OPA454_16 Datasheet, PDF (21/47 Pages) Texas Instruments – High-Voltage (100-V), High-Current (50-mA) Operational Amplifiers

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OPA454
SBOS391B – DECEMBER 2007 – REVISED MARCH 2016
9.3.6 ENABLE and E/D Com
If left disconnected, E/D Com is pulled near V– (negative supply) by an internal 10-μA current source. When left
floating, ENABLE is held approximately 2 V above E/D Com by an internal 1-μA 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 1-μA pullup 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 30-pF
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 63 shows a circuit that
connects ENABLE and E/D Com. Choosing R_P to be 1 MΩ with a +50-V positive power supply voltage results in
I_P = 50 μA.
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 63. ENABLE and E/D Com
9.3.7 Current Limit
Figure 23 and Figure 47 to Figure 49 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
heatsinking, 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 must be avoided to maximize reliability. It is
always best to provide proper heatsinking (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.
9.4 Device Functional Modes
A unique mode of the OPA454 is the output disable capability. This function conserves power during idle periods
(quiescent current drops to approximately 150 µA). This disable is accomplished without disturbing the input
signal path, not only saving power but also protecting the load. This feature makes disable useful for
implementing external fault shutdown loops.
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