A scenario may also occur when connecting a low frequency LC filter (<< switching frequency of the Class-D amplifier output) at the Class-D output since this generates a ripple current which propagates through the Class-D FETs. In such a scenario the AVDD Y-bridge may also have to be disabled or the AVDD Y-bridge threshold may need to be reduced, depending on the amount of ripple current through the LC filter to avoid triggering an AVDD Y-bridge Over current error.

To avoid OC errors, it must be ensured that peak audio current + Ripple current through the LC filter < AVDD Bridge Over current threshold. Assuming that the amplifier was switching on PVDD bridge,

The ripple current through the LC filter for TAS2572 can be calculated as:

• ΔI= PVDD/(4*L*Fsw) (Operating in PVDD bridge)

Where PVDD= PVDD supply voltage, L= Inductor value & Fsw= switching frequency of the Class-D amplifier.

For example, if the L=1uH & C=0.68uF and Fsw=384KHz, PVDD=13V the ripple current is ±0.84A, when the Class-D switches from PVDD rail into AVDD bridge, which will trigger the Over current error, irrespective of AVDD Y-bridge threshold. This forces the AVDD bridge to be disabled always.

However, if the Boost voltage is sufficiently low <9V, it may be possible to still utilize the AVDD Y-bridge to save efficiency at low power levels. Alternatively, the user can increase the Inductance value & reduce the capacitance to still achieve the same LC filter cutoff frequency and mitigate the high ripple current (at the cost of BOM size & cost for the inductor).

Figure 2-7 Image showing the Class-D output ripple current with LC filter