DESIGN-IN TOOLS

DEMONSTRATION BOARDS

OPERATING SUGGESTIONS

GAIN SETTING

OUTPUT CURRENT AND VOLTAGE

DRIVING CAPACITIVE LOADS

OPA3693

www.ti.com ............................................................................................................................................ SBOS353A – DECEMBER 2006 – REVISED AUGUST 2008

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 20

Ω or ±3.7V into 50Ω

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

without exceeding either the output capabilities or the

summary information for this fixture is shown in

1W dissipation limit. A 100

Ω load line (the standard

Table 2.

test-circuit load) shows full ±3.8V output swing

capability, as shown in the Typical Characteristics.

Table 2. Demonstration Fixture

ORDERING

LITERATURE

The minimum specified output voltage and current

PRODUCT

PACKAGE

NUMBER

NUMBER

specifications over temperature are set by worst-case

OPA3693IDBQ,

simulations at the cold temperature extreme. Only at

SSOP-16

DEM-OPA-SSOP-3C

SBOU047

Noninverting

cold startup will the output current and voltage

OPA3693IDBQ,

SSOP-16

DEM-OPA-SSOP-3D

SBOU046

decrease

to

the

numbers

shown

in

the

Inverting

over-temperature min/max

specifications.

As

the

output

transistors

deliver

power,

their

junction

The demonstration fixture can be requested at the

temperatures increase, which decreases their VBEs

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

(increasing the available output voltage swing) and

OPA3693 product folder.

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

temperatures are higher than the minimum specified

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

operating ambient.

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

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

To maintain maximum output stage linearity, no

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

output

short-circuit

protection

is

provided.

This

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

configuration is not normally a problem, since most

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

applications include a series matching resistor at the

input signal. An external resistor may be used in

output that limits the internal power dissipation if the

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

output side of this resistor is shorted to ground.

because the internal resistors (RF and RG) have a

However, shorting the output pin directly to an

tolerance and temperature drift different than the

adjacent positive power-supply pin, in most cases,

external resistor, the absolute gain accuracy and gain

destroys the amplifier. If additional protection to a

drift over temperature are relatively poor compared to

power-supply short is required, consider a small

the previously described standard gain connections

series resistor in the power-supply leads. Under

using no external resistor.

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

an output short while decreasing the available output

The OPA3693 provides output voltage and current

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

capabilities that can easily support multiple video

load currents. Always place the 0.1

µF power-supply

loads and/or 100

Ω loads with very low distortion.

decoupling

capacitors

after

these

supply-current

Under no-load conditions at +25°C, the output voltage

limiting resistors directly on the device supply pins.

typically swings to 1V of either supply rail; 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,

load conditions for an op amp is capacitive loading.

The specifications described above, though familiar in

Often, the capacitive load is the input of an

the industry, consider voltage and current limits

analog-to-digital converter (ADC), including additional

separately. In many applications, it is the voltage ×

external capacitance, which may be recommended to

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

improve ADC linearity. A high-speed, high open-loop

circuit operation. Refer to the Output Voltage and

gain amplifier like

the

OPA3693

can

be

very

Current Limitations plot (Figure 21) in the Typical

susceptible to decreased stability and may give

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

Copyright © 2006–2008, Texas Instruments Incorporated

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