TAS5414 datasheet(37/44 Pages) TI

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Parallel Operation (PBTL)

DEMODULATION FILTER DESIGN

THERMAL INFORMATION

TAS5414

TAS5424

SLOS514 – FEBRUARY 2007

APPLICATION INFORMATION (continued)

TAS5414 and TAS5424 can be used to drive four 4

Ω loads, two 2Ω loads, or even one 1Ω load by paralleling

BTL channels on the load side of the LC output filter. For parallel operation, identical I2C settings are required

for any two paralleled channels (especially gain and current-limit settings) in order to have reliable system

performance and evenly dissipated power on multiple channels. Having identical gain and current-limit settings

can also prevent energy feeding back from one channel to the other. For smooth power up, power down, and

mute operation, the same control commands (such as mute, play, Hi-Z, etc.) should be sent to the paralleled

channels at the same time. Load diagnostic is also supported for parallel connection. Paralleling on the

TAS5414 and TAS5424 side of the LC output filter is not supported, and can result in device failure.

The TAS5414 and TAS5424 amplifier outputs are driven by high-current LDMOS transistors in an H-bridge

configuration. These transistors are either off or fully on. The result is a square-wave output signal with a duty

cycle that is proportional to the amplitude of the audio signal. It is recommended that a second-order LC filter be

used to recover the audio signal. The main purpose of the demodulation filter is to attenuate the high-frequency

components of the output signals that are out of the audio band. Design of the demodulation filter significantly

affects the audio performance of the power amplifier. Therefore, to meet the device THD+N specification, the

selection of the inductors used in the output filter should be carefully considered. The rule is that the inductance

should remain stable within the range of peak current seen at maximum output power and deliver approximately

µH of inductance at 16 A. If this rule is observed, the TAS5414 and TAS5424 should not have distortion issues

due to the output inductors. Another parameter to be considered is the idle-current loss in the inductor. This can

be measured or specified as inductor dissipation (D). The target specification for dissipation is less than 0.05. If

the dissipation factor is above this value, idle current increases. In general, 10-

µH inductors suffice for most

applications. The frequency response of the amplifier is slightly altered by the change in output load resistance;

however, unless tight control of frequency response is necessary (better than 0.5 dB), it is not necessary to

deviate from 10

µH.

The thermally augmented package provided with the TAS5414 and TAS5424 is designed to interface directly to

heat sinks using a thermal interface compound (for example, Artic Silver, Ceramique thermal compound.) The

heat sink then absorbs heat from the ICs and couples it to the local air. If louvers or fans are supplied, this

process can reach equilibrium and heat can be continually removed from the ICs. Because of the efficiency of

the TAS5414 and TAS5424, heat sinks can be smaller than those required for linear amplifiers of equivalent

performance.

RθJA is a system thermal resistance from junction to ambient air. As such, it is a system parameter with the

following components:

• Rθ

JC (the thermal resistance from junction to case, or in this case the heat slug)

• Thermal grease thermal resistance

• Heat sink thermal resistance

The thermal grease thermal resistance can be calculated from the exposed heat slug area and the thermal

grease manufacturer's area thermal resistance (expressed in

°C-in2/W or °C-mm2/W). The area thermal

resistance of the example thermal grease with a 0.001-inch (0.0254-mm) thick layer is about 0.007

°C-in2/W

(4.52

°C-mm2/W). The approximate exposed heat slug size is as follows:

TAS5424, 44-pin PSOP3

…………………. 0.124 in2 (80 mm2)

TAS5414, 36-pin PSOP3

…………………. 0.124 in2 (80 mm2)

Dividing the example thermal grease area resistance by the area of the heat slug gives the actual resistance

through the thermal grease for both parts:

TAS5424, 44-pin PSOP3

………………… 0.40°C/W

TAS5414, 36-pin PSOP3

………………… 0.40°C/W

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