The **LM4919** is a ground-referenced, low-voltage, audio power amplifier primarily designed for stereo headphones in portable applications. It belongs to Texas Instruments' *Boomer* series. --- ## 1. Key Specifications The LM4919 is known for its ability to operate without bulky output coupling capacitors, saving significant PCB space. | Parameter | Value / Range | | :--- | :--- | | **Operating Voltage** | 2.2V to 5.5V | | **Output Power** | 85mW (per channel) into 32Ω at 3V | | **THD+N** | 1.0% (typical) | | **Quiescent Current** | 1.1mA (typical) | | **Shutdown Current** | 0.02µA (typical) | | **PSRR** | 65dB at 217Hz | --- ## 2. Main Features & Components To understand the electronic parts of an LM4919 circuit, we must look at its internal architecture and required external components. ### Internal Architecture * **Dual Amplifiers:** It contains two independent operational amplifiers for stereo (Left/Right) audio. * **Charge Pump:** This is the "secret sauce." It generates a negative voltage rail internally. This allows the audio signal to swing around 0V (Ground), eliminating the need for DC-blocking capacitors at the output. * **Shutdown Control:** An active-low pin that disables the device to conserve battery life. ### Required External Components | Component | Function | | :--- | :--- | | **Input Capacitors ($C_i$)** | Blocks DC offset from the audio source while allowing AC signals to pass. | | **Input Resistors ($R_i$)** | Sets the input impedance and works with $R_f$ to define gain. | | **Feedback Resistors ($R_f$)** | Determines the closed-loop gain of the amplifier ($Gain = -R_f / R_i$). | | **Bypass Capacitor ($C_{fly}$)** | Used for the internal charge pump to generate the negative rail. | | **Tank Capacitor ($C_{pvss}$)** | Stabilizes the generated negative voltage supply. | --- ## 3. Typical Application Circuit The circuit is straightforward because it avoids large electrolytic capacitors on the output lines. ```text Input L ---[ Ci ]---[ Ri ]---+---( -In L ) | [ Rf ] | Output L <-------------------+---( Vo L ) (Similar structure for Right Channel) ``` ### Advantages of the OCL (Output Cap-Less) Design: 1. **Improved Low-Frequency Response:** Since there is no output capacitor to form a high-pass filter, the bass response is much better. 2. **Size Reduction:** Eliminates two large 100µF–220µF capacitors usually required in headphone amps. 3. **Cost:** Lower bill of materials (BOM) cost. --- ## 4. Pin Configuration (10-Pin VSSOP/WSON) | Pin No. | Name | Description | | :--- | :--- | :--- | | 1 | SHUTDOWN | Logic low to disable the chip | | 2 | C1P | Charge Pump Flying Cap Positive | | 3 | C1N | Charge Pump Flying Cap Negative | | 4 | VSS | Negative Supply (generated internally) | | 5, 8 | -IN | Inverting Inputs for Left/Right | | 6, 7 | Vo | Audio Outputs for Left/Right | | 9 | VDD | Positive Power Supply | | 10 | GND | System Ground |