OPA452 Datasheet, PDF (10/17 Pages) Texas Instruments – 80V, 50mA OPERATIONAL AMPLIFIERS

POWER SUPPLIES
The OPA452 and OPA453 may be operated from power
supplies of ±10V to ±40V, or a total of 80V with excellent
performance. Most behavior remains unchanged throughout
the full operating voltage range. Parameters that vary signifi-
cantly with operating voltage are shown in the Typical Char-
acteristics.
For applications that do not require symmetrical output volt-
age swing, power-supply voltages do not need to be equal.
The OPA452 and OPA453 can operate with as little as 20V
between the supplies or with up to 80V between the supplies.
For example, the positive supply could be set to 70V with the
negative supply at –10V or vice-versa.
The tabs of the DDPAK-7 and TO220 packages are electri-
cally connected to the negative supply (V–), however, these
connections should not be used to carry current. For best
thermal performance, the tab should be soldered directly to
the circuit board copper area (see Heat Sinking section).
POWER DISSIPATION
Internal power dissipation of these op amps can be quite
large. All of the specifications for the OPA452 and OPA453
may change with junction temperature. If the device is not
subjected to internal self-heating, the junction temperature
will be the same as the ambient. However, in practical
applications, the device will self-heat and the junction tem-
perature will be significantly higher than ambient. The follow-
ing calculation can be performed to establish junction tem-
perature as a function of ambient temperature and the
conditions of the application.
Consider the OPA452 in a circuit configuration where the
load is 600Ω and the output voltage is 20V. The supplies are
at ±40V and the ambient temperature (T_A) is 40°C. The θ_JA
for the package plus heat sink is 30°C/W.
First, the quiescent heating of the op amp is as follows:
P_D(internal) = I_Q • V_S = 6mA • 80V = 480mW
The output current (I_O) can be calculated:
I_O = V_O/R_L = 20V/600Ω = 33.33mA
The power being dissipated (P_D) in the output transistor of
the amplifier can be calculated:
P_{D(output stage)} = I_O • (V_S – V_O) = 33.3mA • (40 – 20) = 667mW
P_D(total) = P_D(internal) + P_{D(output stage)} = 480mW + 667mW = 1147mW
The resulting junction temperature can be calculated:
T_J = T_A + P_D θ_JA
T_J = 40°C + 1147mW • 30°C/W = 74.4°C
Where,
V_O = output voltage
V_S = supply voltage
I_O = output current
R_L = load resistance
T_J = junction temperature (°C)
T_A = ambient temperature (°C)
θ_JA = junction-to-air thermal resistance (°C/W)
To estimate the margin of safety in a complete design
(including heat sink), increase the ambient temperature until
the thermal protection is activated. Use worst-case load and
signal conditions. For good reliability, the thermal protection
should trigger more than +35°C above the maximum ex-
pected ambient condition of your application. This ensures a
maximum junction temperature of +125°C at the maximum
expected ambient condition.
Operation from a single power supply (or unbalanced power
supplies) can produce even larger power dissipation be-
cause a larger voltage can be impressed across the conduct-
ing output transistor. Consult Application Bulletin SBOA022
at www.ti.com for further information on how to calculate or
measure power dissipation.
Power dissipation can be minimized by using the lowest
possible supply voltage. For example, with a 50mA load, the
output will swing to within 5.0V of the power-supply rails.
Power supplies set to no more than 5.0V above the maxi-
mum output voltage swing required by the application will
minimize the power dissipation.
SAFE OPERATING AREA
The Safe Operating Area (SOA curves, Figure 3) shows the
permissible range of voltage and current. The safe output
current decreases as the voltage across the output transistor
(V_S – V_O) increases. For further insight on SOA, consult
Application Report SBOA022.
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
SAFE OPERATING AREA
100
50
+85°C, θ = 40
10
θ is total thermal
+85°C,θ =θ20
resistance including
junction-to-case.
1
This graph is for
+25°C,θ = 40
+25°Cθ,θ = 3
+125°C max operating
temperature.
0.1
10
80 100
| V_S | – | V_O | (V)
FIGURE 3. DDPAK-7 and TO220-7 Safe Operating Area.
10
OPA452, 453
www.ti.com
SBOS127C