apa0712 Anpec Electronics Corporation, apa0712 Datasheet - Page 15

• Manufacturer Part Number: apa0712
• Description: 1.4w Mono Audio Low-voltage Audio Power Amplifier
• Manufacturer: Anpec Electronics Corporation

Application Descriptions (Cont.)
Optimizing Depop Circuitry (Cont.)
range of 0.22 F to 0.47 F, C
should produce a virtually click-less and pop-less
turn-on.
A high gain amplifier intensifies the problem as the
small delta in voltage is multiplied by the gain. So it is
advantageous to use low-gain configurations.
Shutdown Function
In order to reduce power consumption while not in use,
the APA0712 contains a shutdown function to externally
turn off the amplifier bias circuitry. This shutdown
feature turns the amplifier off when logic low is placed
on the SD pin for APA0712. The trigger point between
a logic high and logic low level is typically 0.4V
best to switch between ground and the supply voltage
V
switching the SD pin to low level, the amplifier enters
a low-consumption-current state, I
shutdown mode. On normal operating, APA0712’ s
SD pin should pull to high level to keeping the IC out
of the shutdown mode. The SD pin should be tied to a
definite voltage to avoid unwanted state changes.
BTL Amplifier Efficiency
An easy-to-use equation to calculate efficiency starts
out as being equal to the ratio of power from the power
supply to the power delivered to the load. The following
equations are the basis for calculating amplifier
efficiency.
Where:
Copyright
Rev. A.2 - Aug., 2007
APA0712
DD
Efficiency
P
P
to provide maximum device performance. By
V
O
SUP
O.RMS
V
O.RMS
V
R
ANPEC Electronics Corp.
DD
V
L
2
P
2
P
I
P
SUP
DD.AVG
O
2R
V
P
2
L
V
DD
B
2V
being equal to 2.2 F
R
DD
P
L
for APA0712 is in
DD
(6)
(7)
(8)
(9)
. It is
15
Efficiency of a BTL configuration:
Table 1 employs equation10 to calculate efficiencies
for four different output power levels when load is 8 .
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 near 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 mono 1.4W audio system with 8 loads
and a 5V supply, the maximum draw on the power
supply is almost 1.5W.
**High peak voltages cause the THD+N to increase.
Table 1. Efficiency Vs Output Power in 5-V/8
Amplifier Systems
A final point to remember about linear amplifiers (either
SE or BTL) is how to manipulate the terms in the
efficiency equation to utmost advantage when
possible. Note that in equation10, V
denominator.
This indicates that as V
up. In other words, use the efficiency analysis to
choose the correct supply voltage and speaker
impedance for the application.
Power Dissipation
Whether the power amplifier is operated in BTL or SE
modes, power dissipation is a major concern. In equa-
Po (W)
0.2
0.5
0.7
1.0
P
P
SUP
O
V
Efficiency (%)
DD
2R
V
28.34
44.94
53.12
63.59
P
2
L
2V
R
P
L
DD
4V
goes down, efficiency goes
V
DD
I
P
DD
0.14
0.22
0.26
0.32
(A)
www.anpec.com.tw
V
1.79
2.83
3.35
4.00
PP
(V)
DD
Differential
is in the
(10)
P
0.55
0.55
0.50
0.35
D
(W)