LM4858LDX National Semiconductor, LM4858LDX Datasheet - Page 12

• Manufacturer Part Number: LM4858LDX
• Manufacturer: National Semiconductor

Specifications of LM4858LDX

• Operational Class: Class-AB
• Audio Amplifier Function: Headphone/Speaker
• Total Harmonic Distortion: 1@32Ohm@95mW%
• Single Supply Voltage (typ): 3/5V
• Dual Supply Voltage (typ): Not RequiredV
• Supply Current (max): 7@5VmA
• Power Supply Requirement: Single
• Rail/rail I/o Type: No
• Single Supply Voltage (min): 2.4V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 14
• Package Type: LLP
• Lead Free Status / Rohs Status: Not Compliant

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Application Information
amplifier’s closed-loop gain without causing excessive out-
put signal clipping, please refer to the Audio Power Ampli-
fier Design section.
A bridge configuration, such as the one used in LM4858,
also creates a second advantage over single-ended amplifi-
ers. Since the differential outputs, BTL OUT- and BTL OUT+,
are biased at half-supply, no net DC voltage exists across
the load. This eliminates the need for the output coupling
capacitor that a single supply, single-ended amplifier con-
figuration requires. Eliminating an output coupling capacitor
in a single-ended configuration forces the half-supply bias
voltage across the load. This increases internal IC power
dissipation and may cause permanent loudspeaker damage.
POWER DISSIPATION
Whether the power amplifier is bridged or single-ended,
power dissipation is a major concern when designing the
amplifier. Equation 2 states the maximum power dissipation
point for a single-ended amplifier operating at a given supply
voltage and driving a specified load.
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is an increase in
internal power dissipation. Equation 3 states the maximum
power dissipation point for a bridge amplifier operating at the
same given conditions.
The LM4858 is designed to drive either two single-ended
loads simultaneously or one mono bridged-tied load. In SE
mode, the maximum internal power dissipation is 2 times
that of Equation 2. In BTL mode, the maximum internal
power dissipation is the result of Equation 3. Even with this
substantial increase in power dissipation, the LM4858 does
not require heatsinking. The power dissipation from Equation
3 must not be greater than the power dissipation predicted
by Equation 4:
For the package MUB10A, θ
for the LM4858. Depending on the ambient temperature, T
of the surroundings, Equation 4 can be used to find the
maximum internal power dissipation supported by the IC
packaging. If the result of Equation 3 is greater than that of
Equation 4, then either the supply voltage must be de-
creased, the load impedance increased, or the ambient tem-
perature reduced. For the typical application of a 5V power
supply, and an 8Ω bridged load, the maximum ambient
temperature possible without violating the maximum junction
temperature is approximately 27˚C for package MUB10A.
This assumes the device operates at maximum power dis-
sipation and uses surface mount packaging. Internal power
dissipation is a function of output power. If typical operation
is not around the maximum power dissipation point, opera-
tion at higher ambient temperatures is possible. Refer to the
Typical Performance Characteristics curves for power dis-
sipation information for different output power levels.
P
P
DMAX
DMAX
= 4 x (V
P
= (V
DMAX
DD
DD
)
= (T
2
)
/ (2π
2
JMAX
/ (2π
JA
2
R
= 194˚C/W. T
2
- T
L
R
): Single-Ended
L
A
): Bridge Mode
) / θ
JA
(Continued)
JMAX
= 150˚C
(2)
(3)
(4)
A
,
12
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. The capacitor location on both the bypass and
power supply pins should be as close to the device as
possible. The value of the pin bypass capacitor, C
affects the LM4858’s half-supply voltage stability and PSRR.
The stability and supply rejection increase as the bypass
capacitor’s value increases Typical applications employ a 5V
regulator with a 10µF and a 0.1µF bypass capacitors which
aid in supply filtering. This does not eliminate the need for
bypassing the supply nodes of the LM4858. The selection of
bypass capacitors, especially C
desired PSRR requirements, click and pop performance,
system cost, and size constraints.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the
LM4858 features amplifier bias circuitry shutdown. This shut-
down function is activated by applying a logic high to the
SHUTDOWN pin. The trigger point is 2.0V minimum for a
logic high level, and 0.8V maximum for a logic low level. It is
best to switch between ground and the supply, V
ensure correct shutdown operation. By switching the SHUT-
DOWN pin to V
minimized in idle mode. Whereas the device will be disabled
with shutdown voltages less than V
be greater than the typical value of 18µA. In either case, the
SHUTDOWN pin should be tied to a fixed voltage to avoid
unwanted state changes.
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry. This provides
a quick, smooth shutdown transition. Another solution is to
use a single-pole, single-throw switch in conjunction with an
external pull-up resistor. When the switch is closed, the
SHUTDOWN pin is connected to ground and enables the
amplifier. If the switch is open, the external pull-up resistor,
R
the SHUTDOWN pin will not float, thus preventing unwanted
state changes.
HP-IN FUNCTION
The LM4858 features a headphone control pin, HP-IN, that
enables the switching between BTL and SE modes. A logic-
low to HP-IN activates the BTL mode, while a logic-high
activates the SE mode. The trigger point is 2.0V minimum for
a logic high level and 0.8V maximum for a logic low level. A
microcontroller or microprocessor output should be used to
control the headphone sense circuitry. This provides a quick,
smooth shutdown transition. Another solution is to use a
single-pole, single-throw switch in conjunction with an exter-
nal pull-up resistor. When the switch is closed, the HP-IN pin
is connected to the ground and activates BTL mode. If the
switch is open, the external pull-up resistor, R
vate SE mode. This scheme guarantees that the HP-IN pin
will not float, thus preventing unwanted state changes.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications us-
ing integrated power amplifiers is critical for optimum device
and system performance. While the LM4858 is tolerant to a
variety of external component combinations, consideration
must be given to the external component values that maxi-
mize overall system quality.
PU2
will disable the LM4858. This scheme guarantees that
DD
, the LM4858 supply current draw will be
B
, is thus dependent upon
DD
, the idle current may
PU1
B
, will acti-
, directly
DD
, to