A method comprising: providing from a charge pump power supply a power supply voltage to a power supply input of a power amplifier (A1) having an audio input configured to receive an audio input signal, and an audio output configured to generate an analog audio signal (V OUT ) for playback at a transducer device having a load impedance (R L ) and configured to be coupled to the audio output via an electrical terminal ; the method further comprising: detecting a peak amplitude (V ripple ) of a voltage ripple of the power supply voltage (V SUPPLY ) in response to a transition of the analog audio output signal (V OUT ); detecting a peak amplitude (V pk ) of a change in a digital audio input signal (DIG_IN) that causes the transition of the analog audio output signal (V OUT ), wherein the digital audio input is input to a digital-to-analog conversion circuit coupled to the power amplifier (A1) and configured to convert a digital audio input signal (DIG_IN) into the analog audio input signal; and estimating a value of the load impedance (R L ) using the relationship V ripple =V pk R switch /R L , wherein V ripple is the peak amplitude of the voltage ripple, V pk is the peak amplitude of the change in the digital audio input signal, and R switch is an input series resistance of the the charge pump power supply . providing from a charge pump power supply a power supply voltage to a power supply input of a power amplifier (A1) having an audio input configured to receive an audio input signal, and an audio output configured to generate an analog audio signal (V OUT ) for playback at a transducer device having a load impedance (R L ) and configured to be coupled to the audio output via an electrical terminal ; the method further comprising: detecting a peak amplitude (V ripple ) of a voltage ripple of the power supply voltage (V SUPPLY ) in response to a transition of the analog audio output signal (V OUT ); detecting a peak amplitude (V pk ) of a change in a digital audio input signal (DIG_IN) that causes the transition of the analog audio output signal (V OUT ), wherein the digital audio input is input to a digital-to-analog conversion circuit coupled to the power amplifier (A1) and configured to convert a digital audio input signal (DIG_IN) into the analog audio input signal; and estimating a value of the load impedance (R L ) using the relationship V ripple =V pk R switch /R L , wherein V ripple is the peak amplitude of the voltage ripple, V pk is the peak amplitude of the change in the digital audio input signal, and R switch is an input series resistance of the the charge pump power supply . detecting a peak amplitude (V ripple ) of a voltage ripple of the power supply voltage (V SUPPLY ) in response to a transition of the analog audio output signal (V OUT ); detecting a peak amplitude (V pk ) of a change in a digital audio input signal (DIG_IN) that causes the transition of the analog audio output signal (V OUT ), wherein the digital audio input is input to a digital-to-analog conversion circuit coupled to the power amplifier (A1) and configured to convert a digital audio input signal (DIG_IN) into the analog audio input signal; and estimating a value of the load impedance (R L ) using the relationship V ripple =V pk R switch /R L , wherein V ripple is the peak amplitude of the voltage ripple, V pk is the peak amplitude of the change in the digital audio input signal, and R switch is an input series resistance of the the charge pump power supply . <EOS>