Datasheet

ENABLE AND E/D Com
THERMAL PROTECTION
OPA454
-IN
+IN
V-
V+
E/DCom
E/D
V
OUT
DVDD
(DigitalSupply)
5VLogic
R
P
V+
(PositiveOpAmpSupply)
V
(NegativeOpAmpSupply)
-
I
P
CURRENT LIMIT
0 800200 400 1000
(ms)
40
20
0
-120
V
(V)
OUT
-20
-40
-60
-80
-100
140
120
100
-20
V (V)
FLAG
80
60
40
20
0
600
V
OUT
V
FLAG
100kW10kW
E/DCom
-50V
+50V
V
FLAG
Flag
V
OUT
R
P
1MW
625W
+2.5V
10HzSquareWave
V
OUT
V+
-IN
+IN
V-
OPA454
OPA454
SBOS391A – DECEMBER 2007 – REVISED DECEMBER 2008 ....................................................................................................................................... www.ti.com
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
If left disconnected, E/D Com is pulled near V –
thermal shutdown threshold. For longest operational
(negative supply) by an internal 10 µ A current source.
life of the device, keep the junction temperature
When left floating, ENABLE is held approximately 2V
below +125 ° C.
above E/D Com by an internal 1 µ A 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 Figure 68 shows the thermal shutdown behavior of a
coupled to the ENABLE pin can overpower the 1 µ A socketed OPA454 that internally dissipates 1W.
pull-up current and cause device shutdown. This Unsoldered and in a socket, θ
JA
of the DDA package
behavior can appear as an oscillation and is is typically +128 ° C/W. With the socket at +25 ° C, the
encountered first near extreme cold temperatures. If output stage temperature rises to the shutdown
the enable function is not used, a conservative temperature of +150 ° C, which triggers automatic
approach is to connect ENABLE through a 30pF thermal shutdown of the device. The device remains
capacitor to a low impedance source. Another in thermal shutdown (output is in a high-impedance
alternative is the connection of an external current state) until it cools to +130 ° C where it again is
source from V+ (positive supply) sufficient to hold the powered. This thermal protection hysteresis feature
enable level above the shutdown threshold. Figure 67 typically prevents the amplifier from leaving the safe
shows a circuit that connects ENABLE and E/D Com. operating area, even with a direct short from the
Choosing R
P
to be 1M Ω with a +50V positive power output to ground or either supply. The rail-to-rail
supply voltage results in I
P
= 50 µ A. 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.
Figure 67. ENABLE and E/D Com
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 1000 hours of thermal
shutdown cycling, this mode of operation should be
Figure 68. Thermal Shutdown
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