PAM8009 datasheet(9/12 Pages) DIODES

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PAM8009

Document number: DS37224 Rev. 1 - 2

9 of 12

www.diodes.com

January 2015

PAM8009

Application Information (Cont.)

Input Capacitor (Ci)

Large input capacitors are both expensive and space hungry for portable designs. Clearly, a certain sized capacitor is needed to couple in low

frequency 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

Capacitor (Ci) and Input Resistance (Ri) of the amplifier form a high-pass filter with the corner frequency determined equation below:

Fc = 1/ 2πRi x Ci

In addition to system cost and size, click and pop performance is affected by the size of the input coupling capacitor, Ci. A larger in/out coupling

capacitor requires more charge to reach its quiescent DC voltage (Normally 1/2 VDD). This charge comes from the internal circuit via the feedback

and is apt to create pops upon device enabling. Thus, by minimizing the capacitor size based on necessary low frequency response, turn on pop

can be minimized.

Bypass Capacitor (CBYP)

Bypass Capacitor (CBYP) is the most critical capacitor and serves several important functions. During start-up or recovery from shutdown mode,

CBYP 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 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 0.47uF to 1.0uF 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.

Ordering Information

PAM8009 Datasheet(PDF) 9 Page - Diodes Incorporated