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Optocoupler

4N38

E/S

V+

(a) +5V

(b) HCTorTTLIn

HCTor

TTLIn

(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 100k

Ω 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

–.

Ω || 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

required

limit

leakage

current

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

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

single-supply

and

dual-supply

applications. In single-supply operation, V

– typically

equals common ground. Therefore, the shutdown

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