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LM48510 bảng dữ liệu(PDF) 11 Page - Texas Instruments |
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LM48510 bảng dữ liệu(HTML) 11 Page - Texas Instruments |
11 / 30 page LM48510 www.ti.com SNAS275D – NOVEMBER 2006 – REVISED OCTOBER 2007 AMPLIFIER DISSIPATION In general terms, efficiency is considered to be the ratio of useful work output divided by the total energy required to produce it with the difference being the power dissipated, typically, in the IC. The key here is “useful” work. For audio systems, the energy delivered in the audible bands is considered useful including the distortion products of the input signal. Sub-sonic (DC) and super-sonic components (>22kHz) are not useful. The difference between the power flowing from the power supply and the audio band power being transduced is dissipated in the LM48510 and in the transducer load. The amount of power dissipation in the LM48510 is very low. This is because the ON resistance of the switches used to form the output waveforms is typically less than 0.25 Ω. This leaves only the transducer load as a potential "sink" for the small excess of input power over audio band output power. The amplifier dissipates only a fraction of the excess power requiring no additional PCB area or copper plane to act as a heat sink. BOOST CONVERTER POWER DISSIPATION At higher duty cycles, the increased ON time of the FET means the maximum output current will be determined by power dissipation within the boost converter FET switch. The switch power dissipation from ON-state conduction is calculated by Equation 1. PDMAX(SWITCH) = DC x IIND(AVE) 2 x R DS(ON) (1) Where DC is the duty cycle. There will be some switching losses as well, so some derating needs to be applied when calculating IC power dissipation. SHUTDOWN FUNCTION To reduce power consumption while not in use, the amplifier of LM48510 contains shutdown circuitry that reduces current draw to less than 0.01µA. It is best to switch between ground and supply (PV1, V1) for minimum current usage while in the shutdown state. While the LM48510 may be disabled with shutdown voltages in between ground and supply, the idle current will be greater than the typical 0.01µA value. Increased THD may also be observed with voltages less than VDD on the SDAMP pin when in PLAY mode. The amplifier has an internal resistor connected between GND and SDAMP pins. The purpose of this resistor is to eliminate any unwanted state changes when the SDAMP pin is floating. The amplifier will enter the shutdown state when the SDAMP pin is left floating or if not floating, when the shutdown voltage has crossed the threshold. To minimize the supply current while in the shutdown state, the SDAMP pin should be driven to GND or left floating. If the SDAMP pin is not driven to GND, the amount of additional resistor current due to the internal shutdown resistor can be found by Equation (2) below. (VSD - GND) / 300kΩ (2) With only a 0.5V difference, an additional 1.7µA of current will be drawn while in the shutdown state. 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, and a pull-up resistor. One terminal of the switch is connected to GND. The other side is connected to the two shutdown pins and the terminal of the pull-up resistor. The remaining resistance terminal is connected to VDD. If the switch is open, then the external pull-up resistor connected to VDD will enable the LM48510. This scheme guarantees that the shutdown pins will not float thus preventing unwanted state changes. PROPER SELECTION OF EXTERNAL COMPONENTS Proper selection of external components in applications using integrated power amplifiers, and switching DC-DC converters, is critical for optimizing device and system performance. Consideration to component values must be used to maximize overall system quality. Copyright © 2006–2007, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM48510 |
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