High-Power Stereo Class-D Audio Power Amplifier
SGM4703 with Adjustable Power Limit and Automatic Level Control
6
DECEMBER 2022
SG Micro Corp
www.sg-micro.com
IMPORTANT APPLICATION NOTES
Output Power Considerations
1. The maximum output power of SGM4703 is
determined primarily by the power supply (its output
voltage and current) and speaker impedance. As a high
power audio amplifier, the maximum output power of
SGM4703 can be severely limited by the thermal
dissipation capability of the system board layout.
2. The SGM4703 is packaged with an exposed thermal
pad on the underside of the device. Solder the thermal
pad directly onto a large grounded metal island (GND)
underneath the package, as a thermal sink for proper
thermal dissipation. On the grounded metal island,
place several rows of solid, equally-spaced vias
connecting to the bottom layer of the system board.
Failure to do so can severely limit its thermal
dissipation capability. It might even cause the device
going into over-temperature mute occasionally.
3. Use wide open areas around the SGM4703 on the
top and bottom layers of the system board as the
ground plane GND. Place lots of solid vias connecting
the top and bottom layers of GND. Furthermore, for
proper thermal dissipation, reserve wide and
uninterrupted GND areas along the thermal flow on the
top layer, i.e., no wires cutting through the GND layer
and obstructing the thermal flow in the proximity of the
device.
4. All the power ground pins PGND are directly shorted
to the ground plane GND as a central “star” ground for
the SGM4703. Use a single point of connection
between the analog ground AGND and the ground
plane GND to minimize the coupling of high-current
switching noise onto audio signals.
5. The power supply pins, PVDD, for the audio
amplifiers’ output stages are directly connected
together with short and wide metal traces.
6. Use direct and low-impedance traces from the audio
outputs (VOPL/R and VONL/R) to their individual
output filters and speakers.
Output Filter Considerations
7. For most applications, the SGM4703 does not
require an LC output filter when speaker wires are less
than 10cm.
8. A ferrite bead filter constructed from a ferrite bead
and a ceramic capacitor can be used to suppress EMI.
Choose a ferrite bead with a rated current no less than
4A for 8Ω loads, 7A for 4Ω loads, and 9A for 3Ω or less
loads (in PBTL configuration). Place the filter tightly
together and as close as possible to the audio
amplifier’s output pins. A ferrite bead filter can also
reduce high-frequency interference.
9. For applications where EMC requirements are
extremely stringent or speaker wires are long, use a
second-order LC low-pass filter. Place the filter tightly
together and as close as possible to the audio amplifier’s
output pins. The LC output filter must be designed
specifically for the speaker load since the load impedance
affects the quality factor of the filter.
General Considerations
10. The SGM4703 requires adequate power supply
decoupling to ensure its peak output power, high
efficiency, low distortion, and low EMI emissions. Place
each supply decoupling capacitor as individually close
as possible to AVDD and PVDD pins.
11. Place a small decoupling resistor (10
Ω) between
the system power supply and AVDD to prevent high
frequency Class-D transient spikes from interfering with
the on-chip linear amplifiers.
12. For best noise performance, use differential inputs
from the audio source for SGM4703. In single-ended
input applications, the unused inputs of SGM4703 must
be AC-grounded at the audio source. Also, take care to
match the impedances seen at two differential inputs
closely.
13. The maximum input signal dictates the required
voltage gain to achieve the desired maximum output
power. For best noise performance, consider a voltage
gain as low as possible.
14. Do not alter the logic state of the MODS pin while
the device is in operation. To change the setting of the
pin, the device must be first brought into shutdown
mode by pulling the EN pin low for at least 10ms before
it can be restored to its normal operation.
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