Diodes PAM8007 - Manual (Page 11)

PAM8007
Document number: DSxxxxx Rev. 1 - 2
11 of 17
www.diodes.com
October 2012
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PAM8007
A Product Line of
Diodes Incorporated
Application Information
Mute Operation
The MUTE pin is an input for controlling the output state of the PAM8007. A logic low on this pin disables the outputs, and a logic high on this
pin enables the outputs. This pin may be used as a quick disable or enable of the outputs without a volume fade. Quiescent current is listed in
the electrical characteristics table. The MUTE pin can be left floating due to the internal pull-up.
For the best power on/off pop performance, the amplifier should be placed in the MUTE mode prior to turning on/off the power
supply.
Shutdown Operation
In order to reduce power consumption while not in use, the PAM8007 contains shutdown circuitry to turn off the amplifier’s bias circuitry. The
amplifier is turned off when logic low is placed on the SHDN pin. By switching the SHDN pin connected to GND, the PAM8007 supply current
draw will be minimized in idle mode. The SHDN pin can be left floating due to the internal pull-up.
Line/Ear Operation
In order to control the speaker/headphone switch, the PAM8007 contains detect circuitry. When line/ear logic low, speaker actice; when logic
high, earphone active.
Power Supply Decoupling
The PAM8007 is a high performance CMOS audio amplifier that requires an adequate power supply decoupling to ensure the output THD and
PSRR are as low as possile. Power supply decoupling affects low frequency on the power supply leads for higher frey response. Optimum
decoupling is achieved by using two capacitors of different types that target different types of noise frequency tranisients, spike, or digital hash
on the line, a good low equivalent-series-resistance (ESR) ceramic capacitor, typically 1.0µF, placed as close as possible to the device V
DD
terminal works best. For filtering lower-frequency noise signals, a large capacitor of 10µF (ceramic) or greater placed near the audio power
amplifier is recommended.
Input Capacitor (C
I
)
Large input capacitors are both expensive and space hungry for portable designs. Clearly, a certai sized capacitor is needed to couple in low
frequencies without severe attenuation. But in many cases the speakers used in portable systems, whether internal or external, have little ability
to reproduce signals below 100Hz to 150Hz. Thus, using a large input capacitor may not increase actual system performance. In this case,
inout capacitor (C
I
) and input resistance (R
I
) of the amplifier form a high-pass filter with the corner frequency determined equation below;
C R 2
1
f
I I
C
Π
=
In addition to system cost and size, click and pop performance is affected by the size of the input coupling capacitor, C
I
. A larger inout coupling
capacitor requires more charge to reach its quiescent DC voltage (nominally ½ V
DD
). This charge comes from the internal circuit via the
feedback and is apt to create pops upon device enable. Thus, by minmizing the capacitor size based on necessary low frequency response,
turn-on pops can be minimized.
Analog Reference Bypass Capacitor (C
BYP
)
Analog Reference Bypass Capacitior (C
BYP
) is the most critical capacitor and serves several important functions. During start-up or recovery
from shutdown mode, C
BYP
determines the rate at which the amplifier starts up. The second function is to reduce noise produced by the power
supply caused by coupling into the output device signal. The noise is from the internal analog reference to the amplifier, which appears as
degraded PSRR and THD+N.
A ceramic bypass capacitor (C
BYP
) of 0.47µF to 1.0µF is recommended for the best THD and noise performance. Increasing the bypass
capacitor reduces clicking and popping noise from power on/off and entering and leaving shutdown.
Short Circuit Protection (SCP)
The PAM8007 has short circuit protection circuitry on the outputs that prevents the device from damage when output-to-output and output-to
GND short. When a short circuit is detected on the outputs, the outputs are disabled immediately. If the short was removed, the device
activates again.