ZHCSI51A May 2018 – June 2018 OPA521
PRODUCTION DATA.
8.2.2.1.3 Inductor
The inductor that is connected in series with the HV Cap is required when driving low line impedances and the HV Cap is restricted to approximately 470 nF for the reasons previously stated. In applications that operate in the CENELEC A band, the impedance of the 470-nF capacitance at 40 kHz is approximately 8.5 Ω. If the application requires the ability to drive a 2-Ω load, for example, this series impedance is restrictive. Adding the series inductor can mitigate this effect. To properly select the value of the inductance, the operating frequency range of the system must be known. A common example would be the PRIME frequency band, which is approximately 40 kHz to 90 kHz. Selecting the HV Cap and inductor to have a resonant frequency in the center of the frequency band is recommended, and results in a series inductor value of 12.8 μH and HV Cap value of 470 nF. The inductor must be sized to be capable of withstanding the maximum load current without saturation, using this Equation 3 as a guideline.
