參數(shù)資料
型號(hào)： LM4842MHX/NOPB
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 音頻控制
英文描述： 2 CHANNEL(S), TONE CONTROL CIRCUIT, PDSO28
封裝： TSSOP-28
文件頁(yè)數(shù)： 9/31頁(yè)
文件大?。?/td> 1306K
代理商： LM4842MHX/NOPB
Application Information
ELIMINATING OUTPUT COUPLING CAPACITORS
Typical single-supply audio amplifiers that can switch be-
tween
driving
bridge-tied-load
(BTL)
speakers
and
single-ended (SE) headphones use a coupling capacitor on
each SE output. This capacitor blocks the half-supply volt-
age to which the output amplifiers are typically biased and
couples the audio signal to the headphones. The signal
return to circuit ground is through the headphone jack’s
sleeve.
The LM4842 eliminates these coupling capacitors. Amplifi-
erA+ (pin 28 on MT/MH) is internally configured to apply
V
DD/2 to a stereo headphone jack’s sleeve. This voltage
matches the quiescent voltage present on the AmpAout- and
AmpBout- outputs that drive the headphones. The head-
phones
operate
in
a
manner
very
similar
to
a
bridge-tied-load (BTL). The same DC voltage is applied to
both headphone speaker terminals. This results in no net DC
current flow through the speaker. AC current flows through a
headphone speaker as an audio signal’s output amplitude
increases on the speaker’s terminal.
When operating as a headphone amplifier, the headphone
jack sleeve is not connected to circuit ground. Using the
headphone output jack as a line-level output will place the
LM4842’s one-half supply voltage on a plug’s sleeve con-
nection.
Driving
a
portable
notebook
computer
or
audio-visual display equipment is possible. This presents no
difficulty when the external equipment uses capacitively
coupled inputs. For the very small minority of equipment that
is DC-coupled, the LM4842 monitors the current supplied by
the amplifier that drives the headphone jack’s sleeve. If this
current exceeds 500mA
PK, the amplifier is shutdown, pro-
tecting the LM4842 and the external equipment. For more
information, see the section titled ’Single-Ended Output
Power Performance and Measurement Considerations’.
OUTPUT TRANSIENT (’POPS AND CLICKS’)
ELIMINATED
The LM4842 contains advanced circuitry that eliminates out-
put transients (’pop and click’). This circuitry prevents all
traces of transients when the supply voltage is first applied,
when the part resumes operation after shutdown, or when
switching between BTL speakers and SE headphones. Two
circuits combine to eliminate pop and click. One circuit
mutes the output when switching between speaker loads.
Another circuit monitors the input signal. It maintains the
muted condition until there is sufficient input signal magni-
tude (>22mV
RMS, typ) to mask any remaining transient that
may occur. (See Turn On Characteristics).
Figure 3 shows the LM4842’s lack of transients in the differ-
ential signal (Trace B) across a BTL 8
load. The LM4842’s
active-high SHUTDOWN pin is driven by the logic signal
shown in Trace A. Trace C is the VOUT- output signal and
trace D is the VOUT+ output signal. The shutdown signal
frequency is 1Hz with a 50% duty cycle. Figure 4 is gener-
ated with the same conditions except that the output drives a
32
single-ended (SE) load. Again, no trace of output tran-
sients on Trace B can be observed.
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATIONS
The LM4842’s exposed-DAP (die attach paddle) package
(MH,LQ) provides a low thermal resistance between the die
and the PCB to which the part is mounted and soldered. This
allows rapid heat transfer from the die to the surrounding
PCB copper traces, ground plane and, finally, surrounding
air. The result is a low voltage audio power amplifier that
produces 2.1W at
≤ 1% THD with a 4 load. This high power
is achieved through careful consideration of necessary ther-
20028198
FIGURE 3. Differential output signal (Trace B) is devoid
of transients. The SHUTDOWN pin is driven by a
shutdown signal (Trace A). The inverting output (Trace
C) and the non-inverting output (Trace D) are applied
across an 8
BTL load.
20028199
FIGURE 4. Single-ended output signal (Trace B) is
devoid of transients. The SHUTDOWN pin is driven by
a shutdown signal (Trace A). The inverting output
(Trace C) and the V
BYPASS output (Trace D) are applied
across a 32
BTL load.
LM4842
www.national.com
17
相關(guān)PDF資料
PDF描述
LM4842MTX/NOPB 2 CHANNEL(S), TONE CONTROL CIRCUIT, PDSO28
LM4843MH/NOPB 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, PDSO20
LM4843MHX/NOPB 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, PDSO20
LM4850MM/NOPB 0.3 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10
LM4850MT/NOPB 0.3 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO14
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM4842MT 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 2W Amplifiers with DC Volume Control Transient Free Outputs, and Cap-less Headphone Drive
LM4842MT/NOPB 功能描述:IC AMP AUDIO PWR 2.2W AB 28TSSOP RoHS:是 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(shí)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)
LM4843 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 2W Audio Power Amplifiers with DC Volume Control
LM4843MH 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 2W Audio Power Amplifiers with DC Volume Control
LM4843MHX 功能描述:IC AMP AUDIO PWR 2.2W AB 20TSSOP RoHS:是 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(shí)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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