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TPA2000D1 Datasheet(PDF) 11 Page - Texas Instruments |
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TPA2000D1 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 22 page When to Use An Output Filter C2 C1 L1 L2 OUT− OUT+ Gain Setting Via GAIN0 and GAIN1 Inputs TPA2000D1-Q1 www.ti.com ........................................................................................................................................ SGLS137E – SEPTEMBER 2002 – REVISED OCTOBER 2008 damage could occur to the speaker if the voice coil is not designed to handle the additional power. To size the speaker for added power, the ripple current dissipated in the load needs to be calculated by subtracting the theoretical supplied power (PSUP THEORETICAL) from the actual supply power (PSUP) at maximum output power (POUT). The switching power dissipated in the speaker is the inverse of the measured efficiency (ηMEASURED) minus the theoretical efficiency ( η THEORETICAL) all multiplied by POUT. PSPKR = PSUP – PSUP THEORETICAL (at max output power) (1) PSPKR = POUT(PSUP/POUT – PSUP THEORETICAL/POUT) (at max output power) (2) PSPKR = POUT(1/ηTHEORETICAL – 1/ηTHEORETICAL) (at max output power) (3) The maximum efficiency of the TPA2000D1 with an 8- Ω load is 85%. Using Equation 3 with the efficiency at maximum power (78%), we see that there is an additional 106 mW dissipated in the speaker. The added power dissipated in the speaker is not an issue as long as it is taken into account when choosing the speaker. Design the TPA2000D1 without the filter if the traces from amplifier to speaker are short. The TPA2000D1 passed FCC and CE radiated emissions with no shielding with speaker wires eight inches long or less. Notebook PCs and powered speakers where the speaker is in the same enclosure as the amplifier are good applications for class-D without a filter. A ferrite bead filter (shown in Figure 11) often can be used if the design is failing radiated emissions without a filter, and the frequency sensitive circuit is greater than 1 MHz. This is good for circuits that have to pass only FCC and CE because FCC and CE test only radiated emissions greater than 30 MHz. If choosing a ferrite bead, choose one with high impedance at high frequencies, but low impedance at low frequencies. Use an output filter if the EMI sensitive circuits are low frequency (<1 MHz) and/or the leads from amplifier to speaker are long. The LC output filter is shown in Figure 11. • L1 = L2 = 22 µH (DCR = 110 mΩ, part number = SCD0703T-220 M-S, manufacturer = GCI) • C1 = C2 = 1 µF The ferrite filter is shown in Figure 11, where L is a ferrite bead. • L1 = L2 = ferrite bead (part number = MPZ1608S221, manufacturer = TDKI) • C1 = C2 = 1 nF Figure 11. Class-D Output Filter The gain of the TPA2000D1 is set by two input terminals, GAIN0 and GAIN1. The gains listed in Table 2 are realized by changing the taps on the input resistors inside the amplifier. This causes the input impedance (Zi) to be dependent on the gain setting. The actual gain settings are controlled by ratios of resistors, so the actual gain distribution from part-to-part is quite good. However, the input impedance may shift by 30% due to shifts in the actual resistance of the input resistors. For design purposes, the input network (discussed in the next section) should be designed assuming an input impedance of 20 k Ω, which is the absolute minimum input impedance of the TPA2000D1. At the higher gain settings, the input impedance could increase as high as 115 k Ω. Copyright © 2002–2008, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Link(s): TPA2000D1-Q1 |
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