Datasheet

BW
+
U4
5
3
2
1
4
+
+
LME49600
C9
4.7 PF
C22
0.1 PF
V-
C10
4.7 PF
C21
0.1 PF
V+
+
U2-A
8
4
3
2
1
LME49720NA
C4
1.0 PF
V-
C3
1.0 PF
V+
-
R2
1k
-
U2-B
6
5
7
LME49720NA
C8
1.0 PF
C7
1.0 PF
+
R11
1M
R12
1M
VR1-B
10k
R6
1k
JU4
R4
1k
BW
+
U3
5
3
2
1
4
+
+
LME49600
C23
4.7 PF
C20
0.1 PF
V-
C24
4.7 PF
C19
0.1 PF
V+
+
U1-A
8
4
3
2
1
LME49720NA
C2
1.0 PF
V-
C1
1.0 PF
V+
-
R1
1k
-
U1-B
6
5
7
LME49720NA
C6
1.0 PF
C5
1.0 PF
+
R9
1M
R10
1M
VR1-A
10k
R5
1k
JU8
R3
1k
JU17
JU1
JU15
JU14
1
2
4
5
3
HP32
1
2
4
5
3
HP31
2
1J2
2
1J1
LME49600
SNAS422E –JANUARY 2008–REVISED APRIL 2013 www.ti.com
APPLICATION INFORMATION
HIGH PERFORMANCE, HIGH FIDELITY HEADPHONE AMPLIFIER
The LME49600 is the ideal solution for high output, high performance high fidelity head phone amplifiers. When
placed in the feedback loop of the LME49710, LME49720 or LME49740 High Performance, High Fidelity audio
operational amplifier, the LME49600 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 AC signal gain is set by resistors R2, R4, and R6.
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.
Figure 28. LME49600 Delivers High Output Current for this High Performance Headphone Amplifier
10 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LME49600