OPA561 datasheet(8/17 Pages) TI1

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OPA561

SBOS206E − DECEMBER 2001 − REVISED FEBRUARY 2007

www.ti.com

ENABLE/STATUS (E/S) PIN

The Enable/Status Pin provides two unique functions: 1)

output disable by forcing the pin LOW and 2) thermal

shutdown indication by monitoring the voltage level at the

pin. One or both of these functions can be utilized on the

same device. For normal operation (output enabled), the

E/S pin must be pulled HIGH (at least 2V above V−). A

small value capacitor connected between the E/S pin and

V− may be appropriate for noisy applications. To enable

the OPA561 permanently, the E/S pin can be tied to V+

through a 402k

Ω pull-up resistor.

Output Disable

The shutdown pin 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 logic signal and the

OPA561’s shutdown pin are referenced to the same

potential. In this configuration, the logic pin and the

OPA561 enable can simply be tied together. Shutdown

occurs for voltage levels of < 0.8V. The OPA561 is enabled

at logic levels > 2V.

In dual-supply operation, the logic pin is still referenced to

a logic ground. However, the shutdown pin of the OPA561

is still referenced to V−. To shutdown the OPA561, the

voltage level of the logic signal needs to be level shifted

using an optocoupler, as shown in Figure 3.

Optocoupler

4N38

402k

Ω

NOTE: (1) Optional

 may be required

to limit leakage current of octocoupler

at high temperatures.

E/S

V+

(a) +5V

(b) HCT or TTL In

HCT or

TTL In

(a)

(b)

OPA561

(1)

−

Figure 3. Shutdown Configuration for Dual

Supplies

To disable the output, the E/S pin is pulled LOW, no greater

than 0.8V above V−. This function can be used to conserve

power during idle periods. The typical time required to shut

down the output is 50ns. To return the output to an enabled

state, the E/S pin should be pulled to at least 2.0V above

V−. Typically, the output is enabled within 3

µs. It should be

noted that pulling the E/S pin HIGH (output enabled) does

not disable the internal thermal shutdown.

Ensuring Microcontroller Compatibility

Not all microcontrollers output the same logic state after

power-up

reset.

8051-type

microcontrollers, for

example, output logic HIGH levels on their ports while

other models power up with logic LOW levels after reset.

In configuration (a) as shown in Figure 3, the shutdown

signal is applied on the cathode side of the photodiode

within the optocoupler. A high logic level causes the

OPA561 to be enabled, and a low logic level shuts the

OPA561 down. In configuration (b) of Figure 3, with the

logic signal applied on the anode side, a high level causes

the OPA561 to shutdown and low level enables the op

amp.

OVER-CURRENT FLAG

The OPA561 features an over-current status flag (CLS,

Pin 9) that can be monitored to see if the load exceeds the

current limit. The output signal of the over current limit flag

is compatible to standard logic. The CLS signal is

referenced to V−. A voltage level of less than (V−) + 0.8V

indicates normal operation and a level of greater than (V−)

+ 2 indicates that the OPA561 is in current limit. The flag

is HIGH as long as the output of the OPA561 is in current

limit. At very low signal frequencies, typically < 1kHz, both

the upper (sourcing current) and lower current limit

(sinking current) are monitored. At frequencies > 1kHz,

due to internal circuit limitations, the flag output signal for

the upper current limit becomes delayed and shortened.

The flag signal for the lower current limit is unaffected by

this behavior. As the signal frequency increases further,

only the lower current limit (sinking current) is output on

pin 9.

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 OPA561 is intended to be driven

into current limit, an R/C network (snubber) may be

required. A snubber circuit may also enhance stability

when driving large capacitive loads (> 1000pF) or

inductive loads (motors, loads separated from the

amplifier by long cables). Typically, 3

Ω to 10Ω in series

with 0.01

µF to 0.1µF is adequate. Some variations in

circuit value may be required with certain loads.

Not Recommended for New Designs

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