Maxim Offers New WLED Driver With Class D Amplifier
Maxim Integrated Products has introduced the MAX8821 – described as the only white-LED (WLED) driver to combine a highly efficient, negative charge pump with a fully differential, bridged audio amplifier and two low-noise, low-dropout (LDO) current regulators.
The LED driver features a negative architecture that is said to completely eliminate high-side, in-line switch resistance loss in 1x mode, delaying 1x to 1.5x mode transitions during battery discharge. The MAX8821 utilizes independent adaptive-mode switching for each LED to further extend battery life, even with large LED forward-voltage (VF) mismatching. Moreover, the audio amplifier accepts differential input signals, and is said to offer excellent noise immunity to improve audio reproduction. The MAX8821 is well suited for use in cell phones, smartphones, PDAs, and portable media players in which every milliamp-hour of battery life is precious and PCB space is limited.
The device drives six WLEDs with 1% accurate current matching. To maximize flexibility, the MAX8821 supports I²C dimming control with 32 pseudo-logarithmic dimming levels. Additionally, this WLED driver achieves low, 70µA quiescent current, and features an on-chip, TA derating function that reduces the current above +40°C to prevent the LEDs from burning out. The integrated, dual LDO regulators deliver over 200mA of current output with low, 45µV noise and high, 70dB PSRR for sensitive circuitry.
The MAX8821’s Class D audio amplifier delivers 2W to the speaker differentially by the use of a bridge-tied load (BTL) output stage. This is said to provide up to four times more output power than a conventional, single-ended output stage and eliminates the need for an output-coupling capacitor. At 1kHz, the MAX8821’s amplifier achieves a high 65dB PSRR. Through an I²C interface, the gain is adjustable from -3dB to +24dB in ten 3dB steps. Integrated click-and-pop suppression circuitry ensures rich, clean sound quality.
The MAX8821 is available in a tiny, 4 x 4 x 0.8mm, 28-pin TQFN package and is fully specified over the -40 to +85°C extended temperature range. Prices start at $2.55.
