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New Automotive Monolithic LED driver for Stable Lighting

ROHM recently announced the introduction of an ultra-compact high output linear LED driver IC (BD18336NUF-M) that gives stable lighting even in the event of battery voltage drops on one chip, which makes it well suited for a broad selection of socket-type LED lamps used in vehicle systems, from DRLs (Daytime Running Lamps) and position lighting to rear lamps.

In the automotive market, vehicle lamps are increasingly adopting LEDs due to their longer life and high-density mounting. Conventional onboard LEDs support various designs and processes by combining numerous electronic components on the modular substrate, as well as in the past few years there's a growing interest in improved maintainability in addition to design. Socket-type LED lamps that may be replaced as easily as LED bulbs happen to be attracting attention by providing superior maintainability. However, it is difficult to decrease socket size, reducing design flexibility.

In response, ROHM developed a new LED driver IC that allows mounting in ultra-compact socket-type LED lamp circuits while ensuring stable lighting even during stop by battery voltage.

The BD18336NUF-M adopts a present bypass function that prevents LED turn OFF and keeps a brightness of at least 30% all the time by switching the LED current path, even when battery voltage decreases from 13V to 9V. In addition, a high creation of 600mA is achieved in an ultra-compact 3.0mm square package, and mounting area is reduced by approx. 30% over conventional solutions (such as the external circuit), making mounting possible on the 10mm square substrates necessary for small socket-type LED lamp

Conventional products, when configured without external circuitry, may cause the LED lamps to show OFF when the battery voltage drops, possibly creating a hazardous situation during vehicle operation. However, ROHM's new LED driver IC delivers stable lighting while contributing to the higher miniaturization of socket LED lamps. A function for suppressing LED heat generation can also be built in that supports white LEDs that typically run hot, allowing them to be used in DRLs and other vehicle lighting systems utilizing white LEDs.

Key Features

  1. Monolithic design ensures stable lighting during battery voltage drops

The BD18336NUF-M is the first single-chip (ultra-compact 3.0mm square package) IC to incorporate a present bypass function that enables stable lighting during battery voltage drops. The next features (1-1, 1-2) contribute not just to stable lighting, but greater miniaturization as well in the latest socket-type LED lamps.

1-1. Maintains at least 30% brightness all the time even when the automobile battery voltage decreases to 9V

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

In contrast, ROHM’s new IC features a current bypass function at voltage drops which makes it easy to smoothly switch the LED lighting path by which current flows from three lamps to two without flickering once the supply voltage in the vehicle battery drops to 9V, adding to stable lighting that stops LED turn OFF while keeping at least 30% brightness all the time (vs the normal ratio). This function can be configured using 3 external resistors (for that operating start voltage and operating interval), providing greater flexibility for any wide range of applications.

1-2. Reduces mounting area by 30% over conventional solutions, enabling support for ultra-compact socket-type LED lamps

The built-in current bypass function ensures stable driving during battery voltage drops that cuts down on the quantity of external parts by 7 over conventional designs, to be able to decrease mounting area by as much as 30% (including external circuitry). While conventional products may cause the LEDs to blink if configured without external circuitry (made up of comparators, transistors, along with other components) when the battery voltage drops, ROHM's new IC makes it easy to stably illuminate LEDs with a single chip. This permits mounting on 10mm square LED module substrates, allowing the configuration of ultra-compact LED lamps that may not be achieved in the past.

  1. Suitable for various lamp colors, including high brightness white LEDs

The BD18336NUF-M includes an output current derating function that limits the quantity of heat generated by reducing the creation of the LED driver once the temperature of the LEDs becomes too high. This function is designed for ultra-compact socket-type LED lamps while allowing the output up-to-date with respect to temperature to be adjusted by a single external thermistor.

Whereas conventional products are not suitable for driving white LEDs that are vulnerable to high temperatures in the viewpoint of LED life, ROHM's IC enables adjustment of the output current and supports various colors, making it well suited for an array of automotive lamp systems, including DRLs which use white LEDs along with rear and position lamps requiring red and yellow LEDs.

Other Electrical Characteristics

Availability: Now (samples), July 2022 (OEM quantities)

Application Examples

DRLs (Daytime Running Lamps)

Position Lamps

Rear Lamps

Fog Lamps-and other vehicle lamps