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参数资料
| 型号： | LM4840LQ/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频控制 |
| 英文描述： | 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, QCC28 |
| 封装： | LLP-28 |
| 文件页数： | 2/22页 |
| 文件大小： | 829K |
| 代理商： | LM4840LQ/NOPB |
Application Information
DIGITAL VOLUME CONTROL
The LM4840 features a digital volume control which consists
of the CLOCK, UP, and DOWN pins. An external clock may
be fed to the CLOCK pin, or, by connecting a capacitor from
the CLOCK pin to ground, the internal clock may be used.
The internal clock frequency with respect to this capacitor
value is determined from the following formula:
f
CLK = (7.338 x 10
-7 )/C
When using an external clock, the clock is buffered and the
internal clock frequency is that of the external clock divided
by 2. Also, the maximum frequency should be kept below
100kHz.
Volume changes are then effected by toggling either the UP
or DOWN pins with a logic high. After a period of 4 clock
pulses with either the UP or DOWN pins held high, the
volume will change to the next specified step, either up or
down. Volume levels for each step vary and are specified in
Table 2. If either the UP or DOWN pin remains high after the
first volume transition the volume will change again, but this
time after 40 clock pulses. The next transition occurs at 20
clock pulses, then 12, then 8, and from then on 4 clock
pulses for each volume transtition. This cycle is shown in the
timing diagram shown in Figure 3. Releasing the held UP or
DOWN pin to ground at any time re-starts the cycle. This is
intended to provide the user with a volume control that
pauses briefly after initial application, then slowly increases
the rate of volume change as it is continuously applied.
If both the UP and DOWN pins are held high, no volume
change will occur. Trigger points for the UP and DOWN pins
are at 60% of V
DD minimum for a logic high, and 20% of VDD
maximum for a logic low. It is recommended, however, to
toggle UP and DOWN between V
DD and GND for best
performance. When using an external clock, clock pulses
should be a minimum 0f 3V for a high and maximum of 0.9V
for a low when using a 5V supply. Again, pulsing an external
clock from V
DD to GND ensures reliable performance. Fol-
lowing these guidelines the volume may then be changed
with a microcontroller or manually using switches.
MEMORY FUNCTION
The LM4840 features a volume memory that saves the last
volume setting when power is turned off. This requires that
an auxiliary power source be connected to V
AUX through a
diode as shown in Figure 1. Connecting the circuit as shown
also provides that power to the V
AUX pin is being drawn from
V
DD when VDD is on and is greater than VAUX.VAUX must be
at a voltage of 2.3V or greater to maintain volume memory
when V
DD is absent. This feature is intended for such appli-
cations as laptop computers, where V
DD is the system power
and V
AUX is connected to the real time clock battery. The
default volume setting for the LM4840 is -10dB in BTL mode,
and -16dB in single-ended mode. This default setting is only
achieved on power up when both V
DD and VAUX had both
been turned off, and the circuit had sufficient time to dis-
charge (<500ms depending on capacitor value at V
AUX).
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 LM4840 eliminates these coupling capacitors. Amp2A is
internally configured to apply V
DD/2 to a stereo headphone
jack’s sleeve. This voltage matches the quiescent voltage
present on the Amp1A and Amp1B outputs that drive the
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
LM4840’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 LM4840 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 LM4840 and the external equipment. For more
information, see the section titled ’Single-Ended Output
Power Performance and Measurement Considerations’.
EXPOSED-DAP MOUNTING CONSIDERATIONS
The LM4840’s exposed-DAP (die attach paddle) packages
(MH, LQ) provide 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 2W at
≤ 1% THD with a 4 load. This high power
is achieved through careful consideration of necessary ther-
mal design. Failing to optimize thermal design may compro-
mise the LM4840’s high power performance and activate
unwanted, though necessary, thermal shutdown protection.
The MH and LQ packages must have their exposed DAPs
soldered to a grounded copper pad on the PCB. The DAP’s
PCB copper pad is connected to a large plane of continuous
unbroken copper. This plane forms a thermal mass and heat
sink and radiation area. Place the heat sink area on either
outside plane in the case of a two-sided PCB, or on an inner
layer of a board with more than two layers. Connect the DAP
copper pad to the inner layer or backside copper heat sink
area with 32(4x8) (MH ) or 6(3x2) (LQ) vias. The via diam-
eter should be 0.012in–0.013in with a 1.27mm pitch. Ensure
efficient thermal conductivity by plating-through and solder-
filling the vias.
Best thermal performance is achieved with the largest prac-
tical copper heat sink area. If the heatsink and amplifier
share the same PCB layer, a nominal 2.5in2 (min) area is
necessary for 5V operation with a 4
load. Heatsink areas
not placed on the same PCB layer as the should be 5in
2
(min) for the same supply voltage and load resistance. The
last two area recommendations apply for 25C ambient tem-
perature. Increase the area to compensate for ambient tem-
peratures above 25C. In systems using cooling fans, the
LM4840MH can take advantage of forced air cooling. With
an air flow rate of 450 linear-feet per minute and a 2.5in
2
exposed copper or 5.0in
2 inner layer copper plane heatsink,
the LM4840MH can continuously drive a 3
load to full
power. The LM4840LQ achieves the same output power
LM4840
www.national.com
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM4840MH | 制造商:Texas Instruments 功能描述:AMP AUDIO STEREO 2W SMD TSSOP28 |
| LM4840MH/NOPB | 功能描述:IC AMP AUDIO PWR 2.2W AB 28TSSOP RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Boomer® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:DirectDrive® 类型:H 类 输出类型:耳机，2-通道（立体声） 在某负载时最大输出功率 x 通道数量:35mW x 2 @ 16 欧姆 电源电压:1.62 V ~ 1.98 V 特点:I²C，麦克风，静音，短路保护，音量控制 安装类型:表面贴装 供应商设备封装:25-WLP（2.09x2.09） 封装/外壳:25-WFBGA，WLCSP 包装:带卷 (TR) |
| LM4840MT | 制造商:Texas Instruments 功能描述:AMP AUDIO STEREO 2W SMD TSSOP28 |
| LM4840MT/NOPB | 功能描述:IC AMP AUDIO PWR 2.2W AB 28TSSOP RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Boomer® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:DirectDrive® 类型:H 类 输出类型:耳机，2-通道（立体声） 在某负载时最大输出功率 x 通道数量:35mW x 2 @ 16 欧姆 电源电压:1.62 V ~ 1.98 V 特点:I²C，麦克风，静音，短路保护，音量控制 安装类型:表面贴装 供应商设备封装:25-WLP（2.09x2.09） 封装/外壳:25-WFBGA，WLCSP 包装:带卷 (TR) |
| LM4841 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Stereo 2W Amplifiers with DC Volume Control, Transient Free Outputs, and Cap-less Headphone Drive |
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