New devices for automotive lighting applications

18 November 2014

ON Semiconductor introduced two devices for use in vehicle lighting systems at electronica 2014.

Solutions enable engineers to support a more versatile ‘platform’ approach that minimises implementation costs.

The NCV78763 advanced smart power ballast and dual channel LED driver provides a highly efficient single-chip automotive lighting solution that is capable of driving two strings of LEDs up to 60V. A DC current of 1.6A can be supported on each output and the built-in current-mode voltage booster controller enables input current filtering. An internal pulse-width modulated (PWM) dimming function, covering frequencies up to 4kHz is also included in addition to the option of PWM direct-feed for full frequency and resolution control from the external microcontroller. Optimised for front lighting applications, this device can be employed in high beam, low beam, turn indicator, static cornering, fog and daytime running lights. 

For each individual LED channel there is an independent buck switch output, through which both the output current and voltage can be configured to meet specific application criteria. Configuration is done via the device’s serial peripheral interface (SPI). Integrated diagnostic features mean that less of the system microcontroller’s resources need to be devoted to safety monitoring, thereby improving overall effectiveness of the lighting design. If more than two LED channels are required on one lighting module, then multiple NCV78763 devices can be combined together. 

Due to the SPI programmability, this solution is highly flexible - permitting the scaling up of designs so that more LED strings can be utilised. This results in multiple system configurations which are able to address an expansive range of automobile models, with significantly faster design cycles and lower engineering overheads. Furthermore, the NCV78763 supports high operating frequencies and thus permits specification of smaller inductors, reducing bill of materials costs.

Also introduced at electronica was the NCV7691 current controller for automotive LED lamps. Targeted predominantly at automotive rear combination lamps (RCL), centre high-mounted stop lamps (CHMSL), and day-time running lights (DRL), this highly integrated pre-driver contains PWM and diagnostic capabilities, as well as battery connection and negative temperature coefficient (NTC) input in a single chip. 

Through use of external bipolar transistor(s) combined with feedback resistors, this device accurately regulates the LED driver current - with up to eight LED strings being driven concurrently. Engineers have the flexibility to add channels to create multi-channel systems. A dedicated dimming feature is included via the PWM input pin. LED brightness levels can be programmed in a straightforward manner using an external resistor in series with the bipolar transistor. This approach gives engineers the ability to use this device over a wide range of currents. Set back power limit reduces the drive current during over-voltage conditions. Open LED string and short-circuit diagnostic functions ensure that operational reliability is maintained. By connecting the FLTS pins together, multiple devices can be turned off in case of a detected error.  AEC-Q100 qualified, the NCV7691 can deal with harsh automotive environments. It has a -55 to +150 °C operational temperature range.  

Packaging and Pricing

The NCV78763 is offered in three package variants: 5 x 5 mm QFN-32, 7 x 7 mm QFN-32 and 36-pin SSOP, with unit prices starting at $1.85 USD for 5K unit quantities.  The NCV7691 is available in an SOIC-8 package with unit pricing at $0.29 USD in 3K unit quantities.

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