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Home > News > Industry News > Simple constant current LED dr.....

Simple constant current LED drivers for automotive

  • Author:Ella Cai
  • Release on:2018-07-27
Diodes has released simple LED driving chips for regulating current in strings of LEDs, particularly in cars and other road vehicles – some of which match parts from Infineon and Nexperia (see table below).

Called the the BCR4xxUW6Q series, they come in SOT26 (SC70) packages and are expected to find use with LEDs displacing conventional bulbs throughout the car: from external lighting such as side markers, puddle lighting and sill plates, to internal lighting including dome, ambient lights, instrument clusters and button back-lighting.

For low-profile applications, the related BCR4xxUFDQ series comes in 0.6mm high DFN2020-6 packages. “The thinner DFN2020 is designed for edge-lighting applications in which a less intrusive, lower-height package is required,” said the firm.

Each devices in the series can provides a pre-set current output (see table below) without the need for any external components, or deliver more current if a resistor is added.

Max currents are:
  • 100mA – BCR401, BCR402, BCR405 
  • 200mA – BCR420 
  • 350mA – BCR421 

All have 10mA minimum current except the 402 (20mA) and 405 (50mA)

421 devices can be directly pwm dimmed by a 3.3V microcontroller – dimming to 1% is possible at 25kHz, while 420s need a 24V PWM waveform.

Diodes BCR4xxUxxQ401, 402 and 405 are pnp-based high-side devices that need an open collector or open drain drive for PWM dimming.

With an open drain drive, turn on time is 200ns, while turn off time is much slower at 10µs, which can affect dimming linearity at 25kHz. For better dimming (see for example this data sheet) switching both the bottom of the LED string and the input resistor via an n-channel mosfet it suggested – making turn-off time around 200ns.

Infineon and Nexperia parts

All devices have a negative temperature coefficient, which lowers the LED driver current as the internal temperature rises, “thereby protecting and extending the lifetime of the LEDs”, claimed the firm.

Maximum voltage is 40V, and maximum total power dissipation is 1.7W for the DFN2020s and 1W for the SOT-26 parts.