Auto Electronics

Maxim high-brightness LED drivers save space and cost

Maxim Integrated Products has introduced two high-brightness light-emitting diode (HB-LED) driver integrated circuits for automotive applications, the MAX16819/MAX16820 and the MAX16823.

The MAX16819/MAX16820 need only one external MOSFET and a few passive components to power LEDs requiring up to 3 A of current. They can deliver from 1 W to more than 25 W of output power with up to 94% efficiency while driving as many as six white LEDs connected in series. Packaged in a lead-free, 3 mm x 3 mm, 6-pin TDFN package with exposed pad and specified for the -40 °C to 125 °C automotive temperature range, the devices are among the smallest LED drivers available with such a wide power range.

A high-voltage current-sense amplifier and up to 2 MHz switching frequency further reduce space and component-count requirements. The devices are said to minimize power dissipation, increase reliability, and reduce manufacturing costs when used for light sources such as the LED MR16 (an alternative to the traditional halogen MR16) and front and rear automotive lighting (RCL, DRL, and fog/low-beam lights).

Unlike the general-purpose buck controllers often used to power HB LEDs, the MAX16819/MAX16820 LED drivers provide high-side current sensing and employ hysteretic control. Hysteretic control is designed to ensure rapid transient response and turn-on/-off times during PWM dimming, and to provide a wide dimming range (up to 5000:1). It also supports the ability to dim at very high switching frequencies (up to20 kHz) using a dedicated DIM input, and it offers a high level of input-supply rejection as well as rapid response during LED dimming. There is no control-loop compensation, which simplifies the design and further minimizes component count.

The MAX16819/MAX16820 reduce power dissipation thanks to a voltage drop of just 200 mV across the external sense resistor. High-side current sensing and integrated current-setting circuitry minimize the number of external components while delivering an LED current with ±5% accuracy. The MAX16819 and MAX16820 offer 30% and 10% LED current ripple, respectively, without the use of an output capacitor.

A wide input-voltage range (4.5 V to 28 V) allows the MAX16819/MAX16820 to be optimized for different input-voltage standards in architectural and ambient lighting, and ensures cold-start and load dump compliance in automotive applications.

The MAX16823 is a high-voltage, three-channel, linear high-brightness LED driver with open-LED detection for automotive exterior and interior lighting applications including rear combination lamps (RCLs), center high-mounted stop lamps (CHMSL), warning lights, and RGB ambient lighting. Specified for -40 °C to 125 °C operation, it is available in a lead-free, 16-pin, TQFN (MAX16823ATE+) or TSSOP (MAX16823AUE+) package with exposed pad.

The MAX16823 operates from a 5.5 V to 40 V input-voltage range, ensuring cold-start and load-dump (up to 45 V) compliance. It delivers up to 70 mA per channel to one or more strings of HB LEDs, and operation above 70 mA is possible with the addition of an inexpensive external bipolar-junction transistor (BJT). The MAX16823also features an active-high, open-drain LEDGOOD output for open-LED detection.

The current for each of the MAX16823's channels is programmable using an external current-sense resistor in series with LEDs, thus different LED current levels can be set independently for each string when required. An internal reference provides ±5% LED current accuracy over the entire voltage and temperature operating ranges. Three dimming inputs allow for a wide range of independent PWM dimming, as well as on/off output-enable control.

Maxim said wave-shaping circuitry in the MAX16823 minimizes EMI during low-frequency PWM dimming while providing fast turn-on and turn-off times. A very low-dropout voltage (0.7 V, max) in each channel makes design easier for low-input-voltage values or for a long string of LEDs connected in series. An onboard, 3.4 V voltage regulator is capable of supplying up to 4 mA to external circuitry. The MAX16823 features output short-circuit and overtemperature protection as well as undervoltage lockout.

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