Datasheet

LM4809, LM4809LQBD
www.ti.com SNAS126F –FEBRUARY 2001–REVISED APRIL 2013
APPLICATION INFORMATION
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the LM4809's shutdown function. Activate micro-power
shutdown by applying a logic low voltage to the SHUTDOWN pin. The logic threshold is typically V
DD
/2. When
active, the LM4809'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 GND as
possible to the SHUTDOWN pin. A voltage that is above GND 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-down
resistor between the SHUTDOWN pin and GND. Connect the switch between the SHUTDOWN pin and V
DD
.
Select normal amplifier operation by closing the switch. Opening the switch connects the SHUTDOWN pin to
GND through the pull-down 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-down resistor.
EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATION
The LM4809's exposed-Dap (die attach paddle) package (LD or LQ) 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 LD or LQ 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 LM4809 is designed for headphone applications, connecting a copper plane to the DAP's
PCB copper pad is not required. Figure 34 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 or
NGP0008A 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 LM4809 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
LM4809 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)
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