Diodes Incorporated Designs Buck LED Drivers to Withstand Extreme Voltage VariationsDecember 20, 2019 by Gary Elinoff
Geared for automotive lights, the AL8843Q and AL8862Q are built to drive single LEDs and multiple LED strings with up to 97% efficiency.
Diodes Incorporated has introduced two new devices—AL8843Q and AL8862Q—that are designed to supply steady current to the LEDs they power—despite any input voltage variation caused by automotive low cranking or stop-start operation.
AL8843Q and AL8862Q. Image from Diodes Incorporated
Both of the buck LED drivers are said to feature up to 97% efficiency and can operate in an ambient environment of up to +125°C.
Key Features of AL8843Q and AL8862Q
These LED drivers integrate a power switch and a high-side output current sensing circuit. An external resistor is used to set the output current. Both units feature a switching frequency of up to 1MHz, which allows for the specification of smaller external components and in turn, may conserve weight and board space.
Both parts support full-scale dimming from 0% to 100% through a control signal at the CTRL pin. The control input can be an analog input that can range from 0.4V to 2.5V. The application of 0.3V or fewer at the CTRL pin will cause the power switch to shut off.
Alternatively, the duty cycle of an applied PWM signal can also control the dimming.
PWM dimming of AL8862Q. Image from (PDF) Diodes Incorporated
For best resolution, a PWM frequency below 500kHz should be employed. The switching frequency also affects the resolution. Diodes Incorporated advises that designers can obtain the best results with higher switching and a lower PWM frequency.
Soft start limits inrush current to the LED drivers and also eliminate overshoot at the output. The soft-start time can be adjusted by an external capacitor from the CTRL pin to ground with a larger capacitor lengthening the soft-start time. In the absence of a capacitor, the default start for both LED drivers is 0.1ms.
The units feature over-temperature protection and offer protections against opens or shorts in the LED circuit.
LED open protection of AL8843Q. Image from (PDF) Diodes Incorporated
Packaging and Compliances
The AL8843Q and AL8862Q are available in SO-8EP packages. They are qualified to AEC-Q100 Grade 1, manufactured in IATF16949 certified-facilities, and support PPAP documents. They are both lead-free, halogen- and antimony- free, and are RoHS compliant.
Unique Features of the AL8843Q
The (PDF) AL8843Q can work with input voltages ranging from 4.5V to 40V. With an integrated 40V/0.2Ω power MOSFET, this LED driver can supply up to 3A with a total output power of up to 30W possible.
A typical application circuit for the AL8843Q. Image from (PDF) Diodes Incorporated
The quiescent current is 0.35mA.
Unique Features of the AL8862Q
The (PDF) AL8862Q can work with input voltages ranging from 4.5V to 55V. This unit features an internal 60V/0.4Ω power MOSFET to support 1A LED current.
Functional block diagram of the AL8862Q. Image from (PDF) Diodes Incorporated
The quiescent current is 0.45mA.
The AL8862Q is more suited to automotive interior niches due to its somewhat low-power output. The higher-powered AL8843Q will find applications in:
- Fog lights
- Brake/stop signals
- Daytime running lights
- Turn lights
Around the Industry
ST’s A5975D is a step-down switching regulator for automotive applications that can provide up to 3A. The device supports an output voltage range from 1.235V to 35V.
The TPS92520-Q1 from TI is a monolithic buck LED driver with a 4.5V to 65V input range that can independently power two strings of series-connected LEDs.