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LM48413 bảng dữ liệu(PDF) 9 Page - Texas Instruments |
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LM48413 bảng dữ liệu(HTML) 9 Page - Texas Instruments |
9 / 23 page LM48413 www.ti.com SNAS460A – NOVEMBER 2008 – REVISED JANUARY 2009 APPLICATION INFORMATION GENERAL AMPLIFIER FUNCTION The LM48413 stereo Class D audio power amplifier features a filterless modulation scheme that reduces external component count, conserving board space and reducing system cost. The outputs of the device transition from PVDD to GND with a 390kHz switching frequency. With no signal applied, the outputs switch with a 50% duty cycle, in phase, causing the two outputs to cancel. This cancellation results in no net voltage across the speaker, thus there is no current to the load in the idle state. When an input signal is applied, the duty cycle (pulse width) of the LM48413 output's change. For increasing output voltage, the duty cycle of one side of each output increases, while the duty cycle of the other side of each output decreases. For decreasing output voltages, the converse occurs. The difference between the two pulse widths yields the differential output voltage. SHUTDOWN FUNCTION The LM48413 features a low current shutdown mode. Set SD = GND to disable the amplifier and reduce supply current to 0.03 μA. Switch SD between GND and VDD for minimum current consumption in shutdown. The LM48413 may be disabled with shutdown voltages in between GND and VDD, but the idle current will be greater than the typical value. The LM48413 shutdown input has an internal 300k Ω pull-down resistor. The purpose of this resistor is to eliminate any unwanted state changes when this pin is floating. To minimize shutdown current, it should be driven to GND or left floating. If it is not driven to GND, or floating, a small increase in shutdown supply current will be noticed. SPREAD SPECTRUM The LM48413 outputs are modulated in spread spectrum scheme eliminating the need for output filters, ferrite beads or chokes. During its operation, the switching frequency varies randomly by 30% about a 390kHz center frequency, reducing the wideband spectral content and improving EMI emissions radiated by the speaker and associated cables and traces. A fixed frequency class D exhibits large amounts of spectral energy at multiples of the switching frequency. The spread spectrum architecture of the LM48413 spreads the same energy over a larger bandwidth. The cycle-to-cycle variation of the switching period does not affect the audio reproduction, efficiency, or PSRR. ENHANCED EMISSIONS SUPPRESSION SYSTEM (E 2S) The LM48413 features Texas Instruments’ patented E2S system that further reduces EMI, while maintaining high quality audio reproduction and efficiency. The advanced edge rate control (ERC) embedded within the E2S system works simultaneously with the spread spectrum already activated. The LM48413 ERC greatly reduces the high frequency components of the output square waves by controlling the output rise and fall times, slowing the transitions to reduce RF emissions, while maximizing THD+N and efficiency performance. DIFFERENTIAL AMPLIFIER EXPLANATION As logic supplies continue to shrink, system designers are increasingly turning to differential analog signal handling to preserve signal to noise ratios with restricted voltage swings. The LM48413 features two fully differential speaker amplifiers. A differential amplifier amplifies the difference between the two input signals. Traditional audio power amplifiers have typically offered only single-ended inputs resulting in a 6dB reduction of SNR relative to differential inputs. The LM48413 also offers the possibility of DC input coupling which eliminates the input coupling capacitors. A major benefit of the fully differential amplifier is the improved common mode rejection ratio (CMRR) over single-ended input amplifiers. The increased CMRR of the differential amplifier reduces sensitivity to ground offset related noise injection, especially important in noisy systems. POWER DISSIPATION AND EFFICIENCY The major benefit of a Class D amplifier is increased efficiency versus a Class AB. The efficiency of the LM48413 is attributed to the region of operation of the transistors in the output stage. The Class D output stage acts as current steering switches, consuming negligible amounts of power compared to a Class AB amplifier. Most of the power loss associated with the output stage is due to the IR loss of the MOSFET on-resistance, along with switching losses due to gate charge. Copyright © 2008–2009, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM48413 |
Số phần tương tự - LM48413_14 |
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Mô tả tương tự - LM48413_14 |
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