As with our TFT bias application, with LED drivers, there are also fault scenarios to address:
- String 1 has LED open. In this case, the fault pin will alert the MCU to this condition, and the MCU will read the I2C register to know which LED string has an open. The MCU will then pump more current to the other strings to achieve the same brightness.
- String 2 has LED short. As with the previous scenario, the fault pin will alert the MCU to the condition, and the MCU will read the I2C register to know which LED string has the short. To save power, the LED driver will shut down the string with the short. The MCU will then pump more current to the other strings to achieve the same brightness.
- Boost output voltage is low. The fault pin again alerts the MCU, and the MCU reads the I2C register to know that the boost voltage is low. Usually, the out capacitor is short to ground, or the LED is short to ground. A front protection device such as PGATE will be open. In this scenario, only important messages like speed or engine temperature will be displayed on the dashboard.
- Fail-safe operation with open enable pin. When the enable pin is open while FEN is still high, the LED driver current falls back to the default settings. The MCU can adjust the current via I2C.
Addressing the criteria outlined by the ASIL B standard, Maxim, an established leader in automotive-grade technologies, offers a portfolio of functionally safe display technologies. The company’s display bias ICs, LED drivers, power management ICs (PMICs), and other analog components are designed to support vehicle displays that enhance and ensure safety of drivers, passengers, and pedestrians. While many TFT bias ICs on the market don’t have a communication mechanism, Maxim’s ICs have I2C built in, along with the fault pin to communicate with the host MCU. Among the TFT bias products, for instance, is the MAX20067 TFT-LCD bias IC with VCOM buffer, level shifter, and I2C interface.