“In the Asian region, where 2-wheeled vehicles are the main means of transportation for many, a number of vehicle manufacturers are demanding simpler circuit configurations for driving standard rear and license plate lamps,” according to Rohm. “However, until now thermal design issues have made it difficult for LED drivers that power LEDs to meet all of the various requirements in terms of number of lamps, brightness, safety, and costs.”
Having analysed the largest market for two-wheeled vehicles, India, the company decided on four channel drivers producing 150mA/channel, with per-channel current adjustment, in a 16pin package.
The result was:
BD18337EFV-M for driving three-high series strings of LEDs
BD18347EFV-M for driving two-high series strings of LEDs.
The chip comes in a 5x6mm gull-wing package with a thermal pad underneath.
Internal constant current regulators are included and, to ease heat dissipation at high current, it is possible to put a resistor in series with each LED strong to help share the voltage drop between power rail and string tops. Also however, Rohm has provided a separate pin (VinRes) and an internal control circuit to allow all these resistors to be combined into one for certain combinations of rail, LED count and current.
Fault detection and protection includes: LED open, short-circuit, over-voltage and temperature. When multiple instances of this chip are used to control light on the same vehicle, a one-pin bus between the chips allows fault status to be shared and acted on.
“If a rear lamp fails to light up, designers can select to turn all of the lamps off or only the failed string,” said Rohm. “Given that the safety standards for two-wheeled license plate lights in the event of abnormalities vary from country to country, this latest series enables compliance with multi-regional laws with a single setting.”
Applications are expected in: rear lamps (stop/tail), fog lamps, turn signal indicators, number plate lamps and daytime running lights.
| Part No. | Function | Channels | Supply | Withstand | Max. Output | Current accuracy | Operating range | Package |
|---|---|---|---|---|---|---|---|---|
| BD18337EFV-M | 3-stage LED driver | 4 | 5.5V to 20.0V | 40V | 150mA/ch (500mA total) |
±5% | -40 to 125ºC | HTSSOP-B16 |
| BD18347EFV-M | 2-stage LED driver* |
There is a lot to these chips, revealed by the data sheet.