LM4890

The LM4890 is a Class AB audio power amplifier designed for demanding mobile phones and other portable communication devices. At a 5V supply voltage with a 1kHz input, it delivers a maximum output power of 1W into an 8Ω load, with total harmonic distortion plus noise less than 1% across the 20Hz to 20kHz audio band. The device features a simple application circuit requiring minimal external components to deliver high-quality output power. The LM4890's output requires no external coupling or bootstrap capacitors, making it ideal for low-voltage, low-power applications. It supports a shutdown mode for reduced power consumption and employs a switching suppression technique that effectively eliminates power-on and power-off noise. The LM4890 is unity-gain stable, and the amplifier's voltage gain can be adjusted by configuring external resistors for ease of use. The gain is given by: AvD = 2 × (Rf / Ri). The bridge output topology delivers four times the output power compared to single-ended mode under the same conditions. The maximum power dissipation is given by PDMAX = 4 × (VDD)² / (2π² RL), which must not exceed the package thermal limit calculated by PDMAX = (TJMAX - TA) / θJA, where θJA = 190 °C/W and TJMAX = 150 °C for the LM4890 surface-mount package. Proper power supply bypassing is critical for low-noise performance and supply filtering; 10μF and 0.1μF bypass capacitors should be placed as close as possible to the device's supply pins. The LM4890 features a shutdown mode and power-down capability for further power reduction, with a typical quiescent current of 0.1μA in shutdown. The SHUTDOWN pin must be properly driven by an external signal and must not be left floating.

Applications

• Mobile phones
• PDAs and tablets
• Portable devices
• Smart voice modules
• Smart learning pens

Key features

• High output power: 1W into 8Ω load at 1kHz (THD+N < 10%)
• Excellent pop-and-click suppression for power-on and power-off noise
• No bootstrap capacitor required
• Unity-gain stable
• Low shutdown leakage current, typically 0.1μA
• Wide supply voltage range: 2.2V ~ 5.5V
• Externally adjustable gain
• Available in SOP-8/MSOP-8 packages