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參數(shù)資料
| 型號： | EVAL-SSM2375Z |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 5/16頁 |
| 文件大?。?/td> | 0K |
| 描述： | BOARD EVALUATION FOR SSM2375 |
| 標(biāo)準包裝： | 1 |
| 放大器類型： | D 類 |
| 輸出類型： | 1-通道（單聲道） |
| 在某負載時最大輸出功率 x 通道數(shù)量： | 3.7W x 1 @ 3 歐姆 |
| 電源電壓： | 2.5 V ~ 5.5 V |
| 工作溫度： | -40°C ~ 85°C |
| 板類型： | 完全填充 |
| 已用 IC / 零件： | SSM2375 |
| 已供物品： | 板 |
Data Sheet
SSM2375
Rev. A | Page 13 of 16
THEORY OF OPERATION
OVERVIEW
The SSM2375 mono Class-D audio amplifier features a filterless
modulation scheme that greatly reduces the external component
count, conserving board space and, thus, reducing systems cost.
The SSM2375 does not require an output filter but, instead, relies
on the inherent inductance of the speaker coil and the natural
filtering of the speaker and human ear to fully recover the audio
component of the switching output.
Most Class-D amplifiers use some variation of pulse-width
modulation (PWM), but the SSM2375 uses Σ-Δ modulation to
determine the switching pattern of the output devices, resulting
in a number of important benefits.
Σ-Δ modulators do not produce a sharp peak with many
harmonics in the AM frequency band, as pulse-width
modulators often do.
Σ-Δ modulation provides the benefits of reducing the
amplitude of spectral components at high frequencies,
that is, reducing EMI emissions that might otherwise be
radiated by speakers and long cable traces.
Due to the inherent spread-spectrum nature of Σ-Δ modu-
lation, the need for oscillator synchronization is eliminated
for designs that incorporate multiple SSM2375 amplifiers.
The SSM2375 also integrates overcurrent and overtemperature
protection.
GAIN SELECTION
The preset gain of the SSM2375 can be set from 0 dB to 12 dB
in 3 dB steps with one external resistor (optional). The external
resistor is used to select the 9 dB or 12 dB gain setting, as shown
To avoid excessive induced noise at high output power, observe
caution under the following conditions: GAIN pin is configured
to the 3 dB gain setting (open) and using both low impedance
(less than 3 + 10 μH) loading and configured for low emissions
mode (EDGE = VDD). To safeguard against the potential induced
noise at high power levels in this configuration, connect a capacitor
from GAIN to GND with a value ranging from 2.2 μF to 4.7 μF.
Alternatively, apply a fixed voltage of VDD/2 to the GAIN pin
to stabilize the gain setting operation under the low impedance/
high power condition stated above.
Table 5. Gain Function Descriptions
Gain Setting (dB)
GAIN Pin Configuration
12
Tie to VDD through 47 k resistor
9
Tie to GND through 47 k resistor
6
Tie to VDD
Open
0
Tie to GND
1
See the Gain Selection section for more information on avoiding excessive
induced noise.
POP-AND-CLICK SUPPRESSION
Voltage transients at the output of audio amplifiers can occur
when shutdown is activated or deactivated. Voltage transients as
low as 10 mV can be heard as an audio pop in a low sensitivity
handset speaker. Clicks and pops can also be classified as undesir-
able audible transients generated by the amplifier system and,
therefore, as not coming from the system input signal.
The SSM2375 has a pop-and-click suppression architecture that
reduces these output transients, resulting in noiseless activation
and deactivation from the SD control pin while operating in a
typical audio configuration.
EMI NOISE
The SSM2375 uses a proprietary modulation and spread-spectrum
technology to minimize EMI emissions from the device. For
applications that have difficulty passing FCC Class B emission
tests, the SSM2375 includes a modulation select pin (ultralow
EMI emissions mode) that significantly reduces the radiated
emissions at the Class-D outputs, particularly above 100 MHz.
EMI emission tests on the SSM2375 were performed in a certified
FCC Class B laboratory in low emissions mode (EDGE = VDD).
With a pink noise source, an 8 speaker load, and a 5 V supply,
the SSM2375 was able to pass FCC Class B limits with 50 cm,
unshielded twisted pair speaker cable. Note that reducing the
power supply voltage greatly reduces radiated emissions.
OUTPUT MODULATION DESCRIPTION
The SSM2375 uses three-level, Σ-Δ output modulation. Each
output can swing from GND to VDD and vice versa. Ideally, when
no input signal is present, the output differential voltage is 0 V
because there is no need to generate a pulse. In a real-world
situation, there are always noise sources present.
Due to this constant presence of noise, a differential pulse is
generated, when required, in response to this stimulus. A small
amount of current flows into the inductive load when the differ-
ential pulse is generated.
Most of the time, however, the output differential voltage is 0 V,
due to the Analog Devices, Inc., three-level, Σ-Δ output modula-
tion. This feature ensures that the current flowing through the
inductive load is small.
When the user wants to send an input signal, an output pulse
is generated to follow the input voltage. The differential pulse
density is increased by raising the input signal level. Figure 35
depicts three-level, Σ-Δ output modulation with and without
input stimulus.
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