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LM4995 Datasheet(PDF) 11 Page - Texas Instruments |
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LM4995 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 23 page SHUTDOWN VOLTAGE (V) 0 100 10 20 30 40 50 60 70 80 90 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 VOLTAGE SUPPLY (V) 2.0 3.0 4.0 5.0 6.0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 THD+N = 10% THD+N = 1% LM4995, LM4995TMBD www.ti.com SNAS329F – APRIL 2006 – REVISED NOVEMBER 2009 Typical Performance Characteristics (continued) Output Power vs Shutdown Voltage VSDIL Supply Voltage VDD = 5V RL = 8Ω Application Information BRIDGE CONFIGURATION EXPLANATION As shown in Figure 1, the LM4995 has two internal operational amplifiers. The first amplifier's gain is externally configurable, while the second amplifier is internally fixed in a unity-gain, inverting configuration. The closed-loop gain of the first amplifier is set by selecting the ratio of Rf to Ri while the second amplifier's gain is fixed by the two internal 20k Ω resistors. Figure 1 shows that the output of amplifier one serves as the input to amplifier two which results in both amplifiers producing signals identical in magnitude, but out of phase by 180°. Consequently, the differential gain for the IC is AVD= 2 *(Rf/Ri) (1) By driving the load differentially through outputs Vo1 and Vo2, an amplifier configuration commonly referred to as “bridged mode” is established. Bridged mode operation is different from the classical single-ended amplifier configuration where one side of the load is connected to ground. A bridge amplifier design has a few distinct advantages over the single-ended configuration, as it provides differential drive to the load, thus doubling output swing for a specified supply voltage. Four times the output power is possible as compared to a single-ended amplifier under the same conditions. This increase in attainable output power assumes that the amplifier is not current limited or clipped. In order to choose an amplifier's closed- loop gain without causing excessive clipping, please refer to the Audio Power Amplifier Design section. A bridge configuration, such as the one used in LM4995, also creates a second advantage over single-ended amplifiers. Since the differential outputs, Vo1 and Vo2, are biased at half-supply, no net DC voltage exists across the load. This eliminates the need for an output coupling capacitor which is required in a single supply, single- ended amplifier configuration. Without an output coupling capacitor, the half-supply bias across the load would result in both increased internal IC power dissipation and also possible loudspeaker damage. POWER DISSIPATION Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or single-ended. A direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in internal power dissipation. Since the LM4995 has two operational amplifiers in one package, the maximum internal power dissipation is 4 times that of a single-ended amplifier. The maximum power dissipation for a given application can be derived from the power dissipation graphs or from Equation 1. PDMAX = 4*(VDD) 2/(2π2R L) (2) Copyright © 2006–2009, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM4995 LM4995TMBD |
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