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LM48822TLEVAL Datasheet(PDF) 11 Page - Texas Instruments |
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LM48822TLEVAL Datasheet(HTML) 11 Page - Texas Instruments |
11 / 22 page CHARGE PUMP C1P C1N CPVSS C1 C2 VDD VSS HI-Z INCOMING AUDIO SIGNAL OUT_ LM48822, LM48822TLEVAL www.ti.com SNAS456C – MAY 2008 – REVISED MAY 2013 GENERAL AMPLIFIER EXPLANATION The LM48822 features a differential input stage, which offers improved noise rejection compared to a single- ended input amplifier. Because a differential input amplifier amplifies the difference between the two input signals, any component common to both signals is cancelled. An additional benefit of the differential input structure is the possible elimination of the DC input blocking capacitors. Since the DC component is common to both inputs, and thus cancelled by the amplifier, the LM48822 can be used without input coupling capacitors when configured with a differential input signal. CHARGE PUMP ONLY MODE In applications where the headphone jack is used as both an output and input port, signals such as a microphone input can appear on the headphone amplifier output. Traditional charge pump headphone amplifiers can clamp or distort the signals that appear on their output. Without the charge pump active, generating the negative voltage supply, the internal protection diodes of the amplifier clamp the incoming signal, distorting the negative half cycle, see Figure 24. The LM48822 charge pump only mode eliminates this problem. In charge pump only mode, the amplifiers are disabled, while the charge pump remains active. The disabled amplifier outputs present a high impedance (1M Ω) load to the incoming signal. The charge pump maintains the negative rail, allowing the incoming signal to swing between VDD and VSS without any interference from the device. Set bit B4 (CP_ONLY) of the MODE CONTROL register to 1 for charge pump only mode. Setting CP_ONLY = 1 disables both the left and right channels, regardless of the status of the shutdown control bits. Set CP_ONLY = 0 for normal operation. Figure 24. Back-Driving the LM48822 Outputs COMMON MODE SENSE The LM48822 features a ground (common mode) sensing feature. In noisy applications, or where the headphone jack is used as a line out to other devices, noise pick up and ground imbalance can degrade audio quality. The LM48822 COM input senses and corrects any noise at the headphone return, or any ground imbalance between the headphone return and device ground, improving audio reproduction. Connect COM directly to the headphone return terminal of the headphone jack Figure 25. No additional external components are required. Connect COM to GND if the common-mode sense feature is not in use. Copyright © 2008–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM48822 LM48822TLEVAL |
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