Diodes PAM8001 - Manual (Page 12)

PAM8001
Document number: DSxxxxx Rev. 1 - 0
12 of 17
www.diodes.com
February 2013
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PAM8001
A Product Line of
Diodes Incorporated
Application Information
(cont.)
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.
Power Supply Decoupling
The PAM8001 is a high performance CMOS audio amplifier that requires adequate power supply decoupling to ensure the output THD and
PSRR are as low as possible. 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 transients, spikes, 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-frequecny 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 certain 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,
input capacitior (C
I
) and input resistance (R
I
) of the amplifier form a high-pass filter with the corner frequency determined equation below,
I I
C R 2
1
fc


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 input 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 minimizing the capacitor size based on necessary low frequency response,
turn-on pops can be minimized.
Analog Reference Bypass Capacitor (C
BYP
)
The Analog Reference Bypass Capacitor (C
BYP
) at V
DD
/2 pin, 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 drive signal. The noise is from the internal analog reference to the amplifier,
which appears as degraded PSRR and THD+N.
A ceramic bypass capacitor (CBYP) 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 leaving shutdown.
Under Voltage Lock-Out (UVLO)
The PAM8001 incorporates circuitry designed to detect when supply voltage is low. When the supply voltage drops to 1.8V or below, the
PAM8801 outputs are disabled and the device comes out of this state and states to normal fucntional once V
DD
≥ 2.0V.
Short Circuit Protection (SCP)
The PAM8001 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.
Over Temperature Protection
Thermal protection on the PAM8001 prevents the device from damage when the internal die temperature exceeds 150°C. There is a 15 degree
tolerance on this trip point from device to device. Once the die temperature exceeds the thermal set point, the device outputs are disabled. This
is not a latched fault. The thermal fault is cleared once the temperature of the die is reduced by 30°C. This large hysteresis will prevent motor
boating sound well. The device begins normal operation at this point without external system interaction.