Datasheet

LTC6090
15
6090fa
applicaTions inForMaTion
Figure 9. Compensated Closed Loop
Response Reduces Peaking
Slew Enhancement
The LTC6090 includes a slew enhancement circuit which
boosts the slew rate to 19V/μs making the part capable
of slewing rail-to-rail across the 140V output range in
less than 8μs. 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 10 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 11. 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
FREQUENCY (kHz)
GAIN (dB)
6090 F09
30
10
20
0
–10
10 1000100
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 450kΩ
at DC. The AC output impedance is shown in the Typical
Performance Characteristics section.
Figure 11. Multiplexer Application
Figure 10. Distortion vs Frequency for Large Output Swings
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION + NOISE (%)
6090 F10
10
0.1
1
0.01
0.001
10 100000100 1000 10000
V
S
= ±70V
A
V
= 5
R
L
= 10k
C
F
= 30pF
V
OUT
= 100V
P-P
V
OUT
= 50V
P-P
V
OUT
= 10V
P-P
6090 F11
CH1
10k
OD
OD
10k
10k 100k
10k 100k
CH2
SELECT
–
+
–
+
LTC6090
LTC6090
COM
MUX
OUT
COM