LT6014ACS8 datasheet(12/16 Pages) LINER

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LT6013/LT6014

60134fa

Not Unity-Gain Stable

The LT6013 and LT6014 amplifiers are optimized for the

lowest possible noise and smallest package size, and are

intentionally decompensated to be stable in a gain con-

figuration of 5 or greater. Do not connect the amplifiers in

a gain less than 5 (such as unity-gain). For a unity-gain

stable amplifier with similar performance though slightly

higher noise and lower bandwidth, see the LT6010 and

LT6011/LT6012 datasheets.

Figure 1 shows simple inverting and non-inverting op amp

configurations and indicates how to achieve a gain of 5 or

greater. For more general feedback networks, determine

the gain that the op amp “sees” as follows:

1. Suppose the op amp is removed from the circuit.

2. Apply a small-signal voltage at the output node of the

op amp.

3. Find the differential voltage that would appear across

the two inputs of the op amp.

4. The ratio of the output voltage to the input voltage is

the gain that the op amp “sees”. This ratio must be

5 or greater.

Do not place a capacitor bigger than 200pF between the

output to the inverting input unless there is a 5 times larger

capacitor from that input to AC ground. Otherwise, the op

amp gain would drop to less than 5 at high frequencies,

and the stability of the loop would be compromised.

The LT6013 and LT6014 can be used in lower gain

configurations when an impedance is connected between

the op amp inputs. Figure 2 shows inverting and non-

inverting unity gain connections. The RC network across

the op amp inputs results in a large enough noise gain at

high frequencies, thereby ensuring stability. At low fre-

quencies, the capacitor is an open circuit so the DC

precision (offset and noise) remains very good.

APPLICATIO S I FOR ATIO

Figure 1. Use LT6013 and LT6014 in a Gain of 5 or Greater

VIN

VREF

NONINVERTING:

SIGNAL GAIN = 1 + RF/RG

OP AMP GAIN = 1 + RF/RG

STABLE IF 1 + RF/RG ≥ 5

60134 F01

–

VIN

UNITY-GAIN:

DO NOT USE

–

VREF

INVERTING:

SIGNAL GAIN = –RF/RG

OP AMP GAIN = 1 + RF/RG

STABLE IF 1 + RF/RG ≥ 5

VIN

–

Figure 2. Stabilizing Op Amp for Unity Gain Operation

VOUT

VIN

–

10k

2.5k

1nF

60134 F02

VOUT

VIN

–

10k

1nF

UNITY GAIN INVERTER

UNITY GAIN FOLLOWER

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