LM4910 belonging to the Boomer series of National Semiconductors is an integrated stereo amplifier primarily intended for stereo headphone applications. The IC can be operated from 3.3V ans its can deliver 0.35mW output power into a 32 ohm load. The LM4910 has very low distortion ( less than 1%) and the shutdown current is less than 1uA. This low shut down current makes it suitable for battery operated applications. The IC is so designed that there is no need of the output coupling capacitors, half supply by-pass capacitors and bootstrap capacitors. Other features of the IC are turn ON/OFF click elimination, externally programmable gain etc.
Circuit diagram of the LM4910 stereo headphone amplifier is shown above.C1 and C2 are the input DC decoupling capacitors for the left and right input channels. R1 and R2 are the respective input resistors. R3 is the feed back resistor for left channel while R4 is the feed back resistor for the right channel. C3 is the power supply filter capacitor. The feedback resistors also sets the closed loop gain in conjunction with the corresponding input resistors.
- The IC is available only in SMD packages and care must be taken while soldering.
- The circuit can be powered from anything between 2.2V to 5V DC.
- The load can be a 32 ohm headphone.
- Absolute maximum supply voltage is 6V and anything above it will destroy the IC.
- A logic low voltage at the shutdown pins shut downs the IC and a logic high voltage at the same pin activates the IC.