Diodes PAM8902A - Manual (Page 8)

PAM8902A
Document number: DSxxxxx Rev. 1 - 3
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February 2013
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PAM8902A
A Product Line of
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Application Information
(cont.)
Input Capacitors (C
I
)
In the typical application, an input capacitor, C
I
, is required to allow the amplifier to bias the input signal to the proper DC level for optimum
operation. In this case, C
I
and the minimum input impedance R
I
form is a high-pass filter with the corner frequency determined in the follow
equation:
C R 2
1
f
I I
C
Π
=
It is important to consider the value of C
I
as it directly affects the low frequency performance of the circuit. For example, when R
I
is 150k and the
specification calls for a flat bass response are down to 150Hz.
Equation is reconfigured as followed:
R 2
1
C
IFC
I
Π
=
When input resistance variation is considered, the C
I
is 7nF, so one would likely choose a value of 10nF. A further consideration for this
capacitor is the leakage path from the input source through the input network (C
I
, R
I
+ R
F
) to the load. This leakage current creates a DC offset
voltage at the input to the amplifier that reduces useful headroom, especially in high gain applications. For this reason, a low-leakage tantalum or
ceramic capacitor is the best choice. When polarized capacitors are used, the positive side of the capacitor should face the amplifier input in
most applications as the DC level is held at V
DD
/2, which is likely higher than the source DC level. Please note that it is important to confirm the
capacitor polarity in the application.
Decoupling Capacitor
The PAM8902 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.
The optimum decoupling is achieved by using two different types of capacitors that target on 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-resistance (ESR) ceramic capacitor, typically
1µF is placed as close as possible to the device AVDD pin for the best operation. For filtering lower frequency noise signals, a large ceramic
capacitor of 10µF or greater placed near the AVDD supply trace is recommended.
External Schottky Diode
Use external schottky diode can get the best driving capability and efficiency.
Since internal power diode has limited driving capability, only in following conditions customer can remove the external schottky diode to reduce
the cost.
1. V
SET
= Low or Floating and C
L
less than 1µF.
2. The signal frequency less than 4KHz.
3. Haptic application (50–500Hz).
Shutdown Operation
In order to reduce power consumption while not in use, the PAM8902A contains shutdown circuitry amplifier off when a logic low is placed on the
ENA pin. By switching the ENA pin connected to GND, the PAM8902A supply current draw will be minimized in idle mode.
Under-Voltage Lock-Out (UVLO)
The PAM8902A incorporates circuitry designed to detect supply voltage. When the supply voltage drops to 2.2V or below, the PAM8902A goes
into a state of shutdown, and the device comes out of its shutdown state and restore to normal function only when reset the power supply or
ENA pin.
Over-Temperature Protection (OTP)
Thermal protection on the PAM8902A prevents the device from damage when the internal die temperature exceeds +150°C. There is a 15°C
tolerance on this trip point from device to device. Once the die temperature exceeds the set point, the device will enter the shutdown state and
the outputs are disabled, in this condition both OUTP and OUTN will become high impedance. This is not a latched fault. The thermal fault is
cleared once the temperature of the die decreased by 30°C. This large hysteresis will prevent motor boating sound well and the device begins
normal operation at this point with no external system interaction.