NXP Semiconductors TFA9812 14.2 Output current limiting

TFA9812_2 © NXP B.V. 2009. All rights reserved.
Preliminary data sheet Rev. 02 — 22 January 2009 50 of 66
NXP Semiconductors TFA9812
BTL stereo Class-D audio amplifier with I2S input
δmax = Maximum duty factor (0.96).
The output power at 10 % THD can be estimated using Equation 11:
(11)
Figure 11 and Figure 12 show the estimated output power at THD = 0.5 % and
THD = 10 % as a function of BTL supply voltage for different load impedances.
14.2 Output current limiting
The peak output current is internally limited above a level of 3 A minimum. During normal
operation the output current should not exceed this threshold level of 3 A otherwise the
output signal will be distorted. The peak output current in BTL can be estimated using
Equation 12:
(12)
Where:
VP= supply voltage (V) (VDDP-VSSP)
RL= load impedance (Ω)
RDSon= 'On' resistance power switch (Ω)
RS= series resistance output inductor (Ω)
PO(10%) 1.25 PO(0.5%)⋅=
(1) 6 Ω
(2) 8 Ω
(3) 16 Ω
(1) 6 Ω
(2) 8 Ω
(3) 16 Ω
Fig 11. BTL PO (0.5 %) as a function of VPFig 12. BTL PO (10 %) as a function of VP
VP (V)
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10
20
30
0
(1)
(2)
(3)
PO (0.5 %)
(W/channel)
VP (V)
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15
30
45
0
(1)
(2)
(3)
PO (10 %)
W/channel
IO max()
VP
RL2+RDSon RS +〈〉⋅
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