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LM48310 bảng dữ liệu(PDF) 10 Page - Texas Instruments |
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10 / 23 page LM48310 SNAS430C – NOVEMBER 2007 – REVISED JUNE 2009 www.ti.com APPLICATION INFORMATION GENERAL AMPLIFIER FUNCTION The LM48310 mono Class D audio power amplifier features a filterless modulation scheme that reduces external component count, conserving board space and reducing system cost. With no signal applied, the outputs (VOUTA and VOUTB) switch between VDD and GND 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. With the input signal applied, the duty cycle (pulse width) of the LM48310 outputs changes. For increasing output voltage, the duty cycle of VOUTAincreases, while the duty cycle of VOUTB decreases. For decreasing output voltages, the converse occurs. The difference between the two pulse widths yields the differential output voltage. ENHANCED EMISSIONS SUPPRESSION SYSTEM (E 2S) The LM48310 features ’s patent-pending E2S system that reduces EMI, while maintaining high quality audio reproduction and efficiency. The E2S system features a synchronizable oscillator with selectable spread spectrum, and advanced edge rate control (ERC). The LM48310 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. The overall result of the E2S system is a filterless Class D amplifier that passes FCC Class B radiated emissions standards with 20in of twisted pair cable, with excellent 0.03% THD+N and high 88% efficiency. FIXED FREQUENCY MODE (SYNC_IN = GND) The LM48310 features two modulations schemes, a fixed frequency mode and a spread spectrum mode. Select the fixed frequency mode by setting SYNC_IN = GND. In fixed frequency mode, the amplifier output switch at a constant 300kHz. In fixed frequency mode, the output spectrum consists of the fundamental and its associated harmonics (see Typical Performance Characteristics). SPREAD SPECTRUM MODE (SYNC_IN = VDD) The logic selectable spread spectrum mode eliminates the need for output filters, ferrite beads or chokes. In spread spectrum mode, the switching frequency varies randomly by 30% about a 300kHz center frequency, reducing the wideband spectral contend, improving EMI emissions radiated by the speaker and associated cables and traces. Where a fixed frequency class D exhibits large amounts of spectral energy at multiples of the switching frequency, the spread spectrum architecture of the LM48310 spreads that energy over a larger bandwidth (See Typical Performance Characteristics). The cycle-to-cycle variation of the switching period does not affect the audio reproduction, efficiency, or PSRR. Set SYNC_IN = VDD for spread spectrum mode. EXTERNAL CLOCK MODE (SYNC_IN = CLOCK) Connecting a clock signal to SYNC_IN synchronizes the LM48310 oscillator to an external clock, moving the output spectral components out of a sensitive frequency band, and minimizing audible beat frequencies when multiple LM48310s are used in a single system. The LM48310 accepts an external clock frequency between 200kHz and 1MHz. The LM48310 can be synchronized to a spread spectrum clock, allowing multiple LM48310s to be synchronized in spread spectrum mode (see Typical Performance Characteristics). SYNC_OUT SYNC_OUT is a clock output for synchronizing external devices. The SYNC_OUT signal is identical in frequency and duty cycle of the amplifier’s switching frequency. When the LM48310 is in fixed frequency mode, SYNC_OUT is a fixed, 300kHz clock. When the LM48310 is in spread spectrum mode, SYNC_OUT is an identical spread spectrum clock. When the LM48310 is driven by an external clock, SYNC_OUT is identical to the external clock. If unused, leave SYNC_OUT floating. Multiple LM48310s can be synchronized to a single clock. In Figure 27, device U1 is the master, providing a spread spectrum clock to the slave device (U2). This configuration synchronizes the switching frequencies of the two devices, eliminating any audible beat frequencies. Because SYNC_OUT has no audio content, there is minimal THD+N degredation or crosstalk between the devices, Figure 28 - Figure 30. 10 Submit Documentation Feedback Copyright © 2007–2009, Texas Instruments Incorporated Product Folder Links: LM48310 |
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