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| 型號： | LM4891IBP/NOPB |
| 廠商： | National Semiconductor |
| 文件頁數(shù)： | 5/21頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC AMP AUDIO PWR 1W MONO 8USMD |
| 標準包裝： | 1 |
| 系列： | Boomer® |
| 類型： | AB 類 |
| 輸出類型： | 1-通道（單聲道） |
| 在某負載時最大輸出功率 x 通道數(shù)量： | 1W x 1 @ 8 歐姆 |
| 電源電壓： | 2.2 V ~ 5.5 V |
| 特點： | 消除爆音，關機，熱保護 |
| 安裝類型： | 表面貼裝 |
| 供應商設備封裝： | 8-uSMD |
| 封裝/外殼： | 8-VFBGA |
| 包裝： | 剪切帶 (CT) |
| 其它名稱： | *LM4891IBP *LM4891IBP/NOPB LM4891IBPCT |
OBSOLETE
SNAS122E – MAY 2001 – REVISED APRIL 2013
POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection. The capacitor location on both the bypass and power supply pins should be as close to the device as
possible. Typical applications employ a 5V regulator with 10 F tantalum or electrolytic capacitor and a ceramic
bypass capacitor which aid in supply stability. This does not eliminate the need for bypassing the supply nodes of
the LM4891. The selection of a bypass capacitor, especially CB, is dependent upon PSRR requirements, click
and pop performance (as explained in the section, PROPER SELECTION OF EXTERNAL COMPONENTS),
system cost, and size constraints.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the LM4891 contains a shutdown pin to externally turn off
the amplifier's bias circuitry. This shutdown feature turns the amplifier off when a logic high is placed on the
shutdown pin. By switching the shutdown pin to VDD, the LM4891 supply current draw will be minimized in idle
mode. While the device will be disabled with shutdown pin voltages more than 1.0VDC, the idle current may be
greater than the typical value of 0.1A. (Idle current is measured with the shutdown pin tied to VDD).
In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry to
provide a quick, smooth transition into shutdown. Another solution is to use a single-pole, single-throw switch in
conjunction with an external pull-up resistor. When the switch is closed, the shutdown pin is connected to ground
which enables the amplifier. If the switch is open, then the external pull-up resistor to VDD will disable the
LM4891. This scheme guarantees that the shutdown pin will not float thus preventing unwanted state changes.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications using integrated power amplifiers is critical to optimize
device and system performance. While the LM4891 is tolerant of external component combinations,
consideration to component values must be used to maximize overall system quality.
The LM4891 is unity-gain stable which gives the designer maximum system flexibility. The LM4891 should be
used in low gain configurations to minimize THD+N values, and maximize the signal to noise ratio. Low gain
configurations require large input signals to obtain a given output power. Input signals equal to or greater than 1
Vrms are available from sources such as audio codecs. Please refer to the section, AUDIO POWER AMPLIFIER
DESIGN, for a more complete explanation of proper gain selection.
Besides gain, one of the major considerations is the closed-loop bandwidth of the amplifier. To a large extent, the
bandwidth is dictated by the choice of external components shown in Figure 1. The input coupling capacitor, Ci,
forms a first order high pass filter which limits low frequency response. This value should be chosen based on
needed frequency response for a few distinct reasons.
SELECTION OF INPUT CAPACITOR SIZE
Large input capacitors are both expensive and space hungry for portable designs. Clearly, a certain sized
capacitor is needed to couple in low frequencies without severe attenuation. But in many cases the speakers
used in portable systems, whether internal or external, have little ability to reproduce signals below 100 Hz to
150 Hz. Thus, using a large input capacitor may not increase actual system performance.
In addition to system cost and size, click and pop performance is effected by the size of the input coupling
capacitor, Ci. A larger input coupling capacitor requires more charge to reach its quiescent DC voltage (nominally
1/2 VDD). This charge comes from the output via the feedback and is apt to create pops upon device enable.
Thus, by minimizing the capacitor size based on necessary low frequency response, turn-on pops can be
minimized.
Besides minimizing the input capacitor size, careful consideration should be paid to the bypass capacitor value.
Bypass capacitor, CB, is the most critical component to minimize turn-on pops since it determines how fast the
LM4891 turns on. The slower the LM4891's outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the
smaller the turn-on pop. Choosing CB equal to 1.0 F along with a small value of Ci (in the range of 0.1 F to
0.39 F), should produce a virtually clickless and popless shutdown function. While the device will function
properly, (no oscillations or motorboating), with CB equal to 0.1 F, the device will be much more susceptible to
turn-on clicks and pops. Thus, a value of CB equal to 1.0 F is recommended in all but the most cost sensitive
designs.
Copyright 2001–2013, Texas Instruments Incorporated
13
Product Folder Links: LM4891
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4891IBPX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1 Watt Audio Power Amplifier |
| LM4891ITP/NOPB | 功能描述:IC AMP AUDIO PWR 1W MONO 8USMD RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機，2-通道（立體聲） 在某負載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4891LD | 功能描述:IC AMP AUDIO PWR 1W MONO 10LLP RoHS:否 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機，2-通道（立體聲） 在某負載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4891LDX | 功能描述:IC AMP AUDIO PWR 1W MONO 10LLP RoHS:否 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機，2-通道（立體聲） 在某負載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4891M | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1 Watt Audio Power Amplifier |
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