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參數(shù)資料
| 型號： | MAX9720 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | 50mW, DirectDrive, Stereo Headphone Amplifier with SmartSense and Shutdown |
| 中文描述： | 50mW、DirectDrive®、立體聲耳機放大器，帶有SmartSense™和關斷 |
| 文件頁數(shù)： | 11/21頁 |
| 文件大?。?/td> | 508K |
| 代理商： | MAX9720 |
DirectDrive
Conventional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage (typical-
ly half the supply) for maximum dynamic range. Large
coupling capacitors are needed to block this DC bias
from the headphone. Without these capacitors, a signifi-
cant amount of DC current flows to the headphone,
resulting in unnecessary power dissipation and possible
damage to both headphone and headphone amplifier.
Maxim
’
s patented DirectDrive architecture uses a
charge pump to create an internal negative supply volt-
age. This allows the MAX9720 output to be biased
about GND, almost doubling dynamic range while
operating from a single supply. With no DC component,
there is no need for the large DC-blocking capacitors.
Instead of two large capacitors (220μF typ), the
MAX9720 charge pump requires only two, small ceram-
ic capacitors (1μF typ), conserving board space,
reducing cost, and improving the frequency response
of the headphone amplifier. See the Output Power vs.
Charge-Pump Capacitance and Load Resistance
graph in the
Typical Operating Characteristics
for
details of the possible capacitor sizes.
Previous attempts to eliminate the output-coupling
capacitors involved biasing the headphone return
(sleeve) to the DC bias voltage of the headphone
amplifiers. This method raised some issues:
The sleeve is typically grounded to the chassis.
Using this biasing approach, the sleeve must be
isolated from system ground, complicating product
design.
During an ESD strike, the amplifier
’
s ESD structures
are the only path to system ground. The amplifier
must be able to withstand the full ESD strike.
When using the headphone jack as a line out to
other equipment, the bias voltage on the sleeve
may conflict with the ground potential from other
equipment, resulting in large ground-loop current
and possible damage to the amplifiers.
When using a combination microphone and speak-
er headset (in a cell phone or PDA application), the
microphone typically requires a GND return. Any
DC bias on the sleeve conflicts with the microphone
requirements (Figure 2).
Low-Frequency Response
In addition to the cost and size disadvantages, the DC-
blocking capacitors limit the low-frequency response of
the amplifier and distort the audio signal:
The impedance of the headphone load and the DC-
blocking capacitor form a highpass filter with the
-3dB point determined by:
where R
L
is the impedance of the headphone and
C
OUT
is the value of the DC-blocking capacitor.
The highpass filter is required by conventional single-
ended, single-supply headphone amplifiers to block
the midrail DC component of the audio signal from the
headphones. Depending on the -3dB point, the filter
can attenuate low-frequency signals within the audio
band. Larger values of C
OUT
reduce the attenuation,
but are physically larger, more expensive capacitors.
Figure 3 shows the relationship between the size of
C
OUT
and the resulting low-frequency attenuation. Note
that the -3dB point for a 16
headphone with a 100μF
blocking capacitor is 100Hz, well within the audio
band.
f
R C
π
dB
=
3
1
2
M
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
______________________________________________________________________________________
11
+V
DD
-V
DD
GND
V
OUT
CONVENTIONAL DRIVER-BIASING SCHEME
DirectDrive BIASING SCHEME
V
DD
/2
V
DD
GND
V
OUT
Figure 1. Conventional Amplifier Output Waveform vs.
MAX9720 Output Waveform
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| MAX97200AEVKIT+ | 功能描述:音頻 IC 開發(fā)工具 MAX97200A Eval Kit RoHS:否 制造商:Texas Instruments 產(chǎn)品:Evaluation Kits 類型:Audio Amplifiers 工具用于評估:TAS5614L 工作電源電壓:12 V to 38 V |
| MAX97200AEWC+ | 制造商:Maxim Integrated Products 功能描述:HIGH EFFICIENCY HEADPHONE AMPLIFIER - Rail/Tube |
| MAX97200AEWC+T | 功能描述:音頻放大器 Class H DirectDrive Headphone Amplifier RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| MAX97200BEWC+T | 功能描述:音頻放大器 Class H DirectDrive Headphone Amplifier RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| MAX9720AEBE | 制造商:Maxim Integrated Products 功能描述:50MW, DIRECTDRIVE, STEREO HEADPHONE AMPLIFIER - Rail/Tube |
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