Diodes PAM8615 - Manual (Page 10)

PAM8615
Document number: DSxxxxx Rev. 1 - 1
10 of 14
www.diodes.com
October 2012
© Diodes Incorporated
PAM8615
A Product Line of
Diodes Incorporated
Application Information
(cont.)
Shutdown Operation
The PAM8615 employs a shutdown operation mode to reduce supply current to the absolute minimum level during periods of non-use to save
power. The SD input terminal should be pull high during normal operation when the amplifier is in use. Pulling SD low causes the outputs to mute
and the amplifier to enter a low-current state. SD 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.
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 PAM8615 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-seriesresistance (ESR) ceramic capacitor,
typically 0.1μF, is recommended, placing as close as possible to the device's PVCC lead. To filter lower-frequency noises, a large aluminum
electrolytic capacitor of 470μF or greater is recommended, placing 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.
Selection of ROSC
The switching frequency is determined by the values of components connected to ROSC (pin 19) and calculated with the following equation:
F 21 x R
68 . 0
f
p OSC
OSC
=
The recommended values is R
OSC
= 100KΩ for a switching frequency of 323kHz.
BST_A and BST_B Capacitors
The half H-bridge output stages use NMOS transistors only. They therefore require bootstrap capacitors for the high side of each output to turn
on correctly. An at least 220nF ceramic capacitor, rated for at least 25V, must be connected from each output to its corresponding bootstrap
input. Specifically, one 220nF capacitor must be connected from OUT_A to BST_A, and another 220nF capacitor from OUT_B to BST_B. 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 not exceeded, two internal regulators are used to clamp the
gate voltage. A 1μF capacitors 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.
Internal Regulated 5-V Supply (AVDD)
The AVDD terminal is the output of an internallygenerated 5V supply, used for the oscillator, preamplifier, and volume control circuitry. It requires
a 0.1μF to 1μF capacitor, placed very close to the pin to Ground to keep the regulator stable. The regulator may not be used to power any
external circuitry.