LME49724 Datasheet, PDF (16/30 Pages) National Semiconductor (TI) – High Performance, High Fidelity, Fully-Differential Audio Operational Amplifier

LME49724
SNAS438A – NOVEMBER 2008 – REVISED APRIL 2013
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SINGLE SUPPLY OPERATION
The LME49724 can be operated from a single power supply, as shown in Figure 52. The supply voltage range is
limited to a minimum of 5V and a maximum of 36V. The common-mode output DC voltage will be set to the
midpoint of the supply voltage. The V_OCM pin can be used to adjust the common-mode output DC voltage on the
outputs, as described previously, if the supply voltage midpoint is not the desired DC voltage.
Figure 52. Single Supply Configuration
DRIVING A CAPACITIVE LOAD
The LME49724 is a high speed op amp with excellent phase margin and stability. Capacitive loads up to 100pF
will cause little change in the phase characteristics of the amplifiers and are therefore allowable.
Capacitive loads greater than 100pF must be isolated from the output. The most straightforward way to do this is
to put a resistor in series with the output. This resistor will also prevent excess power dissipation if the output is
accidentally shorted.
THERMAL PCB DESIGN
The LME49724's high operating supply voltage along with its high output current capability can result in
significant power dissipation. For this reason the LME49724 is provided in the exposed DAP SO PowerPad
package for improved thermal dissipation performance compared to other surface mount packages. The exposed
pad is designed to be soldered to a copper plane on the PCB which then acts as a heat sink. The thermal plane
can be on any layer by using multiple thermal vias under and outside the IC package. The vias under the IC
should have solder mask openings for the entire pad under the IC on the top layer but cover the vias on the
bottom layer. This method prevents solder from being pulled away from the thermal vias during the reflow
process resulting in optimum thermal conductivity.
Heat radiation from the PCB plane area is best accomplished when the thermal plane is on the top or bottom
copper layers. The LME49724 should always be soldered down to a copper pad on the PCB for both optimum
thermal performance as well as mechanical stability.
The exposed pad is for heat transfer and the thermal plane should either be electrically isolated or connected to
the same potential as the V_EE pin. For high frequency applications (f > 1MHz) or lower impedance loads, the pad
should be connected to a plane that is connected to the V_EE potential.
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