LTC6090-5_15 Datasheet, PDF (17/26 Pages) Linear Technology – 140V CMOS Rail-to-Rail Output, Picoamp Input Current Op Amp

Applications Information
Slew Enhancement
The LTC6090 includes a slew enhancement circuit which
boosts the slew rate to 21V/μs making the part capable
of slewing rail-to-rail across the 140V output range in
less than 7μs. To optimize the slew rate and minimize
settling, stray capacitance should be kept to a minimum.
A feedback capacitor reduces overshoot and nonlinearities
associated with the slew enhancement circuit. The size of
the feedback capacitor should be tailored to the specific
board, supply voltage and load conditions.
Slewing is a nonlinear behavior and will affect distortion.
The relationship between slew rate and full power band-
width is given in the relationship below.
SR = V_O • ω
Where V_O is the peak output voltage and ω is frequency in
radians. The fidelity of a large sine wave output is limited
by the slew rate. The graph in Figure 9 shows distortion
versus frequency for several output levels.
Multiplexer Application
Several LTC6090s may be arranged to act as a high volt-
age analog multiplexer as shown in Figure 10. When using
this arrangement, it is possible for the output to affect the
source on the disabled amplifier’s noninverting input. The
inverting and noninverting inputs are clamped through
resistors and back to back diodes. There is a path for
current to flow from the multiplexer output through the
disabled amplifier’s feedback resistor, and through the
inputs to the noninverting input’s source. For example, if
the enabled amplifier has a –70V output, and the disabled
amplifier has a 5V input, there is 75V across the two resis-
tors and the input pins. To keep this current below 1mA
the combined resistance of the R_IN and feedback resistor
needs to be about 75k.
The output impedance of the disabled amplifier is greater
than 10MΩ at DC. The AC output impedance is shown in
the Typical Performance Characteristics section.
LTC6090/LTC6090-5
10
V_S = ±70V
A_V = 5
R_L = 10k
1 ^{CF = 30pF}
0.1
V_OUT = 100V_P-P
0.01
V_OUT = 50V_P-P
0.001
10
V_OUT = 10V_P-P
100
1000 10000
FREQUENCY (Hz)
100000
6090 F09
Figure 9. Distortion vs Frequency for Large Output Swings
SELECT
10k
CH1
OD
+
COM
LTC6090
–
10k
100k
MUX
OUT
10k
CH2
+
OD
COM
LTC6090
–
10k
100k
6090 F10
Figure 10. Multiplexer Application
For more information www.linear.com/LTC6090
6090fd
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