Datasheet

10.0
1.0
0.1
OutputCurrent(A)
0 2
4
6 8 10 12 14 16 18 20 22 24 26
(V+) V , (V )(V)-
OUT
V
OUT
- -
SAFEOPERATINGAREAATROOMTEMPERATURE
Copper,Soldered
withoutForcedAir
Copper,Soldered
with200LFMAirflow
10.0
1.0
0.1
0.01
OutputCurrent(A)
0 2
4
6 8 10 12 14 16 18 20 22 24 26
SAFEOPERATINGAREAATVARIOUSAMBIENTTEMPERATURES
(PowerPADSoldered)
T = 40 C-
A
T =0 C
T =+25 C
T =+85 C
T =+125 C
A
A
A
A
°
°
°
°
°
(V+) V , (V )(V)-
OUT
V
OUT
- -
OPA564
SBOS372E –OCTOBER 2008– REVISED JANUARY 2011 www.ti.com
POWER DISSIPATION AND SAFE Once the heatsink area has been selected,
OPERATING AREA worst-case load conditions should be tested to ensure
proper thermal protection.
Power dissipation depends on power supply, signal,
and load conditions. For dc signals, power dissipation space
is equal to the product of output current (I
OUT
) and the
voltage across the conducting output transistor
[(V+) – V
OUT
when sourcing; V
OUT
– (V–) when
sinking]. Dissipation with ac signals is lower.
Application Bulletin AB-039, Power Amplifier Stress
and Power Handling Limitations (SBOA022, available
for download from www.ti.com) explains how to
calculate or measure power dissipation with unusual
signals and loads.
Figure 45 shows the safe operating area at room
temperature with various heatsinking efforts. Note
that the safe output current decreases as (V+) – V
OUT
or V
OUT
– (V–) increases. Figure 46 shows the safe
operating area at various temperatures with the
PowerPAD being soldered to a 2oz copper pad.
The power that can be safely dissipated in the
package is related to the ambient temperature and
Figure 45. Safe Operating Area at Room
the heatsink design. The PowerPAD package was
Temperature
specifically designed to provide excellent power
dissipation, but board layout greatly influences the
heat dissipation of the package. Refer to the
Thermally-Enhanced PowerPAD Package section for
further details.
The relationship between thermal resistance and
power dissipation can be expressed as:
T
J
= T
A
+ T
JA
T
JA
= P
D
× q
JA
Combining these equations produces:
T
J
= T
A
+ P
D
× q
JA
where:
T
J
= Junction temperature (°C)
T
A
= Ambient temperature (°C)
q
JA
= Junction-to-ambient thermal resistance (°C/W)
PowerPAD soldered to a 2oz copper pad.
P
D
= Power dissipation (W)
Figure 46. Safe Operating Area at Various
Ambient Temperatures
To determine the required heatsink area, required
power dissipation should be calculated and the
relationship between power dissipation and thermal
resistance should be considered to minimize
shutdown conditions and allow for proper long-term
operation (junction temperature of +85°C or less).
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