High-Power Stereo Class-D Audio Power Amplifier
SGM4703 with Adjustable Power Limit and Automatic Level Control
18
DECEMBER 2022
SG Micro Corp
www.sg-micro.com
APPLICATION INFORMATION
The SGM4703 is a high-power, high efficiency, stereo
Class-D audio power amplifier with adjustable power
limit (APL) and automatic level control (ALC). It
operates with a wide range of supply voltages from 5V
to 26V. With 24V supply voltage, it can deliver 2 × 40W
peak output power for a pair of 8Ω speakers with 10%
THD+N.
The high efficiency of SGM4703 extends battery life in
playing music and allows it to deliver an output power
of 2 × 20W without the need for a bulky heat sink on a
two-layer system board. Its high PSRR and low EMI
emission reduce system design and manufacturing
complexities, as well as thus lower system cost.
The SGM4703 features APL and ALC. The APL limits
peak audio outputs to a user-defined value to protect
audio speakers from excessive power dissipation and
over-load. The APL and ALC adjust the voltage gain of
the audio amplifiers in response to over-limit audio
inputs, eliminating output clipping distortion while
maintaining a maximally allowed dynamic range of
audio outputs. The limiting voltage of APL and ALC can
be either the supply voltage or a user-defined value.
The SGM4703 can be configured into driving either a
pair of speakers in Bridge-Tied-Load (BTL)
configuration for stereo applications or a single speaker
in Parallel BTL (PBTL) configuration for mono
applications. In PBTL configuration, with 15V supply
voltage, it can deliver into a 3Ω speaker an output
power of 33W with 1% THD+N, or an ALC output power
of 30W with THD+N less than 0.5%.
The SGM4703 features two PWM modulation schemes
for use in Class-D audio amplifiers: Dual-Side-
Modulation (DSM) and Single-Side-Modulation (SSM),
allowing for system optimization for higher efficiency or
lower THD.
The SGM4703 includes comprehensive protection
modes against various operating faults including
under-voltage, over-voltage, over-current, over-
temperature, and DC-detect for safe and reliable
operation.
Operating Mode Control
The SGM4703 features APL and ALC modes of
operation. In APL mode, peak audio outputs are
clamped (hard-limited) to a voltage level defined by the
PLIMIT pin, protecting audio speakers from excessive
power dissipation and over-load.
As described in Table 1, depending upon the pin
voltage at PLIMIT and the pin configuration at ALC, the
SGM4703 can be configured into one of four operating
modes: Mute, APL, ALC, and Traditional. In SGM4703,
the pin voltage at PLIMIT, V
PLIMIT
, defines the limiting
voltage of audio outputs for both APL and ALC modes.
If V
PLIMIT
is set less than 0.3V, the device operates in
mute mode regardless of the pin configuration at ALC.
If V
PLIMIT
is set higher than 4.5V with the ALC pin
unconnected, the device operates in a traditional
Class-D mode without APL or ALC. In this mode, the
output clipping distortion will occur as peak output
voltages reach to the supply voltage PVDD.
If V
PLIMIT
is set in the range from 0.7V to 3.5V with the
ALC pin connected to ground through an external
resistor of 0kΩ, 68kΩ or 300kΩ, the device operates in
APL mode. The audio outputs in APL mode are limited
to a value approximately equal to (6 × V
PLIMIT
).
If V
PLIMIT
is set higher than 4.5V with the ALC pin
connected to ground through an external resistor of
0kΩ, 68kΩ, or 300kΩ, the device operates in ALC mode
and the limiting voltage of audio outputs is internally set
at the supply voltage. Thus, the peak voltage of audio
outputs is limited to a value that is substantially close to
PVDD.
Table 1. Operating Mode Control
V
PLIMIT
R
ALC
Mode Description
V
PLIMIT
< 0.3V X Mute Audio outputs shorted to PGND.
V
PLIMIT
< 4.5V
Open
X Not applicable.
V
PLIMIT
> 4.5V Traditional No APL and No ALC.
0.7V < V
PLIMIT
< 3.5V
0kΩ, 68kΩ or 300kΩ
to GND
APL Audio outputs limited to a value defined by V
PLIMIT
.
V
PLIMIT
> 4.5V ALC Audio outputs limited to the supply voltage PVDD.
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