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SHUTDOWN MODE
USING LOW-ESR CAPACITORS
THERMAL CONSIDERATIONS
160
40
20
0
0.25
1.50
0.5
0.75
1
RL = 16
–
Free-Air
T
emperature
–
Maximum Output Power – W
1.25
RL = 8
RL = 4
C
°
T A
80
60
120
100
140
VDD = 5 V
5-V VERSUS 3.3-V OPERATION
TPA4860
SLOS164B – SEPTEMBER 1996 – REVISED JUNE 2004
The TPA4860 employs a shutdown mode of operation designed to reduce quiescent supply current, IDD(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, IDD ~
0.6 A. 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 40 provides an easy way to determine what output power can be expected out of the TPA4860
for a given system ambient temperature in designs using 5-V supplies. This curve assumes no forced airflow or
additional heat sinking.
Figure 40. Free-Air Temperature Versus Maximum Continuous Output Power
The TPA4860 was designed for operation over a supply range of 2.7 V to 5.5 V. This data sheet provides full
specifications for 5-V and 3.3-V operation, as these are considered to be the two most common standard
voltages. There are no special considerations for 3.3-V versus 5-V operation as far as supply bypassing, gain
setting, or stability. Supply current is slightly reduced from 3.5 mA (typical) to 2.5 mA (typical). The most
important consideration is that of output power. Each amplifier in TPA4860 can produce a maximum voltage
swing of VDD – 1 V. This means, for 3.3-V operation, clipping starts to occur when VO(PP) = 2.3 V as opposed to
when VO(PP) = 4 V while operating at 5 V. The reduced voltage swing subsequently reduces maximum output
power into an 8-
load to less than 0.33 W before distortion begins to become significant.
Operation at 3.3-V supplies, as can be shown from the efficiency formula in Equation 4, consumes approximately
two-thirds the supply power for a given output-power level than operation from 5-V supplies. When the
application demands less than 500 mW, 3.3-V operation should be strongly considered, especially in
battery-powered applications.
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