New Automotive Monolithic LED Driver that Ensures Stable Lighting Even During Battery Voltage Drops

Contributes to the miniaturization of the latest socket-type LED Lamps.

ROHM recently announced the development of an ultra-compact high output linear LED driver IC (BD18336NUF-M) that provides stable lighting even in the event of battery voltage drops on a single chip, 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.

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 functions by combining numerous electronic components on a modular substrate, and in recent years there is a growing demand for improved maintainability in addition to design. 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 socket size, reducing design flexibility.

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

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

Conventional products, when configured without external circuitry, can cause the LED lamps to turn OFF when the battery voltage drops, possibly creating an unsafe situation during vehicle operation. However, ROHM’s new LED driver IC delivers stable lighting while contributing to the greater miniaturization of socket LED lamps. A function for suppressing LED heat generation is also 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 current bypass function that enables stable lighting during battery voltage drops. The following features (1-1, 1-2) contribute not only to stable lighting, but greater miniaturization as well in the latest socket-type LED lamps.

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

In contrast, ROHM's new IC includes a current bypass function at voltage drops that makes it possible to smoothly switch the LED lighting path through which current flows from 3 lamps to 2 without flickering when the supply voltage from the vehicle battery drops to 9V, contributing to stable lighting that prevents LED turn OFF while maintaining at least 30% brightness at all times (vs the normal ratio). 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.

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