Datasheet

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SBOS156B − MARCH 1987 − REVISED APRIL 2008
www.ti.com
10
SAFE OPERATING AREA
Stress on the output transistors is determined both by the
output current and by the output voltage across the
conducting output transistors, V
S
− V
O
. The power
dissipated by the output transistor is equal to the product
of the output current and the voltage across the conducting
transistor, V
S
− V
O
. The Safe Operating Area (SOA curve,
Figure 6 through Figure 10) illustrates the permissible
range of voltage and current. The curves shown represent
devices soldered to a printed circuit board (PCB) with no
heat sink. Increasing printed circuit trace area or the use
of a heat sink (TO-99 package) can significantly reduce
thermal resistance (q ), resulting in increased output
current for a given output voltage (see Figure 11,
Figure 12, and the Heat Sink section).
The safe output current decreases as V
S
− V
O
increases.
Output short-circuits are a very demanding case for SOA.
A short-circuit to ground forces the full power supply
voltage (V+ or V−) across the conducting transistor and
produces a typical output current of 25mA. With ±40V
power supplies, this creates an internal dissipation of 1W.
This exceeds the maximum rating and is not
recommended. If operation in this region is unavoidable,
a heat sink is required. For further insight on SOA, consult
Application Bulletin SBOA022 (available for download at
www.ti.com).
12 510
|V
S
|
−
|V
O
|(V)
20 50 100
Output Current (mA)
T
A
=25
_
C
T
A
= 120
_
C
T
A
=85
_
C
T
A
+[(|V
S
|
−
|V
O
|) I
O
×θ
JA
]
≤
T
J
(max)
θ
JA
= 100
_
C/W
T
J
(max) = 125
_
C
100
10
1
0.1
Figure 6. DIP-8 Safe Operating Area
12 510
|V
S
|
−
|V
O
|(V)
20 50 100
100
10
1
Output Current (mA)
0.1
T
A
=25
_
C
T
A
=85
_
C
T
A
= 125
_
C
T
A
+[(|V
S
|
−
|V
O
|) I
O
×θ
JA
]
≤
T
J
(max)
θ
JA
= 200
_
C/W (No Heat−Sink)
T
J
(max) = 150
_
C
NOTE: Simple clip−on heat−sinks can
reduce
θ
by as much as 50
_
C/W.
Figure 7. TO-99 Safe Operating Area
12 510
|V
S
|
−
|V
O
|(V)
20 50 100
100
10
1
Output Current (mA)
0.1
T
A
=85
_
C
T
A
= 120
_
C
T
A
+[(|V
S
|
−
|V
O
|) I
O
×θ
JA
]
≤
T
J
(max)
θ
JA
= 150
_
C/W
T
J
(max) = 125
_
C
T
A
=25
_
C
Figure 8. SO-8 (non PowerPAD) Safe Operating
Area
110
|V
S
|
−
|V
O
|(V)
100
100
10
1
Output Current (mA)
0.1
T
A
=25
_
C
T
A
=85
_
C
T
A
=120
_
C
T
A
+[(|V
S
|
−
|V
O
|) I
O
×θ
JA
]
≤
T
J
(max)
θ
JA
=96
_
C/W
T
J
(max) = 125
_
C
Figure 9. SO-8 PowerPAD Safe Operating Area
(no heat-spreader, no airflow)