Diodes PAM8610 - Manual (Page 11)

PAM8610
Document number: DSxxxxx Rev. 1 - 2
11 of 15
www.diodes.com
June 2013
© Diodes Incorporated
PAM8610
A Product Line of
Diodes Incorporated
Application Information
(cont.)
Volume Control
A DC volume control section is integrated in PAM8610, controlling via V
REF
, VOLUME and V
REFGND
terminals. The voltage on VOLUME pin,
without exceeding V
REF
, determines internal amplifier gain as listed in Table 1.
If a resistor divider is used to fix gain of the amplifier, the V
REF
terminal can be directly connected to AV
DD
and the resistor divider connected
across V
REF
and REFGND. For fixed gain, the resistor divider values are to center the voltage given in the Table 1.
FADE Operation
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.
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.
MUTE Operation
The MUTE pin is an input for controlling the output state of the PAM8610. 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.
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.
Shutdown Operation
The PAM8610 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.
For the best power-off pop performance, the amplifier should be set in shutdown mode prior to removing the power supply voltage.
Internal 2.5V Bias Generator Capacitor Selection
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.
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
0.47 μF capacitor is recommended for the V2P5 capacitor.
Another function of the V2P5 capacitor is to filter high frequency noise on the internal 2.5V bias generator.
Power Supply Decoupling, C
S
The PAM8610 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 1 μF, is recommended, placing as close as possible to the device’s V
CC
lead. To filter lower-frequency noises, a large aluminum
electrolytic capacitor of 10 μF 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.