Evaluation Board Operation; Input-Blocking Capacitors; Charge Pump Flying Capacitor And Pvss Capacitor; Decoupling Capacitors - ISSI IS31AP4915 Quick Start Manual

IS31AP4915 Class-G Audio Power Amplifier Evaluation Board Guide

Evaluation Board Operation

The evaluation board provided features the IS31AP4915 Class-G audio power amplifier IC, a ceramic
amplifier ideal in applications that require high efficiency. The board requires a DC power supply range of
3.5V to 6.5V, with constant 2A supply current. The board accepts stereo input. The audio source is amplified
to provide an 11V output voltage to drive ceramic speaker. It is shipped with a fixed gain of 48 V/V.
P-P

Input-Blocking Capacitors

A series of DC, input-blocking, capacitors are required to be placed following the audio signal input circuitry.
This capacitor block the DC portion of the audio source and allow the IS31AP4915 inputs to be properly
biased to provide maximum performance. These capacitors form a high-pass filter with the input impedance
of the IS31AP4915. The cutoff frequency is calculated using Equation (1). For this calculation, the
capacitance used is the input-blocking capacitor and the resistance is the input impedance of the
IS31AP4915. Because the gains of both the IS31AP4915 is fixed, the input impedance remains a constant
value. Using the input impedance value from the operating characteristics table, the frequency and/or
capacitance can be determined when one of the two values is given.

Charge Pump Flying Capacitor and PVSS Capacitor

The charge pump flying capacitor serves to transfer charge during the generation of the negative supply
voltage. The PVSS capacitor must be at least equal to the charge pump capacitor in order to allow
maximum charge transfer. Low ESR capacitors are an ideal selection, and a value of 10μF is typical.
Capacitor values that are smaller than 10μF can be used, but the maximum output power is reduced and
the device may not operate to specifications

Decoupling Capacitors

The IS31AP4915 require adequate power supply decoupling to ensure that the noise and total harmonic
distortion (THD) are low. A good low equivalent-series-resistance (ESR) ceramic capacitor, typically 1μF,
placed as close as possible to the device VDD lead works best. Placing this decoupling capacitor close to
the IS31AP4915 is important for the performance of the amplifier. For filtering lower frequency noise signals,
a 10μF or greater capacitor placed near the audio power amplifier would also help, but it is not required in
most applications because of the high PSRR of this device.

Layout Recommendations

Exposed Pad Option for IS31AP4915 Package
The exposed metal bonding pad on the device package must be soldered down to pads on the PCB for
enhanced reliability. The pad on the PCB must be soldered to a floating plane.
Caution: Do NOT connect to power or ground.

SGND and PGND Connections

The SGND and PGND pins of the IS31AP4915 must be routed separately back to the decoupling capacitor
in order to provide proper device operation. If the SGND and PGND pins are connected directly to each
other, the part functions without risk of failure, but the noise and THD performance do not meet the
specifications.

Software Support

Please refer to the integrated software program that comes with the evaluation board.
Integrated Silicon Solution, Inc. –
2
http://www.issi.com
RevA, 1/10/2013