APA2057A
Application Information (Cont.)
Via diameter
=25mil X4
Power Dissipation (Cont.)
Via diameter
=15mil X10
70 mil
120 mil
180 mil
power dissipation from equation 9, assuming a 5V-
power supply and an 8W load, must not be greater than
70 mil
the power dissipation that results from the equation 9:
TJ,MAX - TA
15 mil
(10)
PD,MAX
=
qJA
For TSSOP-28 package with thermal pad, the thermal
resistance (qJA) is equal to 45oC/W.
Since the maximum junction temperature (TJ,MAX) of
APA2057A is 150°C and the ambient temperature (TA) is
defined by the power system design, the maximum power
dissipation that the IC package is able to handle can be
obtained from equation10. Once the power dissipation is
greater than the maximum limit (PD,MAX), either the supply
voltage (VDD) must be decreased, the load impedance
(RL) must be increased or the ambient temperature
should be reduced.
12mil
Exposed for thermal
PAD connected
Ground plane for
ThermalPAD
Figure 5: TSSOP-28P layout recommendation
Thermal Considerations
Thermal Pad Considerations
The thermal pad must be connected to ground. The
package with thermal pad of the APA2057A requires
special attention on thermal design. If the thermal de-
sign issues are not properly addressed, the APA2057A
4W will go into thermal shutdown when driving a 4W load.
The thermal pad on the bottom of the APA2057A 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 on
the top surface of the circuit board, 8 to 10 vias of 15 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.
Linear power amplifiers dissipate a significant amount
of heat in the package under normal operating conditions.
In the Power Dissipation vs. Output Power graph, the
APA2057A is operating at a 5V supply and a 4W speaker
that 2W output power peaks are available. The vertical
axis gives the information of power dissipation (PD) in
the IC with respect to each output driving power (PO) on
the horizontal axis.
This is valuable information when attempting to estimate
the heat dissipation of the IC requirements for the
amplifier system.
Using the power dissipation curves for a 5V/4W system,
the internal dissipation in the APA2057A and maximum
ambient temperatures is shown in Table 3.
If the ambient temperature is higher than 25°C, a larger
copper plane or forced-air cooling will be required to keep
the APA2057A junction temperature below the thermal
shutdown temperature (150°C).
Average
output
power (W) (W/channel)
Power
dissipation
Max. TA (°C)
Peak output
power (W)
With thermal pad
2
2
2
2
2
1.95
1.17
0.74
0.43
0.19
1.25
1.25
1.19
1.05
0.8
37
37
43
55
78
In higher ambient temperature, higher airflow rate and/or
larger copper area will be required to keep the IC out of
thermal shutdown. See Demo Board Circuit Layout as
an example for PCB layout.
Table 3: APA2057A Power information, 5V/4W, Stereo, Differential mode
Copyright ã ANPEC Electronics Corp.
25
www.anpec.com.tw
Rev. A.1 - Aug., 2007
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
