Linear Technology LT6200CS6-5#TRMPBF Linear IC LT6200CS6-5#TRMPBF Fiche De Données

Codes de produits
LT6200CS6-5#TRMPBF
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LT6200/LT6200-5
LT6200-10/LT6201
20
62001ff
applicaTions inForMaTion
Amplifier Characteristics
Figure 1 shows a simplified schematic of the LT6200  
family, which has two input differential amplifiers in paral-
lel that are biased on simultaneously when the common 
mode voltage is at least 1.5V from either rail. This topology 
allows the input stage to swing from the positive supply 
voltage to the negative supply voltage. As the common 
mode voltage swings beyond V
CC 
– 1.5V, current source I
1
 
saturates and current in Q1/Q4 is zero. Feedback is main-
tained through the Q2/Q3 differential amplifier, but with 
an input g
m
 reduction of one-half. A similar effect occurs 
with I
2
 when the common mode voltage swings within 
1.5V of the negative rail. The effect of the g
m
 reduction is 
a shift in the V
OS
 as I
1
 or I
2
 saturate.
Input bias current normally flows out of the “+” and “–” 
inputs. The magnitude of this current increases when the 
input common mode voltage is within 1.5V of the negative 
rail, and only Q1/Q4 are active. The polarity of this current 
reverses when the input common mode voltage is within 
1.5V of the positive rail and only Q2/Q3 are active.
The second stage is a folded cascode and current mir-
ror that converts the input stage differential signals to a 
single ended output. Capacitor C1 reduces the unity cross  
frequency and improves the frequency stability with-
out degrading the gain bandwidth of the amplifier. The  
differential drive generator supplies current to the output 
transistors that swing from rail-to-rail.
The LT6200-5/LT6200-10 are decompensated op amps 
for higher gain applications. These amplifiers maintain 
identical DC specifications with the LT6200, but have a 
reduced Miller compensation capacitor C
M
. This results 
in a significantly higher slew rate and gain bandwidth 
product.
Input Protection
There are back-to-back diodes, D1 and D2, across the  
+ and – inputs of these amplifiers to limit the differential 
input voltage to ±0.7V. The inputs of the LT6200 family 
do not have internal resistors in series with the input 
transistors. This technique is often used to protect the 
input devices from overvoltage that causes excessive 
currents to flow. The addition of these resistors would 
significantly degrade the low noise voltage of these 
amplifiers. For instance, a 100Ω resistor in series with 
each input would generate 1.8nV/√Hz of noise, and the 
total amplifier noise voltage would rise from 0.95nV/√Hz 
to 2.03nV/√Hz. Once the input differential voltage ex-
ceeds ±0.7V, steady-state current conducted though 
the protection diodes should be limited to ±40mA. 
This implies 25Ω of protection resistance per volt of 
continuous overdrive beyond ±0.7V. The input diodes 
are rugged enough to handle transient currents due to 
amplifier slew rate overdrive or momentary clipping 
without these resistors.
DIFFERENTIAL
DRIVE 
GENERATOR
R1
R2
R3
R4
R5
Q2
Q3
Q5
Q6
Q9
Q8
Q7
Q10
Q11
Q1
Q4
I
1
I
2
D3
D2
D1
DESD2
DESD4
DESD3
DESD1
DESD5
DESD8
DESD7
DESD6
+
C
M
C1
+V
–V
+V
+V
+V
–V
–V
–V
V
+
V–
6203/04 F01
BIAS
V
SHDN
Figure 1. Simplified Schematic