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LT1996

1996f

representation of the circuit on the top. The LT1996 is

shown on the bottom configured in a precision gain of 9.1.

One of the benefits of the noninverting op amp configura-

tion is that the input impedance is extremely high. The

LT1996 maintains this benefit. Given the finite number of

available feedback resistors in the LT1996, the number of

gain configurations is also finite. The complete list of such

Hi-Z input noninverting gain configurations is shown in

Table 1. Many of these are also represented in Figure 5 in

schematic form. Note that the P-side resistor inputs have

been connected so as to match the source impedance

seen by the internal op amp inputs. Note also that gain and

noise gain are identical, for optimal precision.

Table 1. Configuring the M Pins for Simple Noninverting Gains.

The P Inputs are driven as shown in the examples on the next

page

M81, M27, M9 Connection

Gain

M81

M27

Output

1.08

Output

Grounded

1.11

Output

Float

Grounded

1.30

Output

Grounded

Output

1.32

Float

Output

Grounded

1.33

Output

Grounded

Float

1.44

Output

Grounded

3.19

Grounded

Output

3.7

Float

Grounded

Output

3.89

Grounded

Output

Float

4.21

Grounded

Output

Grounded

9.1

Grounded

Float

Output

Float

Grounded

11.8

Grounded

Output

Float

Grounded

Float

Grounded

Float

Grounded

Float

Grounded

109

Grounded

Float

118

Grounded

suggested in Figure 1: raise VREF, lower VEE, or provide

some negative VMORE.

Likewise, from the lower common mode extreme, making

the negative input more negative will raise the output

voltage, limited by VCC – 0.04V.

MIN VMORE = (VREF – VCC + 0.04V) • RG/RF

(should be negative)

Again, the additional input range calculated here is only

available provided the other remaining constraint is not

violated, the maximum voltage allowed on the pin.

The Classical Noninverting Amplifier: High Input Z

Perhaps the most common op amp configuration is the

noninverting amplifier. Figure 4 shows the textbook

Figure 4. The LT1996 as a Classical Noninverting Op Amp

APPLICATIO S I FOR ATIO

4pF

–

VIN

VOUT

VOUT = GAIN • VIN

GAIN = 1 + RF/RG

–

1996 F04

450k/81

450k/27

450k/9

450k/81

450k/27

450k/9

450k

LT1996

CLASSICAL NONINVERTING OP AMP CONFIGURATION.

YOU PROVIDE THE RESISTORS.

CLASSICAL NONINVERTING OP AMP CONFIGURATION

IMPLEMENTED WITH LT1991. RF = 45k, RG = 5.6k, GAIN = 9.1.

GAIN IS ACHIEVED BY GROUNDING, FLOATING OR FEEDING BACK

THE AVAILABLE RESISTORS TO ARRIVE AT DESIRED RF AND RG.

WE PROVIDE YOU WITH <0.1% RESISTORS.

4pF

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