8.3.4 PLIMIT Operation

The TPA3126D2 has a built-in voltage limiter that can be used to limit the output voltage level below the supply rail. The amplifier operates as if it was powered by a lower supply voltage, and thereby, limits the output power. Add a resistor divider from GVDD to ground to set the voltage at the PLIMIT pin. An external reference may also be used if tighter tolerance is required. Add a 1-µF capacitor from pin PLIMIT to ground to ensure stability.

Figure 27. Power Limit Example

The PLIMIT circuit sets a limit on the output peak-to-peak voltage. This is done by limiting the duty cycle to a fixed maximum value. The limit can be considered as a "virtual" voltage rail which is lower than the supply connected to PVCC. The "virtual" rail is approximately four times the voltage at the PLIMIT pin. The output voltage can be used to calculate the maximum output power for a given maximum input voltage and speaker impedance.

Equation 2.

where

• P_OUT (10%THD) = 1.25 × P_OUT (unclipped)
• R_L is the load resistance.
• R_S is the total series resistance including R_DS(on), and output filter resistance.
• V_P is the peak amplitude, which is limited by the "virtual" voltage rail.