Texas Instruments 3 Channel 25W Audio Power Amplifier with Mute and Standby LM4782TABD/NOPB LM4782TABD/NOPB 데이터 시트
제품 코드
LM4782TABD/NOPB
SNAS231B – FEBRUARY 2004 – REVISED MARCH 2013
P
DMAX
= (V
CC
)
2
/ 2
π
2
R
L
(1)
Thus by knowing the total supply voltage and rated output load, the maximum power dissipation point can be
calculated. The package dissipation is three times the number which results from
calculated. The package dissipation is three times the number which results from
since there are
three amplifiers in each LM4782. Refer to the graphs of Power Dissipation versus Output Power in the
section which show the actual full range of power dissipation not just the maximum
theoretical point that results from
DETERMINING THE CORRECT HEAT SINK
The choice of a heat sink for a high-power audio amplifier is made entirely to keep the die temperature at a level
such that the thermal protection circuitry is not activated under normal circumstances.
such that the thermal protection circuitry is not activated under normal circumstances.
The thermal resistance from the die to the outside air,
θ
JA
(junction to ambient), is a combination of three thermal
resistances,
θ
JC
(junction to case),
θ
CS
(case to sink), and
θ
SA
(sink to ambient). The thermal resistance,
θ
JC
(junction to case), of the LM4782TA is 1.0°C/W. Using Thermalloy Thermacote thermal compound, the thermal
resistance,
resistance,
θ
CS
(case to sink), is about 0.2°C/W. Since convection heat flow (power dissipation) is analogous to
current flow, thermal resistance is analogous to electrical resistance, and temperature drops are analogous to
voltage drops, the power dissipation out of the LM4782 is equal to the following:
voltage drops, the power dissipation out of the LM4782 is equal to the following:
P
DMAX
= (T
JMAX
−
T
AMB
) /
θ
JA
(2)
where T
JMAX
= 150°C, T
AMB
is the system ambient temperature and
θ
JA
=
θ
JC
+
θ
CS
+
θ
SA
.
Once the maximum package power dissipation has been calculated using
, the maximum thermal
resistance,
θ
SA
, (heat sink to ambient) in °C/W for a heat sink can be calculated. This calculation is made using
which is derived by solving for
θ
SA
in
θ
SA
= [(T
JMAX
−
T
AMB
)
−
P
DMAX
(
θ
JC
+
θ
CS
)] / P
DMAX
(3)
Again it must be noted that the value of
θ
SA
is dependent upon the system designer's amplifier requirements. If
the ambient temperature that the audio amplifier is to be working under is higher than 25°C, then the thermal
resistance for the heat sink, given all other things are equal, will need to be smaller.
resistance for the heat sink, given all other things are equal, will need to be smaller.
SUPPLY BYPASSING
The LM4782 has excellent power supply rejection and does not require a regulated supply. However, to improve
system performance as well as eliminate possible oscillations, the LM4782 should have its supply leads
bypassed with low-inductance capacitors having short leads that are located close to the package terminals.
Inadequate power supply bypassing will manifest itself by a low frequency oscillation known as “motorboating” or
by high frequency instabilities. These instabilities can be eliminated through multiple bypassing utilizing a large
tantalum or electrolytic capacitor (10
system performance as well as eliminate possible oscillations, the LM4782 should have its supply leads
bypassed with low-inductance capacitors having short leads that are located close to the package terminals.
Inadequate power supply bypassing will manifest itself by a low frequency oscillation known as “motorboating” or
by high frequency instabilities. These instabilities can be eliminated through multiple bypassing utilizing a large
tantalum or electrolytic capacitor (10
μ
F or larger) which is used to absorb low frequency variations and a small
ceramic capacitor (0.1
μ
F) to prevent any high frequency feedback through the power supply lines.
If adequate bypassing is not provided, the current in the supply leads which is a rectified component of the load
current may be fed back into internal circuitry. This signal causes distortion at high frequencies requiring that the
supplies be bypassed at the package terminals. It is recommended that a ceramic 0.1
current may be fed back into internal circuitry. This signal causes distortion at high frequencies requiring that the
supplies be bypassed at the package terminals. It is recommended that a ceramic 0.1
μ
F capacitor and an
electrolytic or tantalum 10
μ
F or larger capacitor be placed as close as possible to the IC's supply pins and then
an additional electrolytic capacitor of 470
μ
F or more on each supply line.
18
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: