Datasheet

LT6230/LT6230-10
LT6231/LT6232
18
623012fc
With the amplifier connected in a gain of A
V
≥ 2, the output
can invert with very heavy overdrive. To avoid this inver-
sion, limit the input overdrive to 0.5V beyond the power
supply rails.
ESD
The LT6230/LT6231/LT6232 have reverse-biased ESD
protection diodes on all inputs and outputs as shown in
Figure 1. If these pins are forced beyond either supply,
unlimited current will ow through these diodes. If the
current is transient and limited to one hundred milliamps
or less, no damage to the device will occur.
Noise
The noise voltage of the LT6230/LT6231/LT6232 is equiva-
lent to that of a 75Ω resistor, and for the lowest possible
noise it is desirable to keep the source and feedback resis-
tance at or below this value, i.e., R
S
+ R
G
||R
FB
≤ 75Ω. With
R
S
+ R
G
||R
FB
= 75Ω the total noise of the amplifier is:
e
N
=√(1.1nV)
2
+(1.1nV)
2
= 1.55nV/√Hz
Below this resistance value, the amplifier dominates the
noise, but in the region between 75Ω and about 3k, the
noise is dominated by the resistor thermal noise. As the
total resistance is further increased beyond 3k, the amplifier
noise current multiplied by the total resistance eventually
dominates the noise.
The product of e
N
• √I
SUPPLY
is an interesting way to
gauge low noise amplifiers. Most low noise amplifiers
with low eN have high I
SUPPLY
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 e
N
• √I
SUPPLY
product of
only 1.9 per amplifier, yet it is common to see amplifiers
with similar noise specifications to have e
N
• √I
SUPPLY
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 10µA maximum supply current. The ENABLE
pin must be driven low to operate the amplifier with normal
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 the Typical Performance
Characteristics.
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.
applicaTions inForMaTion