Datasheet

LM4810
www.ti.com SNAS125D –FEBRUARY 2001–REVISED APRIL 2013
APPLICATION INFORMATION
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the LM4810's shutdown function. Activate micro-power
shutdown by applying a logic high voltage to the SHUTDOWN pin. The logic threshold is typically V
DD
/2. When
active, the LM4810's micro-power shutdown feature turns off the amplifier's bias circuitry, reducing the supply
current. The low 0.4µA typical shutdown current is achieved by applying a voltage that is as near as V
DD
as
possible to the SHUTDOWN pin. A voltage that is less than V
DD
may increase the shutdown current.
There are a few ways to control the micro-power shutdown. These include using a single-pole, single-throw
switch, a microprocessor, or a microcontroller. When using a switch, connect an external 100kΩ pull-up resistor
between the SHUTDOWN pin and V
DD
. Connect the switch between the SHUTDOWN pin and GND. Select
normal amplifier operation by closing the switch. Opening the switch connects the SHUTDOWN pin to V
DD
through the pull-up resistor, activating micro-power shutdown. The switch and resistor ensure that the
SHUTDOWN pin will not float. This prevents unwanted state changes. In a system with a microprocessor or a
microcontroller, use a digital output to apply the control voltage to the SHUTDOWN pin. Driving the SHUTDOWN
pin with active circuitry eliminates the pull-up resistor.
EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATION
The LM4810's exposed-Dap (die attach paddle) package (NGL0008B) provides a low thermal resistance
between the die and the PCB to which the part is mounted and soldered. This allows rapid heat transfer from the
die to the surrounding PCB copper traces, ground plane, and surrounding air.
The NGL0008B package should have its DAP soldered to a copper pad on the PCB. The DAP's PCB copper pad
may be connected to a large plane of continuous unbroken copper. This plane forms a thermal mass, heat sink,
and radiation area.
However, since the LM4810 is designed for headphone applications, connecting a copper plane to the DAP's
PCB copper pad is not required. Figure 33 in Typical Performance Characteristics shows that the maximum
power dissipated is just 45mW per amplifier with a 5V power supply and a 32Ω load.
Further detailed and specific information concerning PCB layout, fabrication, and mounting an NGL0008B
(WSON) package is available from Texas Instruments' Package Engineering Group under application note
AN1187.
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.
P
DMAX
= (V
DD
)
2
/ (2π
2
R
L
) (1)
Since the LM4810 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
LM4810 does not require heat sinking over a large range of ambient temperature. From Equation 1, assuming a
5V power supply and a 32Ω load, the maximum power dissipation point is 40mW per amplifier. Thus the
maximum package dissipation point is 80mW. The maximum power dissipation point obtained must not be
greater than the power dissipation that results from Equation 2:
P
DMAX
= (T
JMAX
− T
A
) / θ
JA
(2)
For package DGK0008A, θ
JA
= 210°C/W. T
JMAX
= 150°C for the LM4810. Depending on the ambient
temperature, T
A
, 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 decreased, the load impedance increased or T
A
reduced. For the typical
application of a 5V power supply, with a 32Ω load, the maximum ambient temperature possible without violating
the maximum junction temperature is approximately 133.2°C provided that device operation is around the
maximum power dissipation point. Power dissipation 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 accordingly. Refer
to Typical Performance Characteristics for power dissipation information for lower output powers.
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