White LED Charge Pump with Mono Class D Audio Amp and Dual LDO

Active: In Production.

The MAX8821 integrates a charge pump for white LEDs, an audio loudspeaker amplifier, and two low-noise LDOs controlled by an I²C control interface. The high-efficiency, adaptive-mode inverting charge pump drives up to six LEDs with constant current for uniform brightness. The LED current is controlled by an I²C interface and adjusts from 0.1mA to 25.6mA per LED into 32 pseudo-logarithmic steps. Independent voltages for each LED maximize efficiency even with large LED forward voltage (V_F) mismatch. An internal temperature derating function reduces the current above +40°C to protect the LEDs.

The high-efficiency mono Class D audio amplifier delivers up to 2W into a 4Ω speaker from a 5V input supply. The amplifier features proprietary filterless Active Emissions Limiting (AEL) technology. AEL prevents high-frequency emissions resulting from conventional Class D free-wheeling behavior in the presence of an inductive load. The amplifier offers two modulation schemes: a fixed-frequency mode (FFM) and a spread-spectrum mode (SSM) that reduce EMI-radiated emissions due to the modulation frequency. The amplifier also has robust output protection and high power-supply rejection ratio (PSRR). Click-and-pop suppression is active during power-up/down, enable/disable, and for all mode changes. The amplifier's gain is adjustable through an I²C interface, from -3dB to +24dB in 10 3dB steps. Differential inputs improve common-mode noise rejection.

The LDOs in the MAX8821 are designed for low-noise operation. Each LDO output voltage can be individually programmed by the I²C interface. Both LDO1 and LDO2 have a high 70dB PSRR rating.

The MAX8821 includes soft-start, thermal shutdown, open-circuit, and short-circuit protections, and is available in a compact 28-pin, Thin QFN, 4mm x 4mm package (0.8mm max height).

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