TDA8922 PHILIPS [NXP Semiconductors], TDA8922 Datasheet - Page 18

• Manufacturer Part Number: TDA8922
• Description: 2 x 25 W class-D power amplifier
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
To trigger the maximum current protection in the
TDA8922, the required output current must exceed 4 A.
This situation occurs in case of:
Even if load impedances are connected to the amplifier
outputs which have an impedance rating of 4 , this
impedance can be lower due to the frequency
characteristic of the loudspeaker; practical loudspeaker
impedances can be modelled as an RLC network which
will have a specific frequency characteristic: the
impedance at the output of the amplifier will vary with the
input frequency. A high supply voltage in combination with
a low impedance will result in large current requirements.
Another factor which must be taken into account is the
ripple current which will also flow through the output power
switches. This ripple current depends on the inductor
values which are used, supply voltage, oscillator
frequency, duty factor and minimum pulse width. The
maximum available output current to drive the load
impedance can be calculated by subtracting the ripple
current from the maximum repetitive peak current in the
output pin, which is 4 A for the TDA8922.
As a rule of thumb the following expressions can be used
to determine the minimum allowed load impedance
without generating audio holes:
Where:
See the application notes (tbf) for a more detailed
description of the implications of output current limiting.
2003 Mar 20
Z
Z
L
L
Short-circuits from any output terminal to the supply
lines (V
Short-circuit across the load or speaker impedances or
a load impedance below the specified values of
4 and 8 .
Z
f
t
V
(so, if the supply is 30 V symmetrical, then V
I
see also Chapter 9
I
2
osc
min
ORM
ripple
L
P
V
---------------------------------------------------- - 0.6
2V
-------------------------------------------------------- - 1.2
= load impedance
= single-sided supply voltage
= oscillator frequency
= minimum pulse width (typical 190 ns)
P
= maximum repetitive peak current in output pin;
= ripple current.
25 W class-D power amplifier
P
I
DD
ORM
I
ORM
1 t
1 t
or V
–
–
–
–
min
I
min
SS
ripple
I
ripple
)
f
osc
f
osc
–
–
for SE application.
for BTL application.
P
= 30 V)
18
16.7
The TDA8922 class-D amplifier is supplied by a
symmetrical voltage (e.g V
When the amplifier is used in a SE configuration, a
so-called ‘pumping effect’ can occur. During one switching
interval, energy is taken from one supply (e.g. V
a part of that energy is delivered back to the other supply
line (e.g. V
source cannot sink energy, the voltage across the output
capacitors of that voltage supply source will increase:
the supply voltage is pumped to higher levels. The voltage
increase caused by the pumping effect depends on:
The pumping effect should not cause a malfunction of
either the audio amplifier and/or the voltage supply source.
For instance, this malfunction can be caused by triggering
of the undervoltage or overvoltage protection or unbalance
protection of the amplifier.
See the application notes (tbf) for a more detailed
description of the implications of output current limiting.
16.8
The reference design for a single-chip class-D audio
amplifier using the TDA8922TH is illustrated in Fig.10.
The Printed-Circuit Board (PCB) layout is shown in Fig.11.
The Bill Of Materials (BOM) is given in Table 1.
16.9
The size of the PCB is 74.3
copper with 121 metallized through holes.
The standard configuration has a symmetrical supply
(typical 20 V) with stereo SE outputs (typical 2
The PCB is also suitable for a mono BTL configuration
(1
It is possible to use several different output filter inductors
such as 16RHBP or EP13 types to evaluate the
performance against the price or size.
16.10 Classification
The application shows optimized signal and EMI
performance.
Speaker impedance
Supply voltage
Audio signal frequency
Capacitor value present on supply lines
Source and sink currents of other channels.
8 ) with symmetrical and asymmetrical supply.
Pumping effects
Reference design
PCB information for HSOP24 package
SS
) and visa versa. When the voltage supply
DD
59.10 mm, dual sided 35 m
= +25 V and V
Objective specification
TDA8922
SS
= 25 V).
DD
8 ).
), while