Datasheet

OPA569
SBOS264A
15
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RAIL TO RAIL INPUT RANGE
The input common-mode voltage range of the OPA569
extends 100mV beyond the supply rails. This is achieved by
a complementary input stage with an N-channel input differ-
ential pair in parallel with a P-channel differential pair. The
N-channel input pair is active for input voltages close to the
positive rail while the P-channel input pair is active for input
voltages close to the negative rail. The transition point is
typically at (V+) – 1.3V, and there is a small transition region
around the switching point where both transistors are on. It
is important to note that the two input pairs can have offsets
of different signs and magnitudes. Therefore, as the transi-
tion point is crossed, the offset of the amplifier changes. This
offset shift accounts for the reduced common-mode rejection
ratio over the full input common-mode range.
OUTPUT PROTECTION
Reactive and EMF-generating 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 clamp diodes from the output terminal to the
power supplies, as shown in Figure 6. Schottky rectifier
diodes with a 3A or greater continuous rating are recom-
mended.
THERMAL FLAG PIN
The OPA569 has thermal sensing circuitry that provides a
warning signal when the die temperature exceeds safe limits.
Unless the Thermal Flag is connected to the Enable pin,
when this flag is triggered, the part continues to operate even
FIGURE 6. Output Protection Diode.
OPA569
Output Protection Diode
Output Protection Diode
Current
Limit
Set
R
SET
V
O
+V
12,
13
3
17,
18
–In
+In
14,
15
–V
Enable Pin
14,
15
8
5
6
Thermal
Flag Pin
Disable
On
7
AND
OPA569
FIGURE 7. Enable/Shutdown Control Using Thermal Flag Pin
and External Control Signal.
though the junction temperature exceeds 150°C. This allows
maximum usable operation in very harsh conditions but
degrades reliability. The Thermal Flag pin can be used to
provide for orderly system shutdown before failure occurs. It
can be also used to evaluate the thermal environment to
determine need for and appropriate design of a shutdown
mechanism.
The thermal flag output signal is from a CMOS logic gate that
switches from V+ to V– to indicate that the amplifier is in
thermal limit. This flag output pin can source and sink up to
25µA. The Thermal Flag pin is HIGH during normal opera-
tion. Power dissipated in the amplifier will cause the junction
temperature to rise. When the junction temperature exceeds
150°C, the Thermal Flag pin will go LOW, and remain LOW
until the amplifier has cooled to 130°C. Despite this hyster-
esis, with a method of orderly shutdown, the Thermal Flag
pin can cycle on and off, depending on load and signal
conditions. This limits the dissipation of the amplifier but may
have an undesirable effect on the load. This temperature
range exceeds the absolute maximum temperature rating
and is intended to protect the device from excessive tem-
peratures that can cause damage. Brief and infrequent
excursions in this temperature range are likely to be toler-
ated, but are not recommended.
It is possible to connect the Thermal Flag pin directly to the
Enable pin for automatic shutdown protection. When both
thermal shutdown and the amplifier enable/disable functions
are desired, the externally generated control signal and the
Thermal Flag pin outputs should be combined with an AND
gate, as shown on Figure 7. The temperature protection was
designed to protect against overload conditions. It was not
intended to replace proper heatsinking. Continuously running
the OPA569 in and out of thermal shutdown will degrade
reliability.