ANALOG PRODUCTS DIVISION

561 E. Elliot Road #175 Chandler, AZ 85225 Tel: (480) 539-2900. Fax: (602) 431-2288

www.protekanalog.com

72

PA4101

PUNK with µP Supervisor

95000 Rev. 0. 01/08

NOT FOR USE IN LIFE SUPPORT SYSTEMS

Timing Diagram Supervisor

THEORY OF OPERATION Audio Muting

STARTUP

During Startup, the Power supply ramps from 0V to VCC.

This time is usually in excess of 20ms. As soon

as this change in voltage is sensed, PUNK latches the

Mute Controller outputs to HIGH, thus “muting” the lines.

This is the Startup Operation (figure 1). The duration for

which the controller outputs are latched

HIGH can be controlled by an external RC circuit.

When the voltage at this RC pin reaches a certain

threshold, the mute controller releases the lines

(Gate voltage is LOW) and Normal Operation starts.

SHUTDOWN

During Shutdown, the reverse process happens. As the

power supply reaches the threshold on its way down, the

mute controller again latches the outputs to HIGH, thus

“muting” the lines (figure 2). This muting prevents

unwanted signal spikes from getting to the power

amplifiers. However, for optimal performance, it is

suggested to mute the lines using the MUTECONT signal

before power down. This process will ensure that the pop

noise involved during shutdown is diminished

SOFTMUTE

During normal operation, PUNK is in OFF state. But if

there arises a situation when the audio lines need

to be muted, the designer can do this by asserting the

MUTECONT signal to HIGH. This will initiate a

SOFTMUTE sequence (figure 3). When the

MUTECONT signal is asserted, the mute controller

gradually ramps the control voltages in a “SOFT”

fashion so as to provide a soft mute operation. The

mute delay is fully controllable by the designer by using

an external capacitor at CEXT. Typical values of CEXT

are between 0.1μF and 0.5μF. The reverse happens

when the MUTECONT signal is released. This

operation is explained in detail in the Application Circuit

section.

Figure 1: Startup Pop-Noise Reduction

Figure 2: Shutdown Pop-Noise Reduction

Figure 3: SOFT mute operation

RESET