PAM8606
6W Stereo Class-D Audio Power Amplifier with DC Volume Control
Volume Control
Shutdown Operation
A DC volume control section is integrated in
PAM8606, controlling via VREF, VOLUME and
VREFGND terminals. The voltage on VOLUME
pin, without exceeding VREF, determines internal
amplifier gain as listed in Table 1.
The PAM8606 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 held 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.
If a resistor divider is used to fix gain of the
amplifier, the VREF terminal can be directly
connected to AVDD and the resistor divider
connected across VREF and REFGND. For fixed
gain, the resistor divider values are calculated to
center the voltage given in the Table 1.
For the best power-off pop performance, the
amplifier should be set in shutdown mode prior to
removing the power supply voltage.
FADE Operation
Internal 2.5V Bias Generator Capacitor
Selection
The FADE terminal is a logic input that controls
the operation of the volume control circuitry
during transitions to and from the shutdown state
and during power-up.
The internal 2.5V bias generator (V2P5) 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.
A logic low on this terminal will set the amplifier in
fade mode. During power-up or recovery from the
shutdown state (a logic high is applied to the SD
terminal), the volume is smoothly ramped up from
the mute state, -75dB, to the desired volume set
by the voltage on the volume control terminal.
Conversely, the volume is smoothly ramped down
from the current state to the mute state when a
logic low is applied to the SD terminal. A logic high
on this pin disables the volume fade effect during
transitions to and from the shutdown state and
during power-up. During power-up or recovery
from the shutdown state (a logic high is applied to
the SD terminal), the transition from the mute
state, -75dB, to the desired volume setting is less
than 1ms. Conversely, the volume ramps down
from current state to the mute state within 1ms
when a logic low is applied to the SD terminal.
The selection of the capacitor value on the V2P5
terminal is critical for achieving the best device
performance. During startup or recovery from
shutdown state, the V2P5 capacitor determines
the rate at which the amplifier starts up. When the
voltage on the V2P5 capacitor equals 0.75 x
V2P5, or 75% of its final value, the device turns
on and the class-D outputs start switching. 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 V2P5
capacitor.
MUTE Operation
Another function of the V2P5 capacitor is to filter
high frequency noise on the internal 2.5V bias
generator.
The MUTE pin is an input for controlling the output
state of the PAM8606. A logic high on this pin
disables the outputs and low enables the outputs.
This pin may be used as a quick disable or enable
of the outputs without a volume fade.
Power Supply Decoupling, CS
The PAM8606 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
For power saving, the SD pin should be used to
reduce the quiescent current to the absolute
minimum level. The volume will fade, increasing
or decreasing slowly, when leaving or entering the
shutdown state if the FADE terminal is held low. If
the FADE terminal is held high, the outputs will
transit very quickly. Refer to the FADE operation
section.
Power Analog Microelectronics,Inc
www.poweranalog.com
08/2008 Rev 1.1
13
PAM [ POWER ANALOG MICOELECTRONICS ]
