The MAX8678 is a highly integrated chip designed to power white LEDs and deliver high-quality audio output in portable devices. It features a charge pump that can drive up to four white LEDs with a dimming range from 24mA down to 0.1mA, making it ideal for backlighting or camera flash applications. Additionally, it includes a 1.1W Class AB audio amplifier with soft-start functionality to prevent inrush current and built-in protections against open and short circuits as well as thermal shutdown.
This IC is commonly used in smartphones, camcorders, PDAs, and digital cameras due to its compact design and efficient performance. The MAX8678 comes in a 16-pin 3mm x 3mm thin OFN package, offering a small footprint while maintaining high performance.
Inside the device, you'll find an integrated charge pump, LED control and current regulation circuitry, a mono Class AB audio amplifier, and associated on/off and gain control components. The pin configuration allows for flexible use, with IN providing the supply voltage (2.7V to 5.5V), LED1–LED4 driving the LEDs, and A+ and A- handling the audio input for an 8Ω speaker. The BTL output on OUT+ and OUT- delivers up to 1.1W of continuous power at 5V.
The charge pump operates efficiently by automatically disabling when the supply voltage is sufficient to drive the LEDs, thus reducing power consumption. When the voltage is insufficient, the charge pump activates, generating a negative voltage on the NEG pin to maintain the desired LED current. This ensures stable operation under varying power conditions.
For lower currents, the MAX8678 uses PWM dimming at 1kHz to reduce flicker and improve visual comfort. The duty cycle adjusts based on the required LED current, with a minimum of 1/16 to avoid visible flickering. There’s also a low-power shutdown mode where the ENLED pin must be pulled low for 3.2ms to turn off both the charge pump and LED driver.
The serial pulse interface allows for precise control over LED brightness and audio gain. With 31 levels of pseudo-logarithmic dimming, users can adjust the LED current from 24mA to 0.1mA. Similarly, the audio amplifier gain can be adjusted from -9dB to +18dB in 3dB steps using the ENAMP pin.
The MAX8678 also includes protection mechanisms such as thermal shutdown and automatic recovery when the temperature drops below 140°C. This makes it a reliable choice for demanding consumer electronics applications.
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