Texas Instruments PurePath TAS5766M, User Manual

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30 PurePath™ Smart Amp User Manual (TAS5766M/68M)
A practical capacitor size will not help much with these peaks therefore it is recommended to
design the power supply based on the expected peak currents. The peak current observed at
the power supply can be approximated by calculating the maximum current into the load taking
the amplifier efficiency into account.
𝐼
𝑠𝑠 , 𝑖𝑖
=
𝑃
𝑠𝑠 , 𝑜𝑜𝑡
𝜂 × 𝑉
𝑑𝑑
× # 𝑐ℎ𝑎𝑎𝑎𝑎𝑎𝑎
The peak input current can also be calculated if the full-scale voltage is known, as shown below.
Section
5.4 covers the output levels in more detail.
𝐼
𝑠𝑠 , 𝑖𝑖
=
𝑉
𝑠𝑠 , 𝐹𝐹
2
𝜂 × 𝑉
𝑑𝑑
× 𝑍
𝐿
× # 𝑐ℎ𝑎𝑎𝑎𝑎𝑎𝑎
The table below lists several peak supply current examples. Note that these calculations assume
a resistive load. Speakers are inductive in nature and may cause higher peak currents as
discussed in Section
5.3.
Table 6. Peak Input Current Examples (One Channel)
Speaker Nominal
Impedance
𝒁
𝑳
(ohms)
Full-scale Peak
Voltage
𝑽
𝒔𝒔 , 𝑭𝑭
(V)
Efficiency
𝜼
Supply Rail
𝑽
𝒅𝒅
(V)
Supply Current
𝑰
𝒔𝒔 , 𝒊𝒊
(A)
4
3 0.92 12 0.2
6 0.92 12 0.82
12 0.92 24 1.63
18 0.92 24 3.67
8
3 0.92 12 0.1
6 0.92 12 0.41
12 0.92 24 0.82
18 0.92 24 1.83
The plot below shows measured power supply current into a TAS5766M. The dashed line
corresponds to 6.4A delivered into two 3.76-ohm loads using a 12V supply.
Figure 11.
Power Supply Current Measurement