Datasheet

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SHUTDOWN MODE
USING LOW-ESR CAPACITORS
THERMAL CONSIDERATIONS
160
40
20
0
0 0.25 1.50.5 0.75 1
– Free-Air Temperature –
P
O
– Maximum Output Power – W
1.25
C
°
T
A
80
60
120
100
140
R
L
= 16 Ω
R
L
= 8 Ω
V
DD
= 5 V
TPA4861
SLOS163C – SEPTEMBER 1996 – REVISED JUNE 2004
Table 2. Common Load Impedances vs Low-Frequency
Output Characteristics in SE Mode
R
L
C
C
LOWEST FREQUENCY
8Ω 68 µF 293 Hz
32Ω 68 µF 73 Hz
47,000 Ω 68 µF 0.05 Hz
As Table 2 indicates, most of the bass response is attenuated into 8-Ω loads, while headphone response is
adequate and drive into line level inputs (a home stereo for example) is good.
The TPA4861 employs a shutdown mode of operation designed to reduce supply current, I
DD(q)
, to the absolute
minimum level during periods of nonuse for battery-power conservation. For example, during device sleep modes
or when other audio-drive currents are used (i.e., headphone mode), the speaker drive is not required. The
SHUTDOWN input terminal should be held low during normal operation when the amplifier is in use. Pulling
SHUTDOWN high causes the outputs to mute and the amplifier to enter a low-current state, I
DD(SD)
~ 0.6 µA.
SHUTDOWN should never be left unconnected because amplifier operation would be unpredictable.
Low-ESR capacitors are recommended throughout this applications section. A real capacitor can be modeled
simply as a resistor in series with an ideal capacitor. The voltage drop across this resistor minimizes the
beneficial effects of the capacitor in the circuit. The lower the equivalent value of this resistance, the more the
real capacitor behaves like an ideal capacitor.
A prime consideration when designing an audio amplifier circuit is internal power dissipation in the device. The
curve in Figure 39 provides an easy way to determine what output power can be expected out of the TPA4861
for a given system ambient temperature in designs using 5-V supplies. This curve assumes no forced airflow or
additional heat sinking.
Figure 39. Free-Air Temperature vs Maximum Continuous Output Power
19