## Output Impedance vs. Frequency

What is Superpower's output performance under load? Amazing! Here is a graph of Zout vs.
frequency, showing a 7mΩ maximum impedance
while delivering 100mA at 40KHz. This is measured on a typical production SPL78 with 5V out.

How do we get such amazing performance? Sorry, that's a secret. But we can tell you how we measured it—we connected a resistor between the regulator output and a sine wave voltage source, then used a spectrum analyzer to measure the variation in regulator output voltage, which ideally is zero. The difference from zero equates to the output impedance of the regulator.

#### Test conditions

_{in}=11.5V

V

_{out}=5V

DC load = 5mA

voltage at load resistor = (5V

_{DC}- 5V

_{pp})

dB measurements relative to 200mV full scale

Frequency | 50Ω load (100mA pk-pk) |

10Hz | -80dB |

100Hz | -85dB |

1KHz | -83dB |

5KHz | -74dB |

10KHz | -71dB |

20KHz | -67dB |

40KHz | -63dB |

We know the current and the voltage so the values above are used to calculate output impedance. Using the spectrum analyzer full
scale value of 0.2V_{pp}, we see the following values for output impedance vs. frequency:

Frequency | 50Ω load (100mA pk-pk) |

10Hz | 1.0mΩ |

100Hz | 0.56mΩ |

1KHz | 0.71mΩ |

5KHz | 2.0mΩ |

10KHz | 2.82mΩ |

20KHz | 4.47mΩ |

40KHz | 7.08mΩ |

Superpower Z_{out} is low and flat across the entire audio band. We dare you to find or
build a better regulator! Below is a capture of the 20KHz measurement spectrum. Note that the noise floor
is due to the spectrum analyzer, not the Superpower.

Superpower, 100mApk-pk load at 10KHz

Spectrum of Superpower driving 100mA pk-pk into 50Ω.