Datasheet

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