This week, Diodes Incorporated the AL3353, an LED/LCD boost controller.
Diodes Inc. intends for the new controller to be suitable for applications where a constant voltage or constant current are required to drive displays and backlights. On the LCD side, this may include use as a backlight driver for LCD TVs, LCD monitors, and flat panel displays. On the LED side, that may mean use as an LED driver for commercial lighting applications.
The AL3353 LED/LCD boost controller. Image from Diodes Incorporated
The device accommodates input voltages ranging from 9V to 40V. This allows it to easily adapt to a variety of common supply voltages, such as 12V, 24V, and 36V, without further configuration or loss of efficiency.
Pulse Width Modulation for Control
The dimming level is controlled by a digital PWM (pulse width modulation) input, which is converted to an analog voltage to effect control of the actual dimming. The AL3353 can support PWM signals with frequencies ranging from 5kHz to 50kHz.
Additionally, the AL3353 maintains linearity across temperature and process variations. This is accomplished through the implementation of Diodes’ dynamic linearity compensation technique, which uses an offset cancellation chopping circuit.
Constant Current Control
The AL3353 contains a PWM boost driver that uses current mode control and fixed frequency operation to regulate the LED current. The LED current passes through an external current sense resistor. The voltage across the sensing resistor is then compared with a reference level of 400mV. The difference between the two voltages is used to control the pulse width of the power switch, and allowing for regulation of the current flowing through the LED.
The AL3353 in a constant current application. Image from the Diodes Incorporated product announcement
Constant Voltage Control
The AL3353 can also be used in situations requiring output voltage control, rather than output current control. It does so by making measurements with a feedback resistor network connected to the device’s output terminal.
The AL3353 in a constant voltage application. Image from Diodes Incorporated
To protect itself and the LEDs it controls, the AL3353 incorporates some important safety features. These include:
- Undervoltage lockout (UVLO)
- Output overvoltage protection (OVP)
- Power MOSFET overcurrent protection (OCP)
- Diode and inductor short protection
- LED cathode short to GND protection
- LED open protection
- VOUT short protection
- Overtemperature protection (OTP)
The AL3353 is available in the SO-8 (type TH2) package.
The AL3353 can replace many discrete components and could reduce BOM costs, as well as reducing board space with its relatively small size:
SO-8 Type TH2 package size information. Image from the datasheet.
Given this part's utility, it's no wonder that there are other entrants into this field. And, while the AL3353 provides one output, some manufacturers offer parts with up to four outputs. Here are a few:
- The MP3385A from Monolithic Power works from an input voltage supply ranging from 4.5V-to-33V. In addition to PWM control, it can also work from analog control signals, and also from combined analog and PWM dimming modes to meet different application requirements. It can provide output voltages of up to 80 volts.
- The ADD5211 from Analog Devices is a four-string, white LED Driver for LCD backlight applications. The unit employs a PWM boost controller to generate the minimum output voltage required to drive the LED string at the programmed LED current. It operates from input voltages ranging from 4.5 V to 40 V.