TDF8599BTH datasheet(35/54 Pages) NXP

35 / 54 page

NXP Semiconductors

TDF8599B

I2C-bus controlled dual channel 43 W/2 Ohm, single channel 85 W/1 Ohm class-D power amplifier with

load diagnostics

TDF8599B

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 2 — 23 August 2016

35 / 54

Table 22. Filter component values

Load impedance (Ω)

LLC (μH)

CLC (μF)

2.5

4.4

2.2

Remark: When using a 1 Ω load impedance in Parallel mode, the outputs are shorted

after the low-pass filter switches two 2 Ω filters in parallel.

14.5 Heat sink requirements

In most applications, it is necessary to connect an external heat sink to the TDF8599B.

Thermal foldback activates at Tj = 140 °C. The expression below shows the relationship

between the maximum power dissipation before activation of thermal foldback and the

total thermal resistance from junction to ambient:

(7)

Pmax is determined by the efficiency (η) of the TDF8599B. The efficiency measured as a

function of output power is given in Figure 43. The power dissipation can be derived as a

function of output power (see Figure 42).

Example 1:

• VP = 14.4 V

• Po = 2 × 25 W into 4 Ω (THD = 10 % continuous)

• Tj(max) = 140 °C

• Tamb = 25 °C

• Pmax = 5.8 W (from Figure 42)

• The required Rth(j-a) = 115 °C / 5.8 W = 19 K/W

The total thermal resistance Rth(j-a) consists of: Rth(j-c) + Rth(c-h) + Rth(h-a)

Where:

• Thermal resistance from junction to case (Rth(j-c)) = 1 K/W

• Thermal resistance from case to heat sink (Rth(c-h)) = 0.5 K/W to 1 K/W (depending on

mounting)

• Thermal resistance from heat sink to ambient (Rth(h-a)) would then be 19 - (1 + 1) = 17

K/W.

If an audio signal has a crest factor of 10 (the ratio between peak power and average

power = 10 dB) then Tj will be much lower.

Example 2:

• VP = 14.4 V

• Po = 2 × (25 W / 10) = 2 × 2.5 W into 4 Ω (audio with crest factor of 10)

• Tamb = 25 °C

• Pmax = 2.5 W

• Rth(j-a) = 19 K/W

• Tj(max) = 25 °C + (2.5 W × 19 K/W) = 72 °C

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