OPA445BM Datasheet, PDF (10/25 Pages) Texas Instruments – High Voltage FET-Input OPERATIONAL AMPLIFIER

OPA445
SBOS156B − MARCH 1987 − REVISED APRIL 2008
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).
100
T_A = 25_ C
10
T_A = 120_ C
T_A = 85_C
1
T_A + [(|V_S| − |V_O|) I_O × θ_JA] ≤ T_J (max)
θ_JA = 100_C/W
T_J (max) = 125_C
0.1
1
2
5
10
20
|V_S| − |V_O| (V)
50
100
Figure 6. DIP-8 Safe Operating Area
www.ti.com
100
T_A = 25_C
10
T_A = 125_ C
T_A = 85_ C
1 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.
0.1
1
2
5
10
20
|V_S| − |V_O| (V)
50
100
Figure 7. TO-99 Safe Operating Area
100
T_A = 25_C
10
T_A = 120_C
T_A = 85_ C
1
0.1
1
T_A + [(|V_S| − |V_O|) I_O ×
θ_JA = 150_C/W
T_J (max) = 125_C
2
5
θ_JA] ≤
10
T_J (max)
20
|V_S| − |V_O| (V)
50
100
Figure 8. SO-8 (non PowerPAD) Safe Operating
Area
100
T_A = 25_ C
10
T_A = 120_C
T_A = 85_C
1
T_A + [(|V_S| − |V_O|) I_O × θ_JA] ≤ T_J (max)
θ _JA = 96_ C/W
T_J (max) = 125_C
0.1
1
10
100
|V_S| − |V_O| (V)
Figure 9. SO-8 PowerPAD Safe Operating Area
(no heat-spreader, no airflow)
10