HB LED drivers deliver 94 percent efficiency

These devices require just one external MOSFET and only a few passive components to power LEDs that need up to 3A of current. Each is capable of delivering from 1W to over 25W of output power with up to 94 percent efficiency, while driving as many as six white LEDs connected in series.

Smallest` package
Packaged in a tiny 3-by-3mm TDFN, these devices are said to be the smallest LED drivers to provide LED-driver designs with such a wide power range. Moreover, a high-voltage current-sense amplifier and up to 2MHz switching frequency further reduce space and component-count requirements. These highly integrated devices minimize power dissipation, increase reliability and reduce manufacturing costs, making them suitable for light sources such as the energy-efficient 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 most commonly used to power HB LEDs, the MAX16819/MAX16820 LED drivers employ hysteretic control. With this control technique, the drivers ensure rapid transient response and turn-on/-off times during PWM dimming, which translates into a wide dimming range (up to 5000:1) or the ability to dim at very high switching frequencies (up to 20kHz) using a dedicated DIM input. Hysteretic control also 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.

High-side current sensing
High-side current sensing further differentiates these drivers from standard buck PWM controllers. Because the voltage drop across the external sense resistor is only 200mV, the MAX16819/MAX16820 reduce power dissipation. In addition, the high-side current sensing and integrated current-setting circuitry minimize the number of external components while delivering an LED current with ±5 percent accuracy. The MAX16819 and MAX16820 offer 30 percent and 10 percent LED current ripple, respectively, without the use of an output capacitor.

A wide input-voltage range (4.5V to 28V) 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. These LED drivers are specified for the automotive temperature range (-40°C to 125°C) and are available in a Pb-free, 3-by-3mm, 6-pin TDFN package with exposed pad. Prices start at 58 cents (1,000-up, FOB USA). 

Specifications:

• High-Side Current Sense
• Dedicated Dimming Control Input
• 20kHz Maximum Dimming Efficiency
• Hysteretic Control: No Compensation
• Up to 2MHz Switching Frequency
• ±5% LED Current Accuracy
• Adjustable Constant LED Current
• 4.5V to 28V Input Voltage Range
• Over 25W Output Power
• 5V, 10mA On-Board Regulator
• -40°C to +125°C Operating Temperature Range