 |
công cụ tìm kiếm bảng dữ liệu linh kiện điện tử |
|
|
công cụ tìm kiếm bảng dữ liệu linh kiện điện tử |
|
LM4816MT bảng dữ liệu(PDF) 10 Page - National Semiconductor (TI) |
|
|
||||||||||||||||||||||||||||||
LM4816MT bảng dữ liệu(HTML) 10 Page - National Semiconductor (TI) |
|
|
10 / 13 page  Application Information (Continued) presence does not eliminate the need for a local 1.0µF tantalum bypass capacitance connected between the LM4816’s supply pins and ground. Do not substitute a ce- ramic capacitor for the tantalum. Doing so may cause oscil- lation in the output signal. Keep the length of leads and traces that connect capacitors between the LM4816’s power supply pin and ground as short as possible. Connecting a 1µF capacitor, C B, between the BYPASS pin and ground improves the internal bias voltage’s stability and improves the amplifier’s PSRR. The PSRR improvements increase as the bypass pin capacitor value increases. Too large, how- ever, increases turn-on time and can compromise amplifier’s click and pop performance. The selection of bypass capaci- tor values, especially C B, depends on desired PSRR require- ments, click and pop performance (as explained in the sec- tion, Proper Selection of External Components), system cost, and size constraints. MICRO-POWER SHUTDOWN The voltage applied to the SHUTDOWN pin controls the LM4816’s shutdown function. Activate micro-power shut- down by applying V DD to the SHUTDOWN pin. When active, the LM4816’s micro-power shutdown feature turns off the amplifier’s bias circuitry, reducing the supply current. The logic threshold is typically V DD/2. The low 0.6µA typical shutdown current is achieved by applying a voltage that is as near as V DD as possible to the SHUTDOWN pin. A voltage thrat is less than V DD may increase the shutdown current. There are a few ways to control the micro-power shutdown. These include using a single-pole, single-throw switch, a microprocessor, or a microcontroller. When using a switch, connect an external 10k Ω pull-up resistor between the SHUTDOWN pin and V DD. Connect the switch between the SHUTDOWN pin and ground. Select normal amplifier opera- tion by closing the switch. Opening the switch connects the SHUTDOWN pin to V DD through the pull-up resistor, activat- ing micro-power shutdown. The switch and resistor guaran- tee that the SHUTDOWN pin will not float. This prevents unwanted state changes. In a system with a microprocessor or a microcontroller, use a digital output to apply the control voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin with active circuitry eliminates the pull up resistor. TABLE 1. LOGIC LEVEL TRUTH TABLE FOR SHUT- DOWN OPERATION SHUTDOWN OPERATIONAL MODE Low Full power, stereo BTL amplifiers High Micro-power Shutdown SELECTING PROPER EXTERNAL COMPONENTS Optimizing the LM4816’s performance requires properly se- lecting external components. Though the LM4816 operates well when using external components with wide tolerances, best performance is achieved by optimizing component val- ues. The LM4816 is unity-gain stable, giving a designer maximum design flexibility. The gain should be set to no more than a given application requires. This allows the amplifier to achieve minimum THD+N and maximum signal-to-noise ra- tio. These parameters are compromised as the closed-loop gain increases. However, low gain demands input signals with greater voltage swings to achieve maximum output power. Fortunately, many signal sources such as audio CO- DECs have outputs of 1V RMS (2.83VP-P). Please refer to the Audio Power Amplifier Design section for more informa- tion on selecting the proper gain. Input Capacitor Value Selection Amplifying the lowest audio frequencies requires high value input coupling capacitor (C i in Figure 1). A high value capaci- tor can be expensive and may compromise space efficiency in portable designs. In many cases, however, the speakers used in portable systems, whether internal or external, have little ability to reproduce signals below 150Hz. Applications using speakers with this limited frequency response reap little improvement by using large input capacitor. Besides effecting system cost and size, C i has an affect on the LM4816’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 quies- cent state. The magnitude of the pop is directly proportional to the input capacitor’s size. Higher value capacitors need more time to reach a quiescent DC voltage (usually V DD/2) when charged with a fixed current. The amplifier’s output charges the input capacitor through the feedback resistor, R f. Thus, pops can be minimized by selecting an input capacitor value that is no higher than necessary to meet the desired -3dB frequency. A shown in Figure 1, the input resistor (R I) and the input capacitor, C I produce a −3dB high pass filter cutoff frequency that is found using Equation (7). (7) As an example when using a speaker with a low frequency limit of 150Hz, C I, using Equation (4), is 0.063µF. The 1.0µF C I shown in Figure 1 allows the LM4816 to drive high effi- ciency, full range speaker whose response extends below 30Hz. Bypass Capacitor Value Selection Besides minimizing the input capacitor size, careful consid- eration should be paid to value of C B, the capacitor con- nected to the BYPASS pin. Since C B determines how fast the LM4816 settles to quiescent operation, its value is critical when minimizing turn−on pops. The slower the LM4816’s outputs ramp to their quiescent DC voltage (nominally 1/2 V DD), the smaller the turn−on pop. Choosing CB equal to 1.0µF along with a small value of C i (in the range of 0.1µF to 0.39µF), produces a click-less and pop-less shutdown func- tion. As discussed above, choosing C i no larger than neces- sary for the desired bandwidth helps minimize clicks and pops. OPTIMIZING CLICK AND POP REDUCTION PERFORMANCE The LM4816 contains circuitry to minimize turn-on and shut- down transients or "clicks and pop". For this discussion, turn-on refers to either applying the power supply voltage or when the shutdown mode is deactivated. While the power supply is ramping to its final value, the LM4816’s internal amplifiers are configured as unity gain buffers. An internal current source changes the voltage of the BYPASS pin in a controlled, linear manner. Ideally, the input and outputs track www.national.com 10 |
Số phần tương tự - LM4816MT |
|
Mô tả tương tự - LM4816MT |
|
|
|
Link URL |
| Chính sách bảo mật |
| ALLDATASHEET.VN |
| Cho đến nay ALLDATASHEET có giúp ích cho doanh nghiệp của bạn hay không? [ DONATE ] |
Alldatasheet là | Quảng cáo | Liên lạc với chúng tôi | Chính sách bảo mật | Trao đổi link | Tìm kiếm theo nhà sản xuất All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
Vietnamese ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
