Datasheet


    
 

 
SLOS327C − AUGUST 2000 − REVISED MAY 2001
21
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
crest factor and thermal considerations (continued)
Table 4. TPA0172 Power Rating, 5-V, 8-Ω Stereo
PEAK OUTPUT POWER AVERAGE OUTPUT POWER
POWER DISSIPATION
(W/Channel)
MAXIMUM AMBIENT
TEMPERATURE
2.5 W 1250 mW (3-dB crest factor) 0.55 100°C
2.5 W 1000 mW (4-dB crest factor) 0.62 94°C
2.5 W 500 mW (7-dB crest factor) 0.59 97°C
2.5 W 250 mW (10-dB crest factor) 0.53 102°C
The maximum dissipated power (P
D(max)
) is reached at a much lower output power level for an 8-Ω load than
for a 3-Ω load. As a result, use equation 11 for calculating P
D(max)
for an 8-Ω application.
P
D(max)
+
2V
2
DD
p
2
R
L
(11)
However, in the case of a 3-Ω load, the P
D(max)
occurs at a point well above the normal operating power level.
The amplifier may therefore be operated at a higher ambient temperature than required by the P
D(max)
formula
for a 3-Ω load.
The maximum ambient temperature depends on the heat sinking ability of the PCB system. The derating factor
for the PWP package is shown in the dissipation rating table. To convert this to Θ
JA
use equation 12.
Θ
JA
+
1
Derating Factor
+
1
0.022
+ 45°CńW
(12)
To calculate maximum ambient temperatures, first consider that the numbers from the dissipation graphs are
per channel so the dissipated power needs to be doubled for two channel operation. Given the maximum
allowable junction temperature (Θ
JA
) and the total internal dissipation, the maximum ambient temperature can
be calculated using equation 13. The maximum recommended junction temperature for the TPA0172 is 150°C.
The internal dissipation figures are taken from the power dissipation vs output power graphs.
T
A
Max + T
J
Max * Θ
JA
P
D
+ 150 * 45
(
0.6 2
)
+ 96°C
(
15-dB crest factor
)
(13)
NOTE:
Internal dissipation of 0.6 W is estimated for a 2-W system with 15-dB crest factor per channel.
Tables 3 and 4 show that for some applications no airflow is required to keep junction temperatures in the
specified range. The TPA0172 is designed with thermal protection that turns the device off when the junction
temperature surpasses 150°C to prevent damage to the IC. Tables 3 and 4 were calculated for maximum
listening volume without distortion. When the output level is reduced, the numbers in the table change
significantly. Also, using 8-Ω speakers significantly increases the thermal performance by increasing amplifier
efficiency.