Datasheet

OPA569
SBOS264A
16
www.ti.com
Any tendency to activate the thermal protection circuit indi-
cates excessive power dissipation or an inadequate heat
sink. For reliable, long term, continuous operation, the junc-
tion temperature should be limited to 125°C maximum. To
estimate the margin of safety in a complete design (including
heat sink), increase the ambient temperature until the ther-
mal protection is triggered. Use worst-case loading and
signal conditions. For good, long-term reliability, thermal
protection should trigger more than 25°C above the maxi-
mum expected ambient conditions of your application. This
produces a junction temperature of 125°C at the maximum
expected ambient condition.
Fast transients of large output current swings (for example
switching quickly from sourcing 2A to sinking 2A) may cause
a glitch on the Thermal Flag pin. When switching large
currents is expected, the use of extra bypass between the
supplies or a low-pass filter on the Thermal Flag pin is
recommended.
POWER DISSIPATION AND
SAFE OPERATING AREA
Power dissipation depends on power supply, signal and load
conditions. It is dominated by the power dissipation of the
output transistors. For DC signals, power dissipation is equal
to the product of output current, I
OUT
and the output voltage
across the conducting output transistor (V
S
-V
OUT
). Dissipa-
tion with AC signals is lower. Application Bulletin AB-039
(SBOA022) explains how to calculate or measure power
dissipation with unusual signals and loads and can be found
at the TI web site (www.ti.com).
Output short-circuits are particularly demanding for the am-
plifier because the full supply voltage is seen across the
conducting transistor. It is very important to note that the
temperature protection will not shut the part down in over-
temperature conditions, unless the Thermal Flag pin is con-
nected to the Enable pin; see the section on Thermal Flag.
Figure 8 shows the safe operating area at room temperature
with various heatsinking efforts. Note that the safe output
current decreases as (V
S
– V
OUT
) increases. Figure 9 shows
the safe operating area at various temperatures with the
PowerPAD being soldered to a 2 oz copper pad.
The power that can be safely dissipated in the package is
related to the ambient temperature and the heatsink design.
The PowerPAD package was specifically designed to pro-
vide excellent power dissipation, but board layout greatly
influences the heat dissipation of the package. Refer to
the “PowerPAD Thermally Enhanced Package” section for
further details.
The OPA569 has a junction-to-ambient thermal resistance
(
θ
JA
) value of 21.6°C/W when soldered to 2oz copper plane.
This value can be further decreased to 12°C/W by the
addition of forced air. Figure 10 shows the junction-to-
ambient thermal resistance of the DWP-20 package.
FIGURE 10. Junction-to-Ambient Thermal Resistance with
Various Heatsinking Efforts.
FIGURE 8. Safe Operating Area at Room Temperature.
FIGURE 9. Safe Operating Area at Various Ambient Tempera-
tures. PowerPAD soldered to a 2oz copper pad.
10
1
0.1
V
S
– V
OUT
 (V)
SAFE OPERATING AREA AT ROOM TEMPERATURE
Output Current (A)
0123456
Copper—soldered,
without forced air.
Copper—soldered,
with 150lfm airflow.
Copper—soldered,
with 500lfm airflow.
Current is limited by the
maximum output current.
Copper—soldered,
with 250lfm airflow.
10
1
0.1
V
S
– V
OUT
 (V)
SAFE OPERATING AREA AT VARIOUS
AMBIENT TEMPERATURES
Output Current (A)
0123456
T
A
= +125°C
T
A
= +85°C
T
A
= +25°C
T
A
= –40°C
T
A
= 0°C
Current is limited by
the maximum output
current.
HEATSINKING METHOD θ
JA
The part is soldered to a 2 oz copper pad under the 21.6
exposed pad.
Soldered to copper pad with forced airflow (150lfm). 15.1
Soldered to copper pad with forced airflow (250lfm). 13.2
Soldered to copper pad with forced airflow (500lfm). 12.0