OPA690 datasheet(19/33 Pages) TI2

19 / 33 page

OPA699

SBOS261D

www.ti.com

The circuit operates as follows. When the input voltage is

less than VHL then the output is limiting at VH. When the input

is greater than VHH, then the output is limiting at VL, with VHL

and VHH defined as the following:

HL HH

REF

OUT

=×









+×









Due to the inverting function realized by the Schmitt Trigger,

VHL corresponds to VOUT = VH, and VHH corresponds to

VOUT = VL.

Figure 11 shows the Schmitt Trigger operating with VREF =

+5V. This gives us VHH = 2.4V and VHL = 1.6V. The propa-

gation delay for the OPA699 in a Schmitt Trigger configura-

tion is 4ns from high-to-low, and 4ns from low-to-high.

OPERATING SUGGESTIONS

THEORY OF OPERATION

The OPA699 is a voltage-feedback, gain of +4V/V stable op

amp. The output voltage is limited to a range set by the

voltage on the limiter pins (5 and 8). When the input tries to

overdrive the output, the limiters take control of the output

buffer. This action from the limiters avoids saturating any part

of the signal path, giving quick overdrive recovery and

excellent limiter accuracy at any signal gain. The limiters

have a very sharp transition from the linear region of opera-

tion to output limiting. This transition allows the limiter volt-

ages to be set very near (< 100mV) the desired signal range.

The distortion performance is also very good near the limiter

voltages.

OUTPUT LIMITERS

The output voltage is linearly dependent on the input(s) when

it is between the limiter voltages VH (pin 8) and VL (pin 5).

When the output tries to exceed VH or VL, the corresponding

limiter buffer takes control of the output voltage and holds it

at VH or VL. Because the limiters act on the output, their

accuracy does not change with the gain. The transition from

the linear region of operation to output limiting is very

sharp—the desired output signal can safely come to within

30mV of VH or VL with no onset of non-linearity. The limiter

voltages can be set to within 0.7V of the supplies (VL ≥ –VS

+ 0.7V, VH ≤ +VS – 0.7V). They must also be at least 400mV

apart (VH – VL ≥ 0.4V). When pins 5 and 8 are left open, VH

and VL go to the default voltage limit; the minimum values are

given in the electrical specifications. Looking at Figure 12 for

the zero bias current case shows the expected range of

(VS – default limit voltages) = headroom.

DESIGN-IN TOOLS

DEMONSTRATION FIXTURE

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

evaluation of circuit performance using the OPA699. The

fixture is offered free of charge as an unpopulated PCB,

delivered with user's guide. The summary information for this

fixture is shown in Table I.

Time (10ns/div)

–1

–2

–3

–4

OUT

Limiter Headroom (V)

1.0

0.5

4.0

4.5

3.5

3.0

2.5

2.0

1.5

5.0

100

–25

–50

–75

–100

Maximum Over Temperature

Minimum Over Temperature

Limiter Headroom = +V

S – VH

L – (–VS)

Current = I

VH or –IVL

FIGURE 11. Schmitt Trigger Time Domain Response for a

10MHz Sinewave.

ORDERING

LITERATURE

PRODUCT

PACKAGE

NUMBER

OPA699ID

SO-8

DEM-OPA-SO-1A

SBOU009

TABLE I. Demonstration Fixture.

FIGURE 12. Limiter Bias Current vs Bias Voltage.

The demonstration fixture can be requested at the Texas

Instruments web site (www.ti.com) through the OPA699

product folder.

OPA690 Datasheet(PDF) 19 Page - Texas Instruments

OPA690 Datasheet(HTML) 19 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

Datasheet Download

Link URL