2 output current limiting, Tfa9812, Nxp semiconductors – NXP Semiconductors TFA9812 User Manual
Page 50
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 I
2
S input
δ
max
= Maximum duty factor (0.96).
The output power at 10 % THD can be estimated using
:
(11)
and
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
(12)
Where:
V
P
= supply voltage (V) (V
DDP
-V
SSP
)
R
L
= load impedance (
Ω
)
R
DSon
= 'On' resistance power switch (
Ω
)
R
S
= series resistance output inductor (
Ω
)
P
O
(10%)
1.25 P
O
(0.5%)
⋅
=
(1) 6
Ω
(2) 8
Ω
(3) 16
Ω
(1) 6
Ω
(2) 8
Ω
(3) 16
Ω
Fig 11. BTL P
O
(0.5 %) as a function of V
P
Fig 12. BTL P
O
(10 %) as a function of V
P
V
P
(V)
8
24
20
12
16
010aaa347
10
20
30
0
(1)
(2)
(3)
P
O
(0.5 %)
(W/channel)
V
P
(V)
8
24
20
12
16
010aaa348
15
30
45
0
(1)
(2)
(3)
P
O
(10 %)
W/channel
I
O max
(
)
V
P
R
L
2
+
R
DSon
R
S
+
〈
〉
⋅
-----------------------------------------------------
≤