LED Driver IC that Ensures Stable Lighting During Battery Voltage Drops

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  • ROHM’S latest development, the BD18336NUF-M maintains 30 per cent brightness at all times
  • Use of fewer components enables designing of ultra-compact LED lamps

Automotive lamps are increasingly adopting LEDs due to their longer life and high-density mounting. Conventional onboard LEDs support various designs and functions by combining numerous electronic components on a modular substrate. Also, socket-type LED lamps that can be replaced as easily as LED bulbs have been attracting attention by offering superior maintainability. However, it is difficult to decrease the socket size for better design flexibility.

In response, ROHM has developed a new, compact and high output linear LED driver IC, BD18336NUF-M  that enables mounting in ultra-compact socket-type LED lamp circuits while ensuring stable lighting even during drop in battery voltage, making it ideal for a broad range of socket-type LED lamps used in vehicle systems, from DRLs (Daytime Running Lamps) and position lighting to rear lamps.

Maintains stable lighting during battery voltage drops

Vehicle batteries normally supply a voltage of 13V (12V considering the backflow protection diode), but the output can vary due to various factors. With conventional products, when the voltage drops to as low as 9V, unless an external circuit is configured, the LEDs may turn OFF, which can cause problems by creating an unsafe situation when driving.

The BD18336NUF-M has a current bypass function that prevents LED turn OFF.  A smooth switching of the LED lighting path occurs through which current flows from 3 lamps to 2 without flickering when the supply voltage from the vehicle battery drops to 9V and maintains 30 per cent brightness at all times. This function can be configured using 3 external resistors (for the operating start voltage and operating interval), providing greater flexibility for a wide range of applications.

Reduced mounting area for supporting ultra-compact socket-type LED lamps

The built-in current bypass function ensures stability during battery voltage drops that make it possible to decrease mounting area by up to 30 per cent (including external circuitry). While conventional products may cause the LEDs to blink if configured without external circuitry (comprised of comparators, transistors, and other components) when the battery voltage drops, ROHM’s new IC makes it easy for stable lighting up of LEDs. This enables mounting on 10mm square LED module substrates, allowing the configuration of ultra-compact LED lamps that could not be achieved in the past.

Compatible with various lamp colours, including high brightness white LEDs

Conventional products are not suitable for driving white LEDs which are prone to high temperatures that reduce LED life. Therefore, the BD18336NUF-M enables adjustment of the output current and supports various colours. It includes an output current derating function that limits the amount of heat generated by reducing the output of the LED driver when the temperature of the LEDs becomes too high. This function is designed for ultra-compact socket LED lamps while allowing the output current with respect to temperature to be adjusted by a single external thermistor. Thus, it is suitable for a wide range of automotive lamp systems, including DRLs that use white LEDs along with rear and position lamps requiring red and yellow LEDs.

Other electrical characteristics

  • Input voltage range: 5.5V to 20.0V
  • Rated voltage: 42V
  • Max. output current: 400mA (DC); 600mA (Duty 50 per cent)
  • Operating temperature range: – 40 degrees Celsius to + 150 degrees Celsius

Sample availability of the IC has begun and OEM quantities will be available from July 2020.


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