參數(shù)資料
型號(hào)： LM4868MT/NOPB
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類(lèi)： 音頻／視頻放大
英文描述： 1.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20
封裝： 4.40 MM, PLASTIC, TSSOP-20
文件頁(yè)數(shù)： 4/28頁(yè)
文件大?。?/td> 792K
代理商： LM4868MT/NOPB
Application Information (Continued)
headphones. The headphones 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
LM4868’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 LM4868 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 LM4868 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 LM4868 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 (>25mV
RMS, typ) to mask any remaining transient that
may occur.
Figure 2 shows the LM4868’s lack of transients in the differ-
ential signal (Trace B) across a BTL 8
load. The LM4868’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 3 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 is seen.
USING THE LM4868 TO UPGRADE LM4863 AND LM4873
DESIGNS
The
LM4868’s
noise-free
operation
plus
coupling-capacitorless headphone operation and functional
compatibility with the LM4873 and the LM4863 simplifies
upgrading systems using these parts. Upgrading older de-
signs that use either the LM4863 or the LM4873 is easy.
Simply remove and short the coupling capacitors located
between the LM4873’s or LM4863’s Amp1A and Amp1B
outputs and the headphone connections. Also remove the
1k
resistor between each headphone connection and
ground. Finally, remove any resistors connected to the
HP-IN pin (typically two 100k
resistors). Connect the HP-IN
pin directly to the headphone jack control pin as shown in
The LM4868’s pin configuration simplifies the process of
upgrading systems that use the LM4863. Except for its four
MUX function pins, the LM4868’s pin configuration matches
the LM4863’s pin configuration. If the LM4868’s MUX func-
tionality is not needed when replacing an LM4863, connect
the MUX CTRL pin to either V
DD or ground. To ensure
correct amplifier operation, unused MUX inputs should be
tied to GND. As shown in Table 1, grounding the MUX CTRL
pin selects stereo input 1 (IN A1 and IN B1), whereas
applying V
DD to the MUX CTRL pin selects stereo input 2
(IN A2 and IN B2).
The LM4868’s unique headphone sense circuit requires a
dual switch headphone jack. Replace the four-terminal head-
phone jack used with the LM4863 and LM4873 with the
five-terminal headphone jack, such as the Switchcraft
35RAPC4BH3, shown in Figure 4. Connect the +OUT A
(Amp2A) pin to the five-terminal headphone jack’s sleeve
pin.
20026756
FIGURE 2. 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.
20026757
FIGURE 3. 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.
LM4868
www.national.com
12
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LM4869MH/NOPB 功能描述:IC AMP AUDIO PWR 2.6W AB 20TSSOP RoHS:是 類(lèi)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(lèi)型:H 類(lèi) 輸出類(lèi)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(lèi)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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