OPA347SASLASH3K datasheet(8/21 Pages) TI

8 / 21 page

OPA347, 2347, 4347

SBOS167C

www.ti.com

COMMON-MODE REJECTION

The CMRR for the OPA347 is specified in several ways so

the best match for a given application may be used. First, the

CMRR of the device in the common-mode range below the

transition region (VCM < (V+) – 1.7V) is given. This specifica-

tion is the best indicator of the capability of the device when

the application requires use of one of the differential input

pairs. Second, the CMRR at VS = 5.5V over the entire

common-mode range is specified.

INPUT VOLTAGE

The input common-mode range extends from (V–) – 0.2V to

(V+) + 0.2V. For normal operation, inputs should be limited

to this range. The absolute maximum input voltage is 500mV

beyond the supplies. Inputs greater than the input

common-mode range but less than the maximum input

voltage, while not valid, will not cause any damage to the op

amp. Furthermore, if input current is limited the inputs may go

beyond the power supplies without phase inversion, as

shown in Figure 4, unlike some other op amps.

Normally, input currents are 0.4pA. However, large inputs

(greater than 500mV beyond the supply rails) can cause

excessive current to flow in or out of the input pins. There-

fore, as well as keeping the input voltage below the maxi-

mum rating, it is also important to limit the input current to

less than 10mA. This is easily accomplished with an input

resistor, as shown in Figure 5.

FIGURE 3. Design Optimization with Rail-to-Rail Input Op Amps.

Rail-to-rail op amps can be used in virtually any op amp

configuration. To achieve optimum performance, how-

ever, applications using these special double-input-stage

op amps may benefit from consideration of their special

behavior.

In many applications, operation remains within the com-

mon-mode range of only one differential input pair. How-

ever, some applications exercise the amplifier through the

transition region of both differential input stages. A small

discontinuity may occur in this transition. Careful selection

of the circuit configuration, signal levels, and biasing can

often avoid this transition region.

DESIGN OPTIMIZATION WITH RAIL-TO-RAIL INPUT OP AMPS

With a unity-gain buffer, for example, signals will traverse

this transition at approximately 1.3V below the V+ supply

and may exhibit a small discontinuity at this point.

The common-mode voltage of the noninverting amplifier

is equal to the input voltage. If the input signal always

remains less than the transition voltage, no discontinuity

will be created. The closed-loop gain of this configuration

can still produce a rail-to-rail output.

Inverting amplifiers have a constant common-mode volt-

age equal to VB. If this bias voltage is constant, no

discontinuity will be created. The bias voltage can gener-

ally be chosen to avoid the transition region.

FIGURE 4. OPA347—No Phase Inversion with Inputs Greater

than the Power-Supply Voltage.

V+

Noninverting Amplifier

CM = VIN

V+

Inverting Amplifier

CM = VB

V+

Unity-Gain Buffer

CM = VIN = VO

FIGURE 5. Input Current Protection for Voltages Exceeding

the Supply Voltage.

Ω

OPA347

10mA max

+5V

OUT

OVERLOAD

5.5V

–0.5V

200

µs/div

OPA347SA/3K Datasheet(PDF) 8 Page - Texas Instruments

OPA347SA/3K Datasheet(HTML) 8 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

Datasheet Download

Link URL