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參數(shù)資料
| 型號： | LM4835MDC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻控制 |
| 英文描述： | 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, UUC |
| 封裝： | DIE |
| 文件頁數(shù)： | 7/26頁 |
| 文件大小： | 858K |
| 代理商： | LM4835MDC |
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Application Information (Continued)
Figure 4 shows the implementation of the LM4835’s head-
phone control function. With no headphones connected to
the headphone jack, the R1-R2 voltage divider sets the
voltage applied to the HP-IN pin (pin 16) at approximately
50mV. This 50mV enables Amp1B and Amp2B, placing the
LM4835 in bridged mode operation. The output coupling
capacitor blocks the amplifier’s half supply DC voltage, pro-
tecting the headphones.
The HP-IN threshold is set at 4V. While the LM4835 operates
in bridged mode, the DC potential across the load is essen-
tially 0V. Therefore, even in an ideal situation, the output
swing cannot cause a false single-ended trigger. Connecting
headphones to the headphone jack disconnects the head-
phone jack contact pin from OUTA and allows R1 to pull the
HP Sense pin up to V
DD. This enables the headphone func-
tion, turns off Amp2A and Amp2B, and mutes the bridged
speaker. The amplifier then drives the headphones, whose
impedance is in parallel with resistor R2 and R3. These
resistors have negligible effect on the LM4835’s output drive
capability since the typical impedance of headphones is
32
.
Figure 4 also shows the suggested headphone jack electri-
cal connections. The jack is designed to mate with a three-
wire plug. The plug’s tip and ring should each carry one of
the two stereo output signals, whereas the sleeve should
carry the ground return. A headphone jack with one control
pin contact is sufficient to drive the HP-IN pin when connect-
ing headphones.
A microprocessor or a switch can replace the headphone
jack contact pin. When a microprocessor or switch applies a
voltage greater than 4V to the HP-IN pin, a bridge-connected
speaker is muted and Amp1A and Amp2A drive a pair of
headphones.
GAIN SELECT FUNCTION (Bass Boost)
The LM4835 features selectable gain, using either internal
and external feedback resistors. Either set of feedback re-
sistors set the gain of the output amplifiers. The voltage
applied to pin 3 (GAIN SELECT pin) controls which gain is
selected. Applying V
DD to the GAIN SELECT pin selects the
external gain mode. Applying 0V to the GAIN SELECT pin
selects the internally set unity gain.
In some cases a designer may want to improve the low
frequency response of the bridged amplifier or incorporate a
bass boost feature. This bass boost can be useful in systems
where speakers are housed in small enclosures. A resistor,
R
LFE, and a capacitor, CLFE, in parallel, can be placed in
series with the feedback resistor of the bridged amplifier as
seen in
Figure 5.
f
C = 1/(2πRLFEC LFE)
(9)
The bridged-amplifier low frequency differential gain is:
A
VD = 2(RF +RLFE)/R i
(10)
Using the component values shown in
Figure 1 (R
F = 20k,
R
LFE = 20k, and CLFE = 0.068F), a first-order, -3dB pole is
created at 120Hz. Assuming R
i = 20k, the low frequency
differential gain is 4. The input (C
i) and output (CO) capacitor
values must be selected for a low frequency response that
covers the range of frequencies affected by the desired
bass-boost operation.
DC VOLUME CONTROL
The LM4835 has an internal stereo volume control whose
setting is a function of the DC voltage applied to the DC VOL
CONTROL pin. The volume control’s voltage input range is
0V to V
DD. The volume range is from 0dB (DC control
voltage = 80% V
DD) to -80dB (DC control voltage = 0V). The
volume remains at 0dB for DC control voltages greater than
80% V
DD. When the MODE input is 0V, the LM4835 oper-
ates at unity gain, bypassing the volume control. A graph
showing a typical volume response versus DC control volt-
age is shown in the Typical Performance Characteristics
section.
Like all volume controls, the LM4835’s internal volume con-
trol is set while listening to an amplified signal that is applied
to an external speaker. The actual voltage applied to the DC
VOL CONTROL pin is a result of the volume a listener
desires. As such, the volume control is designed for use in a
feedback system that includes human ears and preferences.
This feedback system operates quite well without the need
for accurate gain. The user simply sets the volume to the
desired level as determined by their ear, without regard to
the actual DC voltage that produces the volume. Therefore,
the accuracy of the volume control is not critical, as long as
the volume changes monotonically, matches well between
stereo channels, and the step size is small enough to reach
a desired volume that is not too loud or too soft. Since gain
DS100139-11
Figure 5. Low Frequency Enhancement
At low, frequencies C
LFE is a virtual open circuit and at high
frequencies, its nearly zero ohm impedance shorts R
LFE.
The result is increased bridge-amplifier gain at low frequen-
cies. The combination of R
LFE and CLFE form with a -3dB
corner frequency at
LM4835
www.national.com
15
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| LM4835MT | 功能描述:IC AMP AUDIO PWR 2.2W AB 28TSSOP RoHS:否 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機(jī)，2-通道（立體聲） 在某負(fù)載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點(diǎn):I²C，麥克風(fēng)，靜音，短路保護(hù)，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
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