10.4.3 Thermal Performance with Non-Continuous Output Power

As audio signals often have a peak to average ratio larger than one (average level below maximum peak output), the thermal performance for audio signals can be illustrated using burst signals with different burst ratios.

Figure 34. Example of audio signal

A burst signal is characterized by the high-level to low-level ratio as well as the duration of the high level and low level, e.g. a burst 1:4 stimuli is a single period of high level followed by 4 cycles of low level.

Figure 35. Example of 1:4 Burst Signal

The following analysis of thermal performance for TPA3255-Q1 is made with the heatsink temperature controlled to 75°C.

The device is not thermally limited with 8-Ω load, but depending on the burst stimuli for operation at 75ºC heatsink temperature some thermal limitations may occur with a lower load impedance, depending on switching frequency and average to maximum power ratio. The figure below shows burst performance with a signal power ratio of 1:16 (low cycles power level 1/16 of the high cycles power level) and 1:8 .

Figure 36. Maximum Burst Output Power vs Frequency, BTL, 4Ω Load, Each Channel, T_C = 75°C, Power Ratio 1:16

Figure 37. Maximum Burst Output Power vs Frequency, BTL, 4Ω Load, Each Channel, T_C = 75°C, Power Ratio 1:8