LT6231CS8 datasheet(18/24 Pages) LINER

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LT6230/LT6230-10/

LT6231/LT6232

sn623012 623012fas

APPLICATIO S I FOR ATIO

With RS + RG||RFB = 75Ω the total noise of the amplifier is:

eN=√(1.1nV)2+(1.1nV)2 = 1.55nV/√Hz

Below this resistance value, the amplifier dominates the

noise, but in the region between 75

Ω and about 3k, the

noise is dominated by the resistor thermal noise. As the

total resistance is further increased beyond 3k, the ampli-

fier noise current multiplied by the total resistance even-

tually dominates the noise.

The product of eN • √ISUPPLY is an interesting way to gauge

low noise amplifiers. Most low noise amplifiers with low

eN have high ISUPPLY current. In applications that require

low noise voltage with the lowest possible supply current,

this product can prove to be enlightening. The LT6230/

LT6231/LT6232 have an eN • √ISUPPLY product of only 1.9

per amplifier, yet it is common to see amplifiers with

similar noise specifications to have eN • √ISUPPLY as high

as 13.5.

For a complete discussion of amplifier noise, see the

LT1028 data sheet.

Enable Pin

The LT6230 includes an ENABLE pin that shuts down the

amplifier to 10

µA maximum supply current. The ENABLE

pin must be driven high to within 0.35V of V+ to shut down

the supply current. This can be accomplished with simple

gate logic; however care must be taken if the logic and the

LT6230 operate from different supplies. If this is the case,

then open drain logic can be used with a pull-up resistor

to ensure that the amplifier remains off. See Typical

Characteristic Curves.

The output leakage current when disabled is very low;

however, current can flow into the input protection diodes

D1 and D2 if the output voltage exceeds the input voltage

by a diode drop.

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