OPA692 datasheet(21/31 Pages) BURR-BROWN

21 / 31 page

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DESIGN-IN TOOLS

DEMONSTRATION BOARDS

OPERATING SUGGESTIONS

GAIN SETTING

OUTPUT CURRENT AND VOLTAGE

DRIVING CAPACITIVE LOADS

OPA3693

SBOS353 – DECEMBER 2006

show the zero-voltage output current limit and the

zero-current output voltage limit, respectively. The

four quadrants give a more detailed view of the

OPA3693 output drive capabilities, noting that the

graph is bounded by a Safe Operating Area of 1W

A printed circuit board (PCB) is available to assist in

maximum internal power dissipation. Superimposing

the initial evaluation of circuit performance using the

resistor load lines onto the plot shows that the

OPA3693. The fixture is offered free of charge as an

OPA3693 can drive

±3.4V into 20Ω or ±3.7V into

unpopulated PCB, delivered with a user's guide. The

Ω without exceeding either the output capabilities

summary information for this fixture is shown in

or the 1W dissipation limit. A 100

Ω load line (the

Table 2.

standard test-circuit load) shows full

±3.8V output

swing

capability,

shown

the

Typical

Table 2. Demonstration Fixture

Characteristics.

ORDERING

LITERATURE

PRODUCT

PACKAGE

NUMBER

The minimum specified output voltage and current

OPA3693IDBQ,

specifications

over

temperature

are

set

SSOP-16

DEM-OPA-SSOP-3C

SBOU047

Noninverting

worst-case simulations at the cold temperature

OPA3693IDBQ,

SSOP-16

DEM-OPA-SSOP-3D

SBOU046

extreme. Only at cold startup will the output current

Inverting

and voltage decrease to the numbers shown in the

over-temperature min/max specifications. As the

The demonstration fixture can be requested at the

output

transistors

deliver

power,

their

junction

Texas Instruments web site (www.ti.com) through the

temperatures increase, which decreases their VBEs

OPA3693 product folder.

(increasing the available output voltage swing) and

increases

their

current

gains

(increasing

the

available output current). In steady-state operation,

the available output voltage and current is always

greater than that shown in the over-temperature

characteristics

since

the

output

stage

junction

Setting the gain for the OPA3693 is very easy. For a

temperatures are higher than the minimum specified

gain of +2, ground the –IN pin and drive the +IN pin

operating ambient.

with the signal. For a gain of +1, either leave the –IN

pin open and drive the +IN pin or drive both the +IN

To maintain maximum output stage linearity, no

and –IN pins (see Figure 47). For a gain of –1,

output

short-circuit

protection

provided.

This

ground the +IN pin and drive the –IN pin with the

configuration is not normally a problem, since most

input signal. An external resistor may be used in

applications include a series matching resistor at the

series with the –IN pin to reduce the gain. However,

output that limits the internal power dissipation if the

because the internal resistors (RF and RG) have a

output side of this resistor is shorted to ground.

tolerance and temperature drift different than the

However, shorting the output pin directly to an

external resistor, the absolute gain accuracy and

adjacent positive power-supply pin, in most cases,

gain drift over temperature are relatively poor

destroys the amplifier. If additional protection to a

compared to the previously described standard gain

power-supply short is required, consider a small

connections using no external resistor.

series resistor in the power-supply leads. Under

heavy output loads, this reduces the available output

voltage swing. A 5

Ω series resistor in each supply

lead limits the internal power dissipation to < 1W for

The OPA3693 provides output voltage and current

an output short while decreasing the available output

capabilities that can easily support multiple video

voltage swing only 0.5V, for up to 100mA desired

loads and/or 100

Ω loads with very low distortion.

load currents. Always place the 0.1

µF power-supply

Under no-load conditions at +25

°C, the output

decoupling capacitors after these supply-current

voltage typically swings to 1V of either supply rail;

limiting resistors directly on the device supply pins.

the tested swing limit is within 1.2V of either rail. Into

a 15

Ω load (the minimum tested load), it is tested to

deliver more than

±90mA.

One of the most demanding, and yet very common,

The specifications described above, though familiar

load conditions for an op amp is capacitive loading.

in the industry, consider voltage and current limits

Often, the capacitive load is the input of an

separately. In many applications, it is the voltage

analog-to-digital

converter

(ADC),

including

current, or V-I product, which is more relevant to

additional

external

capacitance,

which

may

circuit operation. Refer to the Output Voltage and

recommended

improve

ADC

linearity.

Current Limitations plot (Figure 21) in the Typical

high-speed, high open-loop gain amplifier like the

Characteristics. The X- and Y-axes of this graph

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