OPA454 Datasheet, PDF (20/36 Pages) Texas Instruments – High-Voltage (100V), High-Current (50mA) OPERATIONAL AMPLIFIERS, G = 1 Stable

OPA454
SBOS391 – DECEMBER 2007
ENABLE AND E/D Com
If left disconnected, E/D Com is pulled near V–
(negative supply) by an internal 10µA current source.
When left floating, ENABLE is held approximately 2V
above E/D Com by an internal 1µA source. Even
though active operation of the OPA454 results when
the ENABLE and E/D Com pins are not connected, a
moderately fast, negative-going signal capacitively
coupled to the ENABLE pin can overpower the 1µA
pull-up current and cause device shutdown. This
behavior can appear as an oscillation and is
encountered first near extreme cold temperatures. If
the enable function is not used, a conservative
approach is to connect ENABLE through a 30pF
capacitor to a low impedance source. Another
alternative is the connection of an external current
source from V+ (positive supply) sufficient to hold the
enable level above the shutdown threshold. Figure 67
shows a circuit that connects ENABLE and E/D Com.
Choosing R_P to be 1MΩ with a +50V positive power
supply voltage results in I_P = 50µA.
V+
(Positive Op Amp Supply)
I_P
R_P
DVDD
(Digital Supply)
V+
-IN
E/D
5V Logic
OPA454
V_OUT
+IN
E/D Com
V-
V-
(Negative Op Amp Supply)
Figure 67. ENABLE and E/D Com
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avoided to maximize reliability. It is always best to
provide proper heat-sinking (either by a physical plate
or by airflow) to remain considerably below the
thermal shutdown threshold. For longest operational
life of the device, keep the junction temperature
below +125°C.
THERMAL PROTECTION
Figure 68 shows the thermal shutdown behavior of a
socketed OPA454 that internally dissipates 1W.
Unsoldered and in a socket, θ_JA of the DDA package
is typically +128°C/W. With the socket at +25°C, the
output stage temperature rises to the shutdown
temperature of +150°C, which triggers automatic
thermal shutdown of the device. The device remains
in thermal shutdown (output is in a high-impedance
state) until it cools to +130°C where it again is
powered. This thermal protection hysteresis feature
typically prevents the amplifier from leaving the safe
operating area, even with a direct short from the
output to ground or either supply. The rail-to-rail
supply voltage at which catastrophic breakdown
occurs is typically 135V at +25°C. However, the
absolute maximum specification is 120V, and the
OPA454 should not be allowed to exceed 120V under
any condition. Failure as a result of breakdown,
caused by spiking currents into inductive loads
(particularly with elevated supply voltage), is not
prevented by the thermal protection architecture.
40
140
20
120
V_OUT
0
100
-20
80
-40
60
-60
40
-80
V_FLAG
20
-100
0
-120
0
-20
200
400
600
800
1000
(ms)
CURRENT LIMIT
Figure 24 and Figure 48 to Figure 50 show the
current limit behavior of the OPA454. Current limiting
is accomplished by internally limiting the drive to the
output transistors. The output can supply the limited
current continuously, unless the die temperature rises
to +150°C, which initiates thermal shutdown. With
adequate heat-sinking, and use of the lowest possible
supply voltage, the OPA454 can remain in current
limit continuously without entering thermal shutdown.
Although qualification studies have shown minimal
parametric shifts induced by 400 hours of thermal
shutdown cycling, this mode of operation should be
+2.5V
10Hz Square Wave
10kW
100kW
+50V
R_P
1MW
-IN
V+
Flag
V_FLAG
V_OUT
+IN ^OPA454 _{E/D Com}
V-
-50V
V_OUT
625W
Figure 68. Thermal Shutdown
20
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