tfa9879hn NXP Semiconductors, tfa9879hn Datasheet - Page 44

• Manufacturer Part Number: tfa9879hn
• Description: Mono Btl Class-d Audio Amplifier For Portable Applications With Digital Input
• Manufacturer: NXP Semiconductors

NXP Semiconductors
15. Application information
TFA9879_1
Preliminary data sheet
15.1.1 Estimating the RMS output power (P
15.1 Power capability
The TFA9879 is a filter-free BTL class-D amplifier that uses a fixed frequency PWM
modulation scheme (see the simplified application schematic in
TFA9879 is idle (no audio input signal), the voltage across the speaker is 0 V, generating
no additional current. Even when the PWM output is modulated by the audio input signal,
the out-of-band AC ripple current in the voice coil is very small compared to the audio
current. This is due to the inductive behavior of the voice coil at the PWM switching
frequency. A typical voice coil inductance is in the range 30 H to 80 H.
The RMS output power, P
using
where:
Example (clip control off):
With V
P
P
The RMS output power at THD + N = 10 % can be estimated using
P
P
P
o(RMS)1%
o(RMS)1%
o RMS
o RMS
0 RMS
Clip control off:
Clip control on:
R
R
R
V
M



DDP
L
S
DSon
max
= load resistance ()
= total series resistance of application
Equation
DDP
1%
1%
10%
= power supply voltage (V)
= maximum modulation depth (clip control on); typically 0.9
= on-resistance of power switch (typically 230 m)
= 1.35 W in an 8
= 2.35 W in a 4
= 5 V, R
=
=
=


--------------------------------------------------------------------------------------- -


-----------------------------------------------------------------------------------------------------------
1.25




11, with clip-control off, or using
All information provided in this document is subject to legal disclaimers.
----------------------------------------------------- -
R
----------------------------------------------------- -
R
L
L
+
+
DSon

R
R
P
S
S
0 RMS

+
+
= 0.23
Rev. 01 — 8 April 2010
R
R


o(RMS)
2
2
L
L

2

1%


load

R
R
load or

R
2
DSon
DSon
, at THD + N = 1 % just before clipping can be estimated
L

(at T
Mono BTL class-D audio amplifier with digital input
R


L




j


= 25
V
M
DDP
max
o(RMS)

C), R



2
V
Equation
DDP
)
S
= 0.14


2
12, with clip-control on.

:
Figure
Equation
TFA9879
18). When the
© NXP B.V. 2010. All rights reserved.
13:
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(12)
(13)
(11)