LME49724MR National Semiconductor, LME49724MR Datasheet - Page 15

• Manufacturer Part Number: LME49724MR
• Description: IC AMP AUDIO MONO AB HIFI 8PSOP
• Manufacturer: National Semiconductor

Specifications of LME49724MR

• Amplifier Type: Audio
• Number Of Circuits: 1
• Output Type: Differential
• Slew Rate: 18 V/µs
• Gain Bandwidth Product: 50MHz
• Current - Input Bias: 60nA
• Voltage - Input Offset: 200µV
• Current - Supply: 10mA
• Current - Output / Channel: 80mA
• Voltage - Supply, Single/dual (±): 5 V ~ 36 V, ±2.5 V ~ 18 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-PSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• -3db Bandwidth: -
• Other names: *LME49724MR

SINGLE SUPPLY OPERATION
The LME49724 can be operated from a single power supply,
as shown in Figure 4. 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
mode output DC voltage on the outputs, as described previ-
ously, if the supply voltage midpoint is not the desired DC
voltage.
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 pre-
vent 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 MSOP (PSOP) 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
FIGURE 4. Single Supply Configuration
OCM
pin can be used to adjust the common-
300442s1
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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
1MHz) or lower impedance loads, the pad should be con-
nected to a plane that is connected to the V
SUPPLY BYPASSING
The LME49724 should have its supply leads bypassed with
low-inductance capacitors such as leadless surface mount
(SMT) capacitors located as close as possible to the supply
pins. It is recommended that a 10μF tantalum or electrolytic
capacitor be placed in parallel with a 0.1μF ceramic or film
type capacitor on each supply pin. These capacitors should
be star routed with a dedicated ground return plane or large
trace for best THD performance. Placing capacitors too far
from the power supply pins, especially with thin connecting
traces, can lead to excessive inductance, resulting in degrad-
ed high-frequency bypassing. Poor high-frequency bypassing
can result in circuit instabilities. When using high bandwidth
power supplies, the value and number of supply bypass ca-
pacitors should be reduced for optimal power supply perfor-
mance.
BALANCE CABLE DRIVER
With high peak-to-peak differential output voltage and plenty
of low distortion drive current, the LME49724 makes an ex-
cellent balanced cable driver. Combining the single-to-differ-
ential configuration with a balanced cable driver results in a
high performance single-ended input to balanced line driver
solution.
Although the LME49724 can drive capacitive loads up to
100pF, cable loads exceeding 100pF can cause instability.
For such applications, series resistors are needed on the out-
puts before the capacitive load.
ANALOG-TO-DIGITAL CONVERTER (ADC)
APPLICATION
Figure 5 is a typical fully differential application circuit for driv-
ing an analog-to-digital converter (ADC). The additional com-
ponents of R
for stability and proper ADC sampling. ADC's commonly use
switched capacitor circuitry at the input. When the ADC sam-
ples the signal the current momentarily increases and may
disturb the signal integrity at the sample point causing a signal
glitch. Component C
pacitance of a typical ADC and acts as a charge reservoir
greatly reducing the effect of the signal sample by the ADC.
Resistors R
bility. The values shown are general values. Specific values
should be optimized for the particular ADC loading require-
ments.
The output reference voltage from the ADC can be used to
drive the V
the outputs of the LME49724. A buffer may be needed to drive
the LME49724's V
input impedance of the V
In order to minimize circuit distortion when using capacitors
in the signal path, the capacitors should be comprised of ei-
ther NPO ceramic, polystyrene, polypropylene or mica com-
position. Other types of capacitors may provide a reduced
distortion performance but for a cost improvement, so capac-
itor selection is dependent upon design requirements. The
performance/cost tradeoff for a specific application is left up
to the user.
OCM
5
and R
5
, R
pin to set the common-mode DC voltage on
6
EE
, and C
OCM
6
decouple the capacitive load, C
pin. For high frequency applications (f >
7
is significantly larger than the input ca-
pin if the ADC cannot drive the 50kΩ
OCM
7
are optional components and are
pin.
EE
potential.
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, for sta-