7.3.2.2 Headphone Outputs

The stereo headphone drivers on pins HPL and HPR can drive loads with impedances down to 16Ω in single-ended AC-coupled headphone configurations, or loads down to 32Ω in differential mode, where a speaker is connected between HPL and HPR. In single-ended drive configuration these drivers can drive up to 15mW power into each headphone channel while operating from 1.8V analog supplies. While running from the AVdd supply, the output common-mode of the headphone driver is set by the common-mode setting of analog inputs to allow maximum utilization of the analog supply range while simultaneously providing a higher output-voltage swing. In cases when higher output-voltage swing is required, the headphone amplifiers can run directly from the higher supply voltage on LDOIN input (up to 3.6V). To use the higher supply voltage for higher output signal swing, the output common-mode can be adjusted to either 1.25V, 1.5V or 1.65V. When the common-mode voltage is configured at 1.65V and LDOIN supply is 3.3V, the headphones can each deliver up to 40mW power into a 16Ω load.

The headphone drivers are capable of driving a mixed combination of DAC signal and bypass from analog input INL and INR. The analog input signals can be attenuated up to 72dB before routing. The level of the DAC signal can be controlled using the digital volume control of the DAC. To control the output-voltage swing of headphone drivers, the digital volume control provides a range of –6.0dB to +29.0dB ⁽¹⁾ in steps of 1dB. These level controls are not meant to be used as dynamic volume control, but more to set output levels during initial device configuration. Refer to for recommendations for using headphone volume control for achieving 0dB gain through the DAC channel with various configurations.