LME49610 Datasheet, PDF (9/21 Pages) National Semiconductor (TI) – High Performance, High Fidelity, High Current Audio Buffer

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LME49610
SNAS435B – APRIL 2008 – REVISED APRIL 2013
TYPICAL APPLICATION DIAGRAM
R_FB
V⁺
0.1 PF
R_IN
10 PF
+
-
V_CC
1
2
LME49860
V_CC
IN _LME49610
OUT
+
V_EE 0.1 PF
V_EE 10 PF
R_L
+
BW
V^-
Figure 27. High Performance, High Fidelity LME49610 Audio Buffer Application
APPLICATION INFORMATION
HIGH PERFORMANCE, HIGH FIDELITY HEADPHONE AMPLIFIER
The LME49610 is the ideal solution for high output, high performance high fidelity headphone amplifiers. When
placed in the feedback loop of the LME49710, LME49720 or LME49740 High Performance, High Fidelity audio
operational amplifier, the LME49610 is able to drive 32Ω headphones to a dissipation of greater than 500mW at
0.00003% THD+N while operating on ±15V power supply voltages. The circuit schematic for a typical headphone
amplifier is shown in Figure 28.
Operation
The following describes the circuit operation for the headphone amplifier’s Left Channel. The Right Channel
operates identically.
The audio input signal is applied to the input jack (HP31 or J1/J2) and dc-coupled to the volume control, VR1.
The output signal from VR1’s wiper is applied to the non-inverting input of U2-A, an LME49720 High
Performance, High Fidelity audio operational amplifier. U2-A’s signal gain is set by resistors R2 and R4. To allow
for a DC-coupled signal path and to ensure minimal output DC voltage regardless of the closed-loop gain, the
other half of the U2 is configured as a DC servo. By constantly monitoring U2-A’s output, the servo creates a
voltage that compensates for any DC voltage that may be present at the output. A correction voltage is
generated and applied to the feedback node at U2-A, pin 2. The servo ensures that the gain at DC is unity.
Based on the values shown in Figure 28, the RC combination formed by R11 and C7 sets the servo’s high-pass
cutoff at 0.16Hz. This is over two decades below 20Hz, minimizing both amplitude and phase perturbations in the
audio frequency band’s lowest frequencies.
Copyright © 2008–2013, Texas Instruments Incorporated
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