APA0710/0711
Application Descriptions (Cont.)
BTL Amplifier Efficiency (Cont.)
thermal pad, the thermal resistance (qJA) is equal to
50oC/W and 160oC/W, respectively.
power supply is almost 1.5W.
Since the maximum junction temperature (TJ,MAX) of
APA0710/1 are 170oC and the ambient temperature
(TA) is defined by the power system design, the
maximum power dissipation which the IC package is
ableto handlecan be obtainedfrom equation13. Once
the power dissipation is greater than the maximum
limit (PD,MAX), either the supply voltage (VDD) must be
decreased, theload impedance (RL) must be increased
or the ambient temperature should be reduced.
Afinal point toremember about linearamplifiers(either
SE or BTL) is how to manipulate the terms in the
efficiency equation to utmost advantage when
possible. Note that in equation10, VDD is in the
denominator.
This indicates that as VDD goes down, efficiency goes
up. Inother words, usetheefficiency analysistochoose
the correct supply voltage and speaker impedance for
the application.
Thermal Pad Considerations
Power Dissipation
The thermal pad must be connected to ground. The
package with thermal pad of the APA0710/1 requires
special attention on thermal design. If the thermal
design issues are not properly addressed, the
APA0710/1 8W will go into thermal shutdown when
driving a 8W load.
Whether the power amplifier is operated in BTLor SE
modes, power dissipation is a major concern. In
equation11 states the maximum power dissipation
point for a SE mode operating at a given supply
voltage and driving a specified load.
2
VDD
SE mode : PD,MAX=
(11)
2p2RL
The thermal pad on the bottom of the APA0710/1
should be soldered down to a copper pad on the
circuit board. Heat can be conducted away from the
thermal pad through the copper plane to ambient. If
the copper plane is not onthe top surface of the circuit
board, 6 to 10 vias of 12 mil or smaller in diameter
should be used to thermally couple the thermal pad to
the bottom plane. For good thermal conduction, the
vias must be plated through and solder filled. The
copper plane used to conduct heat away from the
thermal pad should be as large as practical.
In BTL mode operation, the output voltage swing is
doubled as in SE mode. Thus the maximum power
dissipationpoint for aBTLmode operatingat thesame
given conditions is 4 times as in SE mode.
2
4VDD
BTL mode : PD,MAX=
(12)
2p2RL
Since the APA0710/1 is a mono channel power
amplifier, the maximum internal power dissipation is
equal tothe both of equations depending onthe mode
of operation. Even with this substantial increase in
power dissipation, the APA0710/1 does not require
extraheatsink. Thepowerdissipationfrom equation12,
assuming a 5V-power supply and an 8W load, must
not be greater than the power dissipation that results
from the equation13 :
If the ambient temperatureishigher than25°C, a larger
copper plane or forced-air cooling will be required to
keep the APA0710/1 junction temperature below the
thermal shutdown temperature (170°C).
In higher ambient temperature, higher airflow rate
and/or larger copper area will be required to keep the
IC out of thermal shutdown.
TJ,MAX - TA
(13)
PD,MAX=
qJA
For MSOP-8-P package with and SOP-8 without
Copyright ã ANPEC Electronics Corp.
Rev. A.5 - Oct., 2005
24
www.anpec.com.tw
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
