Texas Instruments 6W Stereo Audio Power Amplifier LM4940TSBD/NOPB LM4940TSBD/NOPB 데이터 시트
제품 코드
LM4940TSBD/NOPB
SNAS219C – OCTOBER 2003 – REVISED MAY 2013
T
A
= T
JMAX
- P
DMAX-SE
θ
JA
(3)
For a typical application with a 12V power supply and two 4
Ω
SE loads, the maximum ambient temperature that
allows maximum stereo power dissipation without exceeding the maximum junction temperature is approximately
113°C for the KTW package.
113°C for the KTW package.
T
JMAX
= P
DMAX-SE
θ
JA
+ T
A
(4)
gives the maximum junction temperature T
JMAX
. If the result violates the LM4940's 150°C, reduce the
maximum junction temperature by reducing the power supply voltage or increasing the load resistance. Further
allowance should be made for increased ambient temperatures.
allowance should be made for increased ambient temperatures.
The above examples assume that a device is operating around the maximum power dissipation point. Since
internal power dissipation is a function of output power, higher ambient temperatures are allowed as output
power or duty cycle decreases.
internal power dissipation is a function of output power, higher ambient temperatures are allowed as output
power or duty cycle decreases.
If the result of
is greater than that of
, then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. Further, ensure that speakers rated at a nominal 4
Ω
do not fall
below 3
Ω
. If these measures are insufficient, a heat sink can be added to reduce
θ
JA
. The heat sink can be
created using additional copper area around the package, with connections to the ground pins, supply pin and
amplifier output pins. Refer to the
amplifier output pins. Refer to the
curves for power dissipation
information at lower output power levels.
POWER SUPPLY VOLTAGE LIMITS
Continuous proper operation is ensured by never exceeding the voltage applied to any pin, with respect to
ground, as listed in the
ground, as listed in the
section.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection. Applications that employ a voltage regulator typically use a 10µF in parallel with a 0.1µF filter
capacitors to stabilize the regulator's output, reduce noise on the supply line, and improve the supply's transient
response. However, their presence does not eliminate the need for a local 1.0µF tantalum bypass capacitance
connected between the LM4940's supply pins and ground. Do not substitute a ceramic capacitor for the
tantalum. Doing so may cause oscillation. Keep the length of leads and traces that connect capacitors between
the LM4940's power supply pin and ground as short as possible. Connecting a 10µF capacitor, C
rejection. Applications that employ a voltage regulator typically use a 10µF in parallel with a 0.1µF filter
capacitors to stabilize the regulator's output, reduce noise on the supply line, and improve the supply's transient
response. However, their presence does not eliminate the need for a local 1.0µF tantalum bypass capacitance
connected between the LM4940's supply pins and ground. Do not substitute a ceramic capacitor for the
tantalum. Doing so may cause oscillation. Keep the length of leads and traces that connect capacitors between
the LM4940's power supply pin and ground as short as possible. Connecting a 10µF capacitor, C
BYPASS
, between
the BYPASS pin and ground improves the internal bias voltage's stability and improves the amplifier's PSRR.
The PSRR improvements increase as the bypass pin capacitor value increases. Too large, however, increases
turn-on time and can compromise the amplifier's click and pop performance. The selection of bypass capacitor
values, especially C
The PSRR improvements increase as the bypass pin capacitor value increases. Too large, however, increases
turn-on time and can compromise the amplifier's click and pop performance. The selection of bypass capacitor
values, especially C
BYPASS
, depends on desired PSRR requirements, click and pop performance (as explained in
the section,
), system cost, and size constraints.
MICRO-POWER SHUTDOWN
The LM4940 features an active-low shutdown mode that disables the amplifier's bias circuitry, reducing the
supply current to 40
supply current to 40
μ
A (typ). Connect SHUTDOWN to a voltage between 2V to V
DD
/2 for normal operation.
Connect SHUTDOWN to GND to disable the device. A voltage that is greater than GND can increase shutdown
current.
current.
Copyright © 2003–2013, Texas Instruments Incorporated
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