LM4880N National Semiconductor, LM4880N Datasheet - Page 10

• Manufacturer Part Number: LM4880N
• Description: IC AMP AUDIO PWR .325W STER 8DIP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4880N

• Output Type: 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 325mW x 2 @ 8 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Features: Shutdown, Thermal Protection
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *LM4880N

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Typical Performance Characteristics
Application Information
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the
LM4880 contains a shutdown pin to externally turn off the
amplifier’s bias circuitry. This shutdown feature turns the
amplifier off when a logic high is placed on the shutdown pin.
The trigger point between a logic low and logic high level is
typically half supply. It is best to switch between ground and
the supply to provide maximum device performance. By
switching the shutdown pin to V
rent draw will be minimized in idle mode. While the device
will be disabled with shutdown pin voltages less than V
the idle current may be greater than the typical value of 0.7
µA. In either case, the shutdown pin should be tied to a
definite voltage because leaving the pin floating may result in
an unwanted shutdown condition.
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry which pro-
vides a quick, smooth transition into shutdown. Another so-
lution is to use a single-pole, single-throw switch in conjunc-
tion with an external pull-up resistor. When the switch is
closed, the shutdown pin is connected to ground and en-
ables the amplifier. If the switch is open, then the external
pull-up resistor will disable the LM4880. This scheme guar-
antees that the shutdown pin will not float which will prevent
unwanted state changes.
POWER DISSIPATION
Power dissipation is a major concern when using any power
amplifier and must be thoroughly understood to ensure a
successful design. Equation (1) states the maximum power
dissipation point for a single-ended amplifier operating at a
given supply voltage and driving a specified output load.
Since the LM4880 has two operational amplifiers in one
package, the maximum internal power dissipation point is
twice that of the number which results from Equation (1).
Even with the large internal power dissipation, the LM4880
does not require heat sinking over a large range of ambient
temperatures. From Equation (1), assuming a 5V power
supply and an 8Ω load, the maximum power dissipation
point is 158 mW per amplifier. Thus the maximum package
P
Frequency Response
DMAX
Typical Application
= (V
DD
DD
)
2
/(2π
, the LM4880 supply cur-
2
R
L
)
01234333
DD
(1)
,
10
(Continued)
dissipation point is 317 mW. The maximum power dissipa-
tion point obtained must not be greater than the power
dissipation that results from Equation (2):
For the LM4880 surface mount package, θ
T
of the system surroundings, Equation (2) can be used to find
the maximum internal power dissipation supported by the IC
packaging. If the result of Equation (1) is greater than that of
Equation (2), 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, with an 8Ω load, the maximum ambient temperature
possible without violating the maximum junction temperature
is approximately 96˚C provided that device operation is
around the maximum power dissipation point. Power dissi-
pation is a function of output power and thus, if typical
operation is not around the maximum power dissipation
point, the ambient temperature may be increased accord-
ingly. Refer to the Typical Performance Characteristics
curves for power dissipation information for lower output
powers.
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. As displayed in the Typical Performance Charac-
teristics section, the effect of a larger half supply bypass
capacitor is improved low frequency PSRR due to increased
half-supply stability. Typical applications employ a 5V regu-
lator with 10 µF and a 0.1 µF bypass capacitors which aid in
supply stability, but do not eliminate the need for bypassing
the supply nodes of the LM4880. The selection of bypass
capacitors, especially C
low frequency PSRR, click and pop performance as ex-
plained in the section, Proper Selection of External Com-
ponents section, system cost, and size constraints.
AUTOMATIC SHUTDOWN CIRCUIT
As shown in Figure 2, the LM4880 can be set up to auto-
matically shutdown when a load is not connected. This cir-
cuit is based upon a single control pin common in many
headphone jacks. This control pin forms a normally closed
JMAX
= 150˚C. Depending on the ambient temperature, T
Power Derating Curve
P
DMAX
B
= (T
, is thus dependant upon desired
JMAX
-T
A
)/θ
JA
JA
01234334
= 170˚ C/W and
(2)
A
,