Besides affecting system cost and size, C
參數(shù)資料
型號(hào)： LM4819MX/NOPB
廠商： National Semiconductor
文件頁(yè)數(shù)： 4/27頁(yè)
文件大?。?/td> 0K
描述： IC AMP AUDIO PWR .35W MONO 8SOIC
標(biāo)準(zhǔn)包裝： 1
系列： Boomer®
類型： AB 類
輸出類型： 1-通道（單聲道）
在某負(fù)載時(shí)最大輸出功率 x 通道數(shù)量： 350mW x 1 @ 16 歐姆
電源電壓： 2 V ~ 5.5 V
特點(diǎn)： 消除爆音，差分輸入，關(guān)閉
安裝類型： 表面貼裝
供應(yīng)商設(shè)備封裝： 8-SOIC
封裝/外殼： 8-SOIC（0.154"，3.90mm 寬）
包裝： 剪切帶 (CT)
其它名稱： *LM4819MX/NOPB
LM4819MX/NOPBCT
SNAS133D – FEBRUARY 2001 – REVISED MARCH 2013
Besides affecting system cost and size, Ci has an effect on the LM4819's click and pop performance. When the
supply voltage is first applied, a transient (pop) is created as the charge on the input capacitor changes from zero
to a quiescent state. The magnitude of the pop is directly proportional to the input capacitor's value. Higher value
capacitors need more time to reach a quiescent DC voltage (usually 1/2 VDD) when charged with a fixed current.
The amplifier's output charges the input capacitor through the feedback resistor, RF. Thus, selecting an input
capacitor value that is no higher than necessary to meet the desired -3dB frequency can minimize pops.
As shown in Figure 1, the input resistor (Ri) and the input capacitor, Ci produce a -3dB high pass filter cutoff
frequency that is found using Equation 5.
f-3dB = 1/(2 πRiCi) (Hz)
(5)
As an example when using a speaker with a low frequency limit of 150Hz, Ci, using Equation 5 is 0.063F. The
0.39F Ci shown in Figure 1 allows the LM4819 to drive a high efficiency, full range speaker whose response
extends down to 20Hz.
Besides optimizing the input capacitor value, the bypass capacitor value, CB requires careful consideration. The
bypass capacitor's value is the most critical to minimizing turn-on pops because it determines how fast the
LM4819 turns on. The slower the LM4819's outputs ramp to their quiescent DC voltage (nominally 1/2VDD), the
smaller the turn-on pop. While the device will function properly (no oscillations or motorboating), with CB less
than 1.0F, the device will be much more susceptible to turn-on clicks and pops. Thus, a value of CB equal to or
greater than 1.0F is recommended in all but the most cost sensitive designs.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consideration should be paid to the value of CB, the capacitor
connected to the BYPASS pin. Since CB determines how fast the LM4819 settles to quiescent operation, its
value is critical when minimizing turn-on pops. The slower the LM4819's outputs ramp to their quiescent DC
voltage (nominally 1/2VDD), the smaller the turn-on pop. Choosing CB equal to 1.0F along with a small value of
Ci (in the range of 0.1F to 0.39F) produces a click-less and pop-less shutdown function. As discussed above,
choosing Ci no larger than necessary for the desired bandwidth helps minimize clicks and pops.
Optimizing Click and Pop Reduction Performance
The LM4819 contains circuitry that minimizes turn-on and shutdown transients or "clicks and pops". For this
discussion, turn on refers to either applying the power or supply voltage or when the shutdown mode is
deactivated. While the power supply is ramping to it's final value, the LM4819's internal amplifiers are configured
as unity gain buffers. An internal current source charges the voltage of the bypass capacitor, CB, connected to
the BYPASS pin in a controlled, linear manner. Ideally, the input and outputs track the voltage charging on the
bypass capacitor. The gain of the internal amplifiers remains unity until the bypass capacitor is fully charged to
1/2VDD. As soon as the voltage on the bypass capacitor is stable, the device becomes fully operational. Although
the BYPASS pin current cannot be modified, changing the size of the bypass capacitor, CB, alters the device's
turn-on time and magnitude of "clicks and pops". Increasing the value of CB reduces the magnitude of turn-on
pops. However, this presents a tradeoff: as the size of CB increases, the turn-on time (Ton) increases. There is a
linear relationship between the size of CB and the turn on time. Below are some typical turn-on times for various
values of CB:
CB
TON
0.01F
20ms
0.1F
200ms
0.22F
440ms
0.47F
940ms
1.0F
2S
12
Copyright 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM4819 LM4819MBD
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