AUDIO

INPUT

COM

COMMON MODE SENSE

EQUIVALENT CIRCUIT

0

0.02

0.04

0.06

0.08

1

1.5

2

2.5

3

SUPPLY VOLTAGE (V)

-120

-100

-80

-60

-40

-20

0

10

100

1000

10000

100000

FREQUENCY (Hz)

LM48861, LM48861TMBD

SNAS450A – JUNE 2008 – REVISED MARCH 2010

www.ti.com

Typical Performance Characteristics (continued)

Shutdown Current

Crosstalk

vs

vs

Supply Voltage

Frequency

No Load

Application Information

GENERAL AMPLIFIER FUNCTION

The LM48861 headphone amplifier features National’s ground referenced architecture that eliminates the large

DC-blocking capacitors required at the outputs of traditional headphone amplifiers. A low-noise inverting charge

operate from these bipolar supplies, with the amplifier outputs biased about GND, instead of a nominal DC

signals, the large DC-blocking capacitors (typically 220

μF) are not necessary, conserving board space and

system cost, while improving frequency response.

COMMON MODE SENSE

The LM48861 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

LM48861 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 2). No additional external components are required. Connect COM

to GND if the common-mode sense feature is not in use.

MICRO POWER SHUTDOWN

The voltage applied to the shutdown (SHDN) pin controls the LM48861’s shutdown function. Activate micro-

power shutdown by applying a logic-low voltage to the SHDN pin. When active, the LM48861’s micro-power

shutdown feature turns off the amplifier’s bias circuitry, reducing the supply current. The trigger point is 0.4V

(max) for a logic-low level, and 1.4V (min) for a logic-high level. The low 0.1

μA (typ) shutdown current is

achieved by applying a voltage that is as near as ground as possible to the SHDN pin. A voltage that is higher

than ground may increase the shutdown current.

8

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