apa3012 Anpec Electronics Corporation, apa3012 Datasheet - Page 15

• Manufacturer Part Number: apa3012
• Description: 3w Mono Low-voltage Audio Power Amplifier
• Manufacturer: Anpec Electronics Corporation

Effective Bypass Capacitor, C
As other power amplifiers, proper supply bypassing is
critical for low noise performance and high power supply
rejection.
The capacitors located on both the bypass and power
supply pins should be as close to the device as possible.
The effect of a larger bypass capacitor will improve PSRR
due to increased supply stability. Typical applications em-
ploy a 5V regulator with 1.0 F and a 0.1 F bypass capaci-
tor as supply filtering. This does not eliminate the need
for bypassing the supply nodes of the APA3012. The se-
lection of bypass capacitors, especially C
pendent upon desired PSRR requirements, click and pop
performance.
To avoid the start-up pop noise occurred, the bypass volt-
age should rise slower than the input bias voltage and
the relationship shown in equation (4) should be
maintained.
The bypass capacitor is fed thru from a 125k
inside the amplifier and the 40k
sistance of (R
4.7 F ceramic or tantalum low-ESR capacitors are rec-
ommended for the best THD and noise performance.
The bypass capacitance also effects to the start-up time.
It is determined in the following equation :
Power Supply Decoupling, Cs
The APA3012 is a high-performance CMOS audio ampli-
fier that requires adequate power supply decoupling to
ensure the output total harmonic distortion (THD) is as
low as possible. Power supply decoupling also prevents
the oscillations causing by long lead length between the
amplifier and the speaker. The optimum decoupling is
achieved by using two different type capacitors that target
on different type of noise on the power supply leads.
For higher frequency transients, spikes, or digital hash
on the line, a good low equivalent-series-resistance(ESR)
ceramic capacitor, typically 0.1 F placed as close as pos-
sible to the device V
frequency noise signals, a large aluminum electrolytic
capacitor of 10 F or greater placed near the audio power
Copyright
Rev. A.2 - Dec., 2008
Application Information (Cont.)
APA3012
Tstart up = 5 x (C
C
B
x 125k
1
i
ANPEC Electronics Corp.
+ R
f
). Bypass capacitor, C
DD
lead works best. For filtering lower-
B
<<
x 125k )
20k
B
1
is maximum input re-
x C
B
, values of 1 F to
i
B
, is thus de-
resistor
(4)
(5)
15
amplifier is recommended.
Optimizing Depop Circuitry
Circuitry has been included in the APA3012 to minimize
the amount of popping noise at power-up and when com-
ing out of shutdown mode. Popping occurs whenever a
voltage step is applied to the speaker. In order to elimi-
nate clicks and pops, all capacitors must be fully dis-
charged before turn-on. Rapid on/off switching of the de-
vice or the shutdown function will cause the click and pop
circuitry.
The value of C
Effective Bypass Capacitance) The bypass voltage ramp
up should be slower than input bias voltage. Although the
bypass pin current source cannot be modified, the size of
C
amount of clicks and pops. By increasing the value of C
turn-on pop can be reduced. However, the tradeoff for
using a larger bypass capacitor is to increase the turn-on
time for this device. There is a linear relationship be-
tween the size of C
A high gain amplifier intensifies the problem as the small
delta in voltage is multiplied by the gain. So, it is advanta-
geous to use low-gain configurations.
Shutdown Function
In order to reduce power consumption while not in use,
the APA3012 contains a shutdown pin to externally turn
off the amplifier bias circuitry. This shutdown feature turns
the amplifier off when a logic high is placed on the SHUT-
DOWN pin. The trigger point between a logic high and
logic low level is typically 1.6V. It is best to switch be-
tween the ground and the supply V
device performance.
By switching the SHUTDOWN pin to high, the amplifier
enters a low-current state, I
down mode. On normal operating, SHUTDOWN pin pulls
to a low level to keep the IC out of the shutdown mode.
The SHUTDOWN pin should be tied to a definite voltage
to avoid unwanted state changing.
BTL Amplifier Efficiency
An easy-to-use equation to calculate efficiency starts out
as being equal to the ratio of power from the power sup-
ply to the power delivered to the load.
B
can be changed to alter the device turn-on time and the
i
will also affect turn-on pops. (Refer to
B
and the turn-on time.
DD
< 1 A. APA3012 is in shut-
DD
to provide maximum
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B
,