Datasheet

Optocoupler
4N38
E/S
V+
(a) +5V
(b) HCTorTTLIn
HCTor
TTLIn
(a) (b)
OPA564
(1)
V-
OPA564
SBOS372E –OCTOBER 2008– REVISED JANUARY 2011 www.ti.com
ENABLE/SHUTDOWN (E/S) PIN logic signal and the OPA564 shutdown pin are
referenced to the same potential. In this configuration,
The output of the OPA564 shuts down when the E/S
the logic pin and the OPA564 enable can simply be
pin is forced low. For normal operation (output
connected together. Shutdown occurs for voltage
enabled), the E/S pin must be pulled high (at least 2V
levels of less than 0.8V. The OPA564 is enabled at
above V–). To enable the OPA564 permanently, the
logic levels greater than 2V. In dual-supply operation,
E/S pin can be left unconnected. The E/S pin has an
the logic pin remains referenced to a logic ground.
internal 100kΩ pull-up resistor. When the output is
However, the shutdown pin of the OPA564 continues
shut down, the output impedance of the OPA564 is
to be referenced to V–.
6GΩ || 120pF. The output shutdown output voltage
versus output current is shown in Figure 42. Although Thus, in a dual-supply system, to shut down the
the output is high-impedance when shut down, there OPA564 the voltage level of the logic signal must be
is still a path through the feedback network into the level-shifted by some means. One way to shift the
input stage to ground; see Figure 43. To prevent logic signal voltage level is by using an optocoupler,
damage to the OPA564, ensure that the voltage as Figure 38 shows.
across the input terminals +IN and –IN does not
exceed 0.5V, and that the current flowing through the
input terminals does not exceed 10mA when
operated beyond the supply rails, V– and V+. Refer
to the Input Protection section.
Input Protection
Electrostatic discharge (ESD) protection followed by
back-to-back diodes and input resistors (see
Figure 43) are used for input protection on the
OPA564. Exceeding the turn-on threshold of these
diodes, as in a pulse condition, can cause current to
flow through the input protection diodes because of
the finite slew rate of the amplifier. If the input current
is not limited, the back-to-back diodes and the input
devices can be destroyed. Sources of high input
current can also cause subtle damage to the
amplifier. Although the unit may still be functional,
(1) Optional; may be required to limit leakage current of
important parameters such as input offset voltage,
optocoupler at high temperatures.
drift, and noise may shift.
Figure 38. Shutdown Configuration for Dual
When using the OPA564 as a unity-gain buffer
Supplies (Using Optocoupler)
(follower), as an inverting amplifier, or in shutdown
mode, the input voltage between the input terminals
(+IN and –IN) must be limited so that the voltage To shut down the output, the E/S pin is pulled low, no
does not exceed 0.5V. This condition must be greater than 0.8V above V–. This function can be
maintained across the entire common-mode range used to conserve power during idle periods. To return
from V– to V+. If the inputs are taken above either the output to an enabled state, the E/S pin should be
supply rail, the current must be limited to 10mA pulled to at least 2.0V above V–. Figure 27 shows the
through the ESD protection diodes. During excursions typical enable and shutdown response times. It
past the rails, it is still necessary to limit the voltage should be noted that the E/S pin does not affect the
across the input terminals. If necessary, external internal thermal shutdown.
back-to-back diodes should be added between +IN
When the OPA564 will be used in applications where
and –IN to maintain the 0.5V requirement between
the device shuts down, special care should be taken
these connections.
with respect to input protection. Consider the
following two examples.
Output Shutdown
The shutdown pin (E/S) is referenced to the negative
supply (V–). Therefore, shutdown operation is slightly
different in single-supply and dual-supply
applications. In single-supply operation, V– typically
equals common ground. Therefore, the shutdown
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