Datasheet
LTC6084/LTC6085
11
60845fa
APPLICATIONS INFORMATION
Figure 3. Inverting Amplifi er with Muxed Output
–
+
10k
10k
10k
10k
OUT
LTC6084
(DD PACKAGE)
SEL = 5V, OUT = –INA
SEL = 0V, OUT = –INB
10k 10k
SHDN
A
SHDN
B
FAIRCHILD
NC7SZ04 OR
EQUIVALENT
5V
A
5V
INA
5V
10k
10k
5V
60845 F03
INB
SEL
–
+
B
SHDN Pins
Pins 5 and 6 are used for power shutdown of the LTC6084
in the DD package. If they are fl oating, internal current
sources pull pins 5 and 6 to V
+
and the amplifi ers operate
normally. In shutdown the amplifi er output is high imped-
ance, and each amplifi er draws less than 1µA current.
This feature allows the part to be used in muxed output
applications as shown in Figure 3.
ESD
The LTC6084/LTC6085 has reverse-biased ESD protection
diodes on all inputs and outputs as shown in the Simpli-
fi ed Schematic. If these pins are forced beyond either
supply, unlimited current will fl ow through these diodes.
If the current is transient and limited to 100mA or less,
no damage to the device will occur.
The amplifi er input bias current is the leakage current of
these ESD diodes. This leakage is a function of the tem-
perature and common mode voltage of the amplifi er, as
shown in the Typical Performance Characteristics.
Noise
In the frequency region above 1kHz, the LTC6084/LTC6085
shows good noise voltage performance. In this region,
noise can be dominated by the total source resistance of the
particular application. Specifi cally, these amplifi ers exhibit
the noise of a 58k resistor, meaning it is desirable to keep
the source and feedback resistance at or below this value,
i.e., R
S
+ R
G
||R
FB
≤ 58k. Above this total source impedance,
the noise voltage is dominated by the resistors.
At low frequency, noise current can be estimated from the
expression i
n
= √2qI
B
, where q = 1.6 • 10
–19
coulombs.
Equating √4kTRΔf and R√2qI
B
Δf shows that for a source
resistor below 50G the amplifi er noise is dominated by
the source resistance. Noise current rises with frequency.
See the curve Input Noise Current vs Frequency in the
Typical Performance Characteristics section.