Datasheet

LME49600

OUT

10 PF

V-

V+

0.1PF

LME49600

www.ti.com

SNAS422E –JANUARY 2008–REVISED APRIL 2013

AUDIO BUFFERS

Audio buffers or unity-gain followers, have large current gain and a voltage gain of one. Audio buffers serve

many applications that require high input impedance, low output impedance and high output current. They also

offer constant gain over a very wide bandwidth.

Buffers serve several useful functions, either in stand-alone applications or in tandem with operational amplifiers.

In stand-alone applications, their high input impedance and low output impedance isolates a high impedance

source from a low impedance load.

SUPPLY BYPASSING

The LME49600 will place great demands on the power supply voltage source when operating in applications that

require fast slewing and driving heavy loads. These conditions can create high amplitude transient currents. A

power supply’s limited bandwidth can reduce the supply’s ability to supply the needed current demands during

these high slew rate conditions. This inability to supply the current demand is further exacerbated by PCB trace

or interconnecting wire inductance. The transient current flowing through the inductance can produce voltage

transients.

For example, the LME49600’s output voltage can slew at a typical ±2000V/μs. When driving a 100Ω load, the

di/dt current demand is 20 A/μs. This current flowing through an inductance of 50nH (approximately 1.5” of 22

gage wire) will produce a 1V transient. In these and similar situations, place the parallel combination of a solid

5μF to 10μF tantalum capacitor and a ceramic 0.1μF capacitor as close as possible to the device supply pins.

Ceramic capacitors with values in the range of 10μF to 100μF, ceramic capacitor have very lower ESR (typically

less than 10mΩ) and low ESL when compared to the same valued tantalum capacitor. The ceramic capacitors,

therefore, have superior AC performance for bypassing high frequency noise.

In less demanding applications that have lighter loads or lower slew rates, the supply bypassing is not as critical.

Capacitor values in the range of 0.01μF to 0.1μF are adequate.

SIMPLIFIED LME49600 CIRCUIT DIAGRAM

The LME49600’s simplified circuit diagram is shown in Figure 2. The diagram shows the LME49600’s

complementary emitter follower design, bias circuit and bandwidth adjustment node.

Figure 29 shows the LME49600 connected as an open-loop buffer. The source impedance and optional input

resistor, R

, can alter the frequency response. As previously stated, the power supplies should be bypassed with

capacitors connected close to the LME49600’s power supply pins. Capacitor values as low as 0.01μF to 0.1μF

will ensure stable operation in lightly loaded applications, but high output current and fast output slewing can

demand large current transients from the power supplies. Place a recommended parallel combination of a solid

tantalum capacitor in the 5μF to 10μF range and a ceramic 0.1μF capacitor as close as possible to the device

supply pins.

Figure 29. Buffer Connections

Product Folder Links: LME49600