Optoelectronics
(LM), is situated outside of the lamps. It’s commonly known as the LED control module (LCM). The LCM often employs the CAN bus to communicate and monitor the status of the LM, including features like animation and brightness. Inside the LCM, buck-boost topologies are frequently used as LED drivers, allowing them to accommodate different LM configurations, such as 6 or 12 LEDs in a single LM. In Figure 1, the LED driver within the LCM comprises both voltage and current sources. Typically, the voltage sources adjust the battery voltage to a higher level, determined by the number of LEDs, while the current sources deliver a consistent current to the LM and lower the boosted voltage. The automotive exterior front lighting system has several lighting functions, including a low beam headlamp (LB), high beam headlamp (HB), daytime running light (DRL), front position lamp (PL), and turn indicator. Depending on the specific lighting functions, the LM is set up with varying
Figure 3. The MAX25608 LED open detection (Channel 2: Drain voltage; Channel 3: FLTB; Channel 4: LED current).
numbers and colours of LEDs. This means the LCM must provide the appropriate current source to regulate brightness. To save costs, manufacturers might integrate two or more lighting functions into a single LM, like combining daytime running light and front position light.
Figure 4. The MAX25608 LED short detection (Channel 2: Drain voltage; Channel 3: FLTB; Channel 4: LED current).
The LED matrix managers, such as the MAX25608, are used to control LEDs individually with different dimming scenarios, such as welcome functions and a wiping indicator. The LED matrix managers consist of multiple switches that can be independently programmed to bypass the LEDs across each of the switches in the string. Each switch can be turned fully on, fully off, or dimmed with or without fade-transition mode. The dim frequency is set by an internal oscillator or set to an external clock source.
Figure 5. An example of a write command.
Smart lighting function: ADB The ADB systems are a smart HB control system that can adaptively adjust the beam pattern based on driving conditions. The full high beam can be distracting to oncoming drivers and pedestrians. The adaptive capabilities of an ADB system can automatically turn the bright lights off or partially beam to avoid dazzling drivers and pedestrians. Based on different headlight resolution requirements, the LM of an ADB system would consist of four or more LED matrix managers to control four or more LED zones. With an LED matrix manager, ADB systems can be easily implemented and LEDs in an ADB system can be dimmed individually.
Figure 6. An example of a read command.
Figure 7. The MAX25608 UART watchdog function (Channel 1: UART receiver; Channel 2: Drain voltage; Channel 3: FLTB; Channel 4: LED current).
Fault detection and protection of LED matrix manager
Detecting if LEDs are open or shorted is vital for safety. A system with safety features reduces the impact of potential failures. Checking for open or shorted LEDs in the headlight system helps catch any issues that might occur. The LED matrix manager naturally provides protection against short circuits and open circuits. The MAX25608 keeps track of any faults related to open or short circuits. The open-LED fault is triggered when the voltage between the
www.cieonline.co.uk
individual LED switch drain node (Figure 2) and the switch source node exceeds the open threshold and is reported in the status register. As shown in Figure 3, the voltage cross switch is 4.88V, which triggers an LED open fault, when open threshold is set to 4.66V. A short LED fault is triggered when the voltage between the switch drain node and the switch source node is below the short threshold for an open switch condition and is reported in the status register. Figure 4 provides an example, whereby the voltage cross switch is 2.4V, which triggers an LED short fault when the short threshold is set to 1.4V.
Safe UART communication protocol ADI’s MAX25608 provides multidrop universal asynchronous receiver-transmitter (UART) communications between the microcontroller and up to 16 MAX25608 devices. The write and read command examples are shown in figures 5 and 6. To ensure data security, the read/write transactions are protected using a 3-bit cyclic redundancy check (CRC) on the packet. If the microcontroller transmits a data packet with an incorrect CRC, the MAX25608 does not reply and discards the attempted communication.
In the event of lost communication, the UART watchdog feature of the MAX25608 sets the switches into a preconfigured state. When a microcontroller communication line is inactive for more than the set time, the fault indicator is on, and the LEDs enter a preconfigured state if the UART watchdog is enabled. As shown in Figure 7, the UART watchdog timer is set to 500ms. After a UART receiver signal is inactive for 480ms, the LEDs are turned off since the preconfigured state is off.
Performance metrics such as thermal and EMI performance can easily be evaluated. As shown in Figure 8, the matrix manager is driven by the MAX25601 boost buck LED Continues on page 36
Components in Electronics March 2026 35
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
