TLE2682 Datasheet, PDF (36/49 Pages) Texas Instruments – HIGH-SPEED JFET-INPUT DUAL OPERATIONAL AMPLIFIER WITH SWITCHED-CAPACITOR VOLTAGE CONVERTER

TLE2682
HIGHĆSPEED JFETĆINPUT DUAL OPERATIONAL AMPLIFIER
WITH SWITCHEDĆCAPACITOR VOLTAGE CONVERTER
SLOS127 − JUNE 1993
APPLICATION INFORMATION
Even with filtering, switching noise is coupled into the amplifier’s signal path through ground. An example of this is
shown in Figure 87 and Figure 88. This cannot be avoided. In systems where high-precision measurement is
necessary, the shutdown pin, FB/SD, can be used to temporarily disable the switched-capacitor section while a
measurement is being taken.
VOL+ 20
VOL+ 15
VOL+ 10
RIPPLE AND SWITCHING NOISE ON
AMPLIFIER OUTPUT
vs
TIME
VCC+ = 5 V
RL = 600 Ω
CIN = 100 µF
COUT = 100 µF
Without Filter
VOL+ 5
VOL
VOL− 5
VOL+ 20
VOL+ 15
VOL+ 10
RIPPLE AND SWITCHING NOISE ON
AMPLIFIER OUTPUT
vs
TIME
VCC+ = 5 V
RL = 600 Ω
CIN = 100 µF
COUT = 100 µF
Filter:
LF = 50 µH
CF = 220 µF
See Figure 78
VOL+ 5
VOL
VOL− 5
VOL− 10
VOL− 10
VOL− 15
VOL− 15
VOL− 20
0 10 20 30 40 50 60 70 80 90 100
t − Time − µs
Figure 87
VOL− 20
0 10 20 30 40 50 60 70 80 90 100
t − Time − µs
Figure 88
By applying a voltage of less than 0.45 V to FB/SD, the internal switches are set to dump any remaining charge onto
C_OUT. The voltage at V_OUT decays to zero at a rate dependent on both the size of C_OUT and loading. During this time,
the amplifier’s outputs are free of any switching-induced ripple and noise. Figure 89 and Figure 90 show the decay
and charge times of the negative supply when the amplifier is driving a 100-Ω load.
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