PAM8124 Datasheet, PDF (10/15 Pages) Diodes Incorporated – HIGH POWER AUDIO

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PAM8124
Application Information (cont.)
MUTE Operation
The MUTE pin is an input for controlling the output state of the PAM8124. A logic high on this pin causes the outputs to run at a constant 50%
duty cycle. A logic low on this pin enables the outputs. This pin may be used as a quick disable or enable of the outputs.
Shutdown Operation
The PAM8124 employs a shutdown operation mode to reduce supply current to the absolute minimum level during periods of non-use to save
power. The SDN input terminal should be pulling high during normal operation when the amplifier is in use. Pulling SDN low causes the outputs to
mute and the amplifier to enter a low-current state. SDN should never be left unconnected to prevent the amplifier from unpredictable operation.
For the best power-off pop performance, the amplifier should be set in shutdown mode prior to removing the power supply voltage.
For the best start-up pop performance, the amplifier should be set in mute mode prior to restarting the amplifier.
Internal Bias Generator Capacitor Selection
The internal bias generator (VCM) provides the internal bias for the preamplifier stage. The external input capacitors and this internal reference
allow the inputs to be biased within the optimal common-mode range of the input preamplifiers.
The selection of the capacitor value on the VCM terminal is critical for achieving the best device performance. During startup or recovery from
shutdown state the VCM capacitor determines the rate at which the amplifier starts up. The startup time is not critical for the best de-pop
performance since any heard pop sound is the result of the class-D output switching-on other than that of the startup time. However, at least a
0.47µF capacitor is recommended for the VCM capacitor.
Another function of the VCM capacitor is to bypass high frequency noise on the internal bias generator.
Power Supply Decoupling, CS
The PAM8124 is a high-performance CMOS audio amplifier that requires adequate power supply decoupling to ensure the output total harmonic
distortion (THD) as low as possible. Power supply decoupling also prevents oscillations caused by long lead between the amplifier and the
speaker. The optimum decoupling is achieved by using two capacitors of different types that target different types 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 of
0.1µF is typically recommended, placed as close as possible to the device's PVCC lead. To filter lower-frequency noises a large aluminium
electrolytic capacitor of 470µF or greater is recommended, placed near the audio power amplifier. The 10µF capacitor also serves as a local
storage capacitor for supplying current during large signal transients on the amplifier outputs.
BSL and BSR Capacitors
The half H-bridge output stages use NMOS transistors therefore requiring bootstrap capacitors for the high side of each output to turn on correctly.
A ceramic capacitor 220nF or more rated for over 25V must be connected from each output to its corresponding bootstrap input. Specifically, one
220nF capacitor must be connected from LOUT to BSL and another 220nF capacitor from ROUT to BSR. It is recommended to use 1μF BST
capacitor to replace 220nF for lower than 100Hz applications.
VCLAMP Capacitors
To ensure that the maximum gate-to-source voltage for the NMOS output transistors is not exceeded, an internal regulator is used to clamp the
gate voltage. A 1µF capacitor must be connected from VCLAMP to ground and must be rated for at least 25V. The voltages at the VCLAMP
terminals vary with VCC and may not be used to power any other circuitry.
Using Low-ESR Capacitors
Low-ESR capacitors are recommended throughout this application section. A real (with respect to ideal) capacitor can be modeled simply as a
resistor in series with an ideal capacitor. The voltage drop across this resistor minimizes the beneficial effects of the capacitor in the circuit. The
lower the equivalent value of this resistance the more the real capacitor behaves as an ideal capacitor.
Short-Circuit Protection
The PAM8124 has short circuit protection circuitry on the outputs to prevent damage to the device when output-to-output shorts (BTL mode),
output-to-GND shorts, or output-to-VCC shorts occur. Once a short-circuit is detected on the outputs, the output drive is immediately disabled.
This is not a latched fault. If the short was removed, the normal operation is restored.
PAM8124
Document number: DS36627 Rev. 1 - 2
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October 2013
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