OPA564 Datasheet, PDF (21/35 Pages) Texas Instruments – 1.5A, 24V, 17MHz POWER OPERATIONAL AMPLIFIER

OPA564
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CURRENT LIMIT FLAG
The OPA564 features a current limit flag (I_FLAG) that
can be monitored to determine if the load current is
operating within or exceeding the current limit set by
the user. The output signal of I_FLAG is compatible with
standard CMOS logic and is referenced to the
negative supply pin (V–). A voltage level of + 0.8V or
less with respect to V– indicates that the amplifier is
operating within the limits set by the user. A voltage
level of +2.0V or greater with respect to V– indicates
that the OPA564 is operating above (exceeds) the
current limit set by the user. See Setting the Current
Limit for proper current limit operation.
OUTPUT STAGE COMPENSATION
The complex load impedances common in power op
amp applications can cause output stage instability.
For normal operation, output compensation circuitry is
typically not required. However, if the OPA564 is
intended to be driven into current limit, an R/C
network (snubber) may be required. A snubber circuit
such as the one shown in Figure 54 may also
enhance stability when driving large capacitive loads
(greater than 1000pF) or inductive loads (for
example, motors or loads separated from the
amplifier by long cables). Typically, 3Ω to 10Ω in
series with 0.01mF to 0.1mF is adequate. Some
variations in circuit value may be required with certain
loads.
OUTPUT PROTECTION
The output structure of the OPA564 includes ESD
diodes (see Figure 43). Voltage at the OPA564
output must not be allowed to go more than 0.4V
beyond either supply rail to avoid damaging the
device. Reactive and electromagnetic field
(EMF)-generation loads can return load current to the
amplifier, causing the output voltage to exceed the
power-supply voltage. This damaging condition can
be avoided with clamping diodes from the output
terminal to the power supplies, as Figure 54 and
Figure 55 illustrate. Schottky rectifier diodes with a 3A
or greater continuous rating are recommended.
THERMAL PROTECTION
The OPA564 has thermal sensing circuitry that helps
protect the amplifier from exceeding temperature
limits. Power dissipated in the OPA564 causes the
junction temperature to rise. Internal thermal
shutdown circuitry disables the output when the die
temperature reaches the thermal shutdown
temperature limit. The OPA564 output remains shut
down until the die has cooled sufficiently; see the
Electrical Characteristics, Thermal Shutdown section.
SBOS372E – OCTOBER 2008 – REVISED JANUARY 2011
Depending on load and signal conditions, the thermal
protection circuit may cycle on and off. This cycling
limits the amplifier dissipation, but may have
undesirable effects on the load. Any tendency to
activate the thermal protection circuit indicates
excessive power dissipation or an inadequate
heatsink. For reliable, long-term, continuous
operation, with I_OUT at the maximum output of 1.5A,
the junction temperature should be limited to +85°C
maximum. Figure 44 shows the maximum output
current versus junction temperature for dc and RMS
signal outputs. To estimate the margin of safety in a
complete design (including heatsink), increase the
ambient temperature until the thermal protection
triggers. Use worst-case loading and signal
conditions. For good, long-term reliability, thermal
protection should trigger more than 35°C above the
maximum expected ambient condition of the
application.
The internal protection circuitry of the OPA564 was
designed to protect against overload conditions; it
was not intended to replace proper heatsinking.
Continuously running the OPA564 into thermal
shutdown degrades reliability.
MAXIMUM OUTPUT CURRENT vs JUNCTION TEMPERATURE
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
-50
Max I_OUT (dc)
Max I_OUT (RMS)
-25
0
25
50
T_J (°C)
75 100 125
Figure 44. Maximum Output Current vs Junction
Temperature
USING T_SENSE FOR MEASURING JUNCTION
TEMPERATURE
The OPA564 includes an internal diode for junction
temperature monitoring. The h-factor of this diode is
1.033. Measuring the OPA564 junction temperature
can be accomplished by connecting the T_SENSE pin to
a remote-junction temperature sensor, such as the
TMP411 (see Figure 57).
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