LED headlight driver has main-dip switching

LED headlight driver has main-dip switching

LED headlight driver has main-dip switching

A80803 is a boost and buck-boost dc-dc converter for headlights, that includes switching for high-beam and dip-beam strings.

It works with inputs over 5 to 37 V (40V abs max for load dump, 4.5V under-voltage lock-out). Output can be up to 70V

Drivers are included for external high and low-side dc-dc mosfets and a mosfet each for main and dip beam (above diagram).

Control can be over an SPI bus, or factory-programmed and stored in EEPROM to eliminate the need for a host MCU – if external circuitry is required, a 5V 50mA regulated output is provided. Diagnostics can be reported through SPI or via the two fault pins.

Topology is fixed frequency (with optional dithering for EMC mitigation) peak current mode control.

Dimming is through a PWM signal on the enable pin or by an internal PWM signal configured via SPI.

LED headlight driver has main-dip switching

A80804 is a linear driver for four independent strings, intended for day-time running light, position lights and stop-tail lights, as well as “sequential turn signals, animation effects and theater-style transitions,” said Allegro. With no dc-dc converter, the “low EMI output helps it achieve CISPR25 Class 5 compliance”.

Input voltage range is 5.3 to 40V.

Dimming is through internal or external PWM (one input per string), with internal PWM set by Resistor divider or analogue voltage. If multiple devices are used to add LEDs, a PWM output us available to feed the dimming inputs of the additional ICs.

“All channels can be dimmed with internal PWM dimming and automatic phase shifting,” according to the company. “The overall LED current can be switched between low and full intensity for applications including stop-tail or DRL-position lighting. Multiple analogue dimming options are available to support LED binning or NTC [thermistor] fold-back. Selectable LED current slew-rate control is available to tune PWM edge times and improve EMI performance.”

Fault detection includes: drain short to ground, drain short to Vin, open LED and device over-temperature.

The current sense resitor has a 500mV current-sense reference, reduced to 200 mV in the A80804-1 to save power.

All devices above are packaged in 32pin 5 x 5mm QFN with wettable flanks.

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