Diodes PAM8406 - Manual (Page 9)

PAM8406
Document number: DSxxxxx Rev. 1 - 0
9 of 14
www.diodes.com
March 2013
© Diodes Incorporated
PAM8406
A Product Line of
Diodes Incorporated
Application Information
Application Note
1. When the PAM8406 works in Class-D with LC filters, it should be connected with the speaker before it's powered on, otherwise it will be
damaged easily.
2. When the PAM8406 works without LC filters, it's better to add a ferrite chip bead at the outgoing line of speaker for suppressing the possible
electromagnetic interference.
3. The recommended operating voltage is 5.5V. When the PAM8406 is powered with four battery cells, it should be noted that the voltage of four
new dry or alkaline batteries is over 6.0V, higher than its operation voltage, which will probably damage the device. Therefore, it's
recommended to use either four Ni-MH (Nickel Metal Hydride) rechargeable batteries or 3 dry or alkaline batteries.
4. One should not make the input signal too large. Large signal can cause the clipping of output signal when increasing the volume. This will
damage the device because of big gain of the PAM8406.
Test Setup for Performance Testing
Notes:
1. The AP AUX-0025 low pass filter is necessary for Class-D amplifier measurement with AP analyzer.
2. Two 22μH inductors are used in series with load resistor to emulate the small speaker for efficiency measurement.
Maximum Gain
As shown in block diagram (Page 2), the PAM8406 has two internal amplifier stages. The first stage's gain is externally configurable, while the
second stage's is internally fixed. The closed-loop gain of the first stage is set by selecting the ratio of R
F
to R
I
while the second stage's gain is
fixed at 2x.The output of amplifier 1 serves as the input to amplifier 2, thus the two amplifiers produce signals identical in magnitude, but different
in phase by 180°. Consequently, the differential gain for the IC is
A
VD
= 20*log [2*(R
F
/R
I
)]
The PAM8406 sets maximum R
F
=142kΩ, minimum R
I
=18kΩ, so the maximum closed-gain is 24dB.
Mode Selection
When mode pin high, it features Class-D; mode pin low, it’s class AB. Mode pin can’t be floating.
Mute Operation
The MUTE pin is an input for controlling the output state of the PAM8406. A logic low on this pin disables the outputs, and a logic high on this pin
enables the outputs. This pin may be used as a quick disable or enable of the outputs without a volume fade. Quiescent current is listed in the
electrical characteristic table. The
MUTE pin can be left floating due to the internal pull-up.
Shutdown Operation
In order to reduce power consumption while not in use, the PAM8406 contains shutdown circuitry to turn off the amplifier's bias circuitry. This
shutdown feature turns the amplifier off when logic low is applied to the SHDN pin. By switching the SHDN pin connected to GND, the PAM8406
supply current draw will be minimized in idle mode. The SHDN pin can be left floating due
to the internal pull-up.