TPA6010A4_07 Datasheet, PDF (16/25 Pages) Texas Instruments – STEREO 2.7-W AUDIO POWER AMPLIFIER WITH BASS BOOST AND DC VOLUME CONTROL

TPA6010A4
SLOS268B – JUNE 2000 – REVISED AUGUST 2004
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I_DD
V_(LRMS)
I_DD(avg)
Figure 12. Voltage and Current Waveforms for BTL Amplifiers
Although the voltages and currents for SE and BTL are sinusoidal in the load, currents from the supply are very
different between SE and BTL configurations. In an SE application the current waveform is a half-wave rectified
shape whereas in BTL it is a full-wave rectified waveform. This means RMS conversion factors are different.
Keep in mind that for most of the waveform both the push and pull transistors are not on at the same time, which
supports the fact that each amplifier in the BTL device only draws current from the supply for half the waveform.
Equation 8 and Equation 9 are the basis for calculating amplifier efficiency.
Efficiency of a BTL amplifier +
P_L
P_SUP
(8)
Where:
P_L
+
V_Lrms²
R_L
,
and V_LRMS
+
V_P
Ǹ₂
,
therefore,
P_L
+
V
2
P
2 R_L
and
P_SUP + V_DD I_DDavg
and
ŕ I_DDavg
+
1
p
p
0
V_P
R_L
sin(t) dt
+
*
1
p
V_P
R_L
[cos(t)]
p
0
+
2V_P
p R_L
Therefore,
P_SUP
+
2 V_DD V_P
p R_L
Substituting P_L and P_SUP into equation 8,
V_P²
Efficiency of a BTL amplifier
+ ^{2 RL}
2 V_DD V_P
+
p V_P
4 V_DD
Where:
p R_L
V_P + Ǹ2 P_L R_L
Therefore,
h_BTL
+
p
Ǹ2 P_L R_L
4 V_DD
P_L = Power delivered to load
P_SUP = Power drawn from power supply
V_LRMS = RMS voltage on BTL load
R_L = Load resistance
V_P = Peak voltage on BTL load
I_DDavg = Average current drawn from
the power supply
V_DD = Power supply voltage
η_BTL = Efficiency of a BTL amplifier
(9)
Table 4 employs equation 9 to calculate efficiencies for four different output power levels. Note that the efficiency
of the amplifier is quite low for lower power levels and rises sharply as power to the load is increased, resulting in
a nearly flat internal power dissipation over the normal operating range. Note that the internal dissipation at full
output power is less than in the half power range. Calculating the efficiency for a specific system is the key to
proper power supply design. For a stereo 1-W audio system with 8-Ω loads and a 5-V supply, the maximum draw
on the power supply is almost 3.25 W.
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