LTC1992 datasheet(37/42 Pages) AD

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LTC1992 Family

1992fb

Figure 7. Asymmetrical Feedback Application Circuits (Most Suitable in Applications with Dual,

Split Supplies (e.g., ±5V), Ground Referenced Single-Ended Input Signals and VOCM Connected to Ground)

once the VOCM voltage is set to zero, the gain formula is the

same as a standard noninverting op amp circuit multiplied

by two to account for the complementary output. Taking

RFB to zero (i.e., taking β to one) gives the same formula

as the top circuit. As in the top circuit, this circuit is also

useful as a single-ended output, high input impedance

inverting gain block (this time with gain). The input com-

mon mode considerations are similar to the top circuit’s,

but are not nearly as constrained since there is now gain

in the noninverting amplifier path. This circuit, with VOCM

at ground, also permits a rail-to-rail output swing in most

applications.

The bottom circuit is another circuit that utilizes a standard

op amp configuration with a complementary output. In this

case, the standard op amp circuit has an inverting con-

figuration. With VOCM at zero volts, the gain formula is the

same as a standard inverting op amp circuit multiplied by

two to account for the complementary output. This circuit

does not have any common mode level constraints as the

inverting input voltage sets the input common mode level.

This circuit also delivers rail-to-rail output voltage swing

without any concerns.

APPLICATIONS INFORMATION

–

+VOUT

VOUTDIFF = 2(+VIN – VOCM)

SETTING VOCM = 0V

VOUTDIFF = 2VIN

–VOUT

VIN

VOCM

VOCM LTC1992

–

+VOUT

RFB

RIN

VOUTDIFF = 2

SETTING VOCM = 0V

VOUTDIFF = 2VIN

–VOUT

VIN

VOCM

RIN

RFB

()

+VIN

;

= 2VIN 1 +

– VOCM

()1 ()

RIN

RIN + RFB

RFB

RIN

–

+VOUT

VOUTDIFF = 2

SETTING VOCM = 0V

VOUTDIFF = 2VIN

–VOUT

1992 F07

VIN

VOCM

()

+VIN

;

= 2VIN

+ VOCM

1 –

()

1 –

()

RIN

RIN + RFB

RFB

RIN

VOCM LTC1992

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