [INAUDIBLE] reduces the system power consumption, reduces system cost, and supports unlimited device cascading.
Using the new 48 channel device, which has to develop a reference design, which use [INAUDIBLE] devices to drive 384 zones and LEDs. The eight LED drivers are placed on the bottom of the [INAUDIBLE]. And the similar performance is also evaluated to be good. For more details about this reference design, we will have a dedicated presentation at 11:00 tomorrow in the automotive systems station, where the presented [INAUDIBLE] local dimming backlight feature in detail.
In the end, we'll talk about the functional safety topic, as well as the traditional tell-tales. There is also increasing requirement to present new safety-critical information to the driver. For example, from the development of new [INAUDIBLE] features. So the functional safety requirement on the LED driver may increase as well. We have already released [INAUDIBLE] safety-capable device-- LED driver devices on TI.com and provided documents to aid the system-level functional safety cluster design.
We can provide the following documents, including the functional safety FIT rate, failure mode distribution. For some devices, we also provided the Pin FMA and diagnostic description and fault handling routine. Our target is that, for all the recently released or future automotive LED drivers used in cluster, we are always provide these documents to aid customer's system functional safety design.
So much for my presentation. If you have any questions, please feel free to ask using the chat function.
Thanks, Shirley. Yep, so if there's any questions, please use the chat function to send them.
I see, here, we have a question. Is functional, safe, compliant LED indicator device, that is developed according to ISO 26262. Actually, no. Right now, we don't have any LED driver device that can meet the component enabled functional safety. Actually, for a functional safety required system design, not all the hardware elements need to be developed according to the ISO 26262. [INAUDIBLE] can provide the documents to help customers achieve system-level functional safety requirement.
OK, and there's no other questions. And I think we'll go ahead and close the session. So thanks, Shirley.
Thanks, everyone, for joining. All session recordings and presentations will be available to download next week. You'll receive an email with links and a post-event survey. So we'd like your feedback, so we can continue to improve our content for future tech days, maybe in person next time, and other training events. So thank you, again, and have a great rest of your day. Look forward to seeing you on additional sessions.
Ah, Shirley, there is one question that just came in, if you want to answer this real quick.
New to driver [INAUDIBLE], are large LED arrays becoming common in automotive cluster applications?
Can you repeat that?
Yeah, the question is, are large LED arrays becoming common in automotive cluster applications?
Yes. We have seen the low dimming requirement of several projects now, and we expect to see more projects request the local dimming architecture.
Yeah, so I think, it's trying to understand an example application for a 48-channel LED array. So when it comes to local dimming, can you give an example of what a locally dimmed cluster might look like?
Yeah, for the local dimming, it will control the LEDs individually, according to the picture to be displayed. So if some of the picture is back, they reduce the brightness of these beneath the picture so that the contrast ratio can be improved.
And it would be different sections of the display that you'd want one brighter [INAUDIBLE] the other dimmer.
Could you maybe go-- I think you had a slide on an example cluster for the local dimming. Ah, here we go.
Yes. The light behind the--
I think the question is really-- it's at the high level.
So if you were sitting in your vehicle looking at this cluster, why would one section of the cluster be brighter, versus another section of the cluster be dimmer. Is it different gauges, for instance, or--
Yeah, the light behind the LCD will adapt to the pictures displayed. So if the picture here is black, this will make the blacks appear more darker and deeper for this-- from the driver's point of view.
OK. Yeah, that's clear to me. Thank you, Shirley.
OK. The next session will begin in-- I'll click 23 minutes, not an hour.
August 24, 2020
In this session we will introduce our portfolio of LED drivers for typical LED and backlighting applications and how we’re meeting the increasing requirements for automotive cluster systems. The TLC6C5816-Q1 and TLC6C5712/24-Q1 are multi-channel, intelligent LED drivers with LED open/short diagnostics to ease system design. The LP8866-Q1 is a backlighting LED driver with the power to drive any-sized LCD panel and provides full system diagnostics.