NXP Semiconductors TDA8932B 14.2 Output current limiting, 14.3 Speaker conguration and impedance, 14.4 Single-ended capacitor

TDA8932B_3 © NXP B.V. 21 June 2007. All rights reserved.
Product data sheet Rev. 03— 21 June 2007 24 of 48
NXP Semiconductors TDA8932B
Class-D audio amplifier
14.2 Output current limiting
The peak output current IO(max) is internally limited above a level of 4 A (minimum). During
normal operation the output current should not exceed this threshold level of 4 A
otherwise the output signal is distorted. The peak output current in SE or BTL
configurations can be estimated using Equation 5 and Equation 6.
SE configuration:
(5)
BTL configuration:
(6)
Where:
VP= supply voltage VDDP1 − VSSP1 (V) or VDDP2 − VSSP2 (V)
RL= load impedance (Ω)
RDSon = on-resistance power switch (Ω)
Rs= series resistance output inductor (Ω)
RESR = equivalent series resistance SE capacitor (Ω)
Example:
A4Ωspeaker in the BTL configuration can be used up to a supply voltage of 18 V without
running into current limiting. Current limiting (clipping) will avoid audio holes but it causes
a comparable distortion like voltage clipping.
14.3 Speaker configuration and impedance
For a flat frequency response (second-order Butterworth filter) it is necessary to change
the low-pass filter components Llc and Clc according to the speaker configuration and
impedance. Table 14 shows the practical required values.
14.4 Single-ended capacitor
The SE capacitor forms a high-pass filter with the speaker impedance. So the frequency
response will roll-off with 20 dB per decade below f-3dB (3 dB cut-off frequency).
IO max()
0.5 VP ×
RLRDSon RsRESR +++
---------------------------------------------------------- 4A≤≤
IO max()
VP
RL2+RDSon Rs +()×
------------------------------------------------------4A≤≤
Table 14. Filter component values
Configuration RL (Ω) Llc (µH) Clc (nF)
SE 4 22 680
6 33 470
8 47 330
BTL 4 10 1500
6 15 1000
8 22 680