OPA569 datasheet(14/28 Pages) TI1

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OPA569

SBOS264A

www.ti.com

The accuracy of the current copy is reduced with small output

currents. An internal circuit monitors the direction of the

output current and enables the positive or the negative

current monitoring circuitry accordingly. There is an approxi-

mate 20

µs delay in the change of current direction. The

switching point is near quiescent conditions and may cause

current monitor inaccuracy with small output currents.

ENABLE PIN—OUTPUT DISABLE

The Enable pin can disable the OPA569 within microsec-

onds. When disabled, the amplifier draws less than 10

µA and

its output enters a high-impedance state that allows multi-

plexing. It is important to note that when the amplifier is

disabled, the Thermal Flag pin circuitry continues to operate.

This feature allows use of the Thermal Flag pin output to

implement thermal protection strategies. For more details,

please see the section on thermal protection.

The OPA569 Enable pin has an internal pull-up circuit, so it

does not have to be connected to the positive supply for

normal operation. To disable the amplifier, the Enable pin

must be connected to no more than (V–) + 0.8V. To enable

the amplifier, either allow the Enable pin to float or connect

it to at least (V–) + 2.5V.

The Enable 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, thus the enable/disable logic signal and the OPA569

Enable pin are referenced to the same potential. In this

configuration, the logic level and the OPA569 Enable pin can

simply be tied together. Disable occurs for voltage levels of

less than 0.8V. The OPA569 is enabled at logic levels

greater than 2.5V.

In dual-supply operation, the logic level is referenced to a

logic ground. However, the OPA569 Enable pin is still refer-

enced to V–. To disable the OPA569, the voltage level of the

logic signal needs to be level-shifted. This can be done using

an optocoupler, as shown in Figure 5.

Examples of output behavior during disabled and enabled

conditions with various load impedances are shown in the

typical characteristics section. Please note that this behavior

is a function of board layout, load impedances and bypass

strategies. For sensitive loads, the use of a low-pass filter or

other protection strategy is recommended.

ENSURING MICROCONTROLLER COMPATIBILITY

Not all microcontrollers output the same logic state after

power-up or 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) shown in Figure 5, the enable/disable

signal is applied on the cathode side of the photodiode within

the optocoupler. A logic HIGH level causes the OPA569 to

be enabled, and a logic LOW level disables the OPA569. In

configuration (b) of Figure 5, with the logic signal applied on

the anode side, a high level disables the OPA569 and a low

level enables the op amp.

RAIL TO RAIL OUTPUT RANGE

The OPA569 has a class AB output stage with common

source transistors that are used to achieve rail-to-rail output

swing. It was designed to be able to swing closer to the rail

than other existing linear amplifiers, even with high output

current levels. A quick way to estimate the output swing with

various output current requirements is by using the equation:

VSWING [typical] = 0.1 • IO

Plots of the Output Swing vs Output Current, Supply Voltage,

and Temperature are provided in the typical characteristics

section.

Optocoupler

4N38

NOTE: (1) Optional—may be required

to limit leakage current of optocoupler

at high temperatures.

Enable

V+

14,

17,

12,

(a) +5V

(b) HCT or TTL In

HCT or

TTL In

(a)

(b)

OPA569

(1)

V–

FIGURE 5. OPA569 Shutdown Configuration for Dual

Supplies.

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