TLE2682 Datasheet, PDF (32/49 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
5V
Signal ^RIN
From
Preamplifier
Shutdown
VIN
VOUT
Voltage
Converter
FB/SD
VREF
RF
−
+
AMP1
Signal ^RIN
From
Transducer
RL
RF
−
+
AMP2
To ADC
Figure 73. Equivalent Schematic: Amplifier 1 Driving Resistive Load,
Amplifier 2 Interfacing to an ADC
Using the switched-capacitor network to generate the negative rail for the amplifiers (or other circuitry) requires
special design considerations to minimize the effects of ripple and switching noise. Using larger values for C_OUT and
selecting low-ESR capacitors reduces the ripple and noise present on V_OUT, the − 5-V rail (refer to the capacitor
section and the output ripple discussion in the switched-capacitor section). Figure 74 and Figure 75 show the
smoothing effect of changing C_OUT from 10 µF to 100 µF when V_OUT is supplying 1 mA. Figure 76 and Figure 77
demonstrate that at heavier loads the ripple and noise are more pronounced and while increasing the size of C_OUT
helps, other steps may be necessary.
RIPPLE AND SWITCHING NOISE ON
SWITCHED-CAPACITOR OUTPUT
vs
TIME
80
VCC+ = 5 V
60
IL = 1 mA
CIN = 100 µF
COUT = 10 µF
40
RIPPLE AND SWITCHING NOISE ON
SWITCHED-CAPACITOR OUTPUT
vs
TIME
20
VCC+ = 5 V
15
IL = 1 mA
CIN = 100 µF
COUT = 100 µF
10
20
5
0
0
− 20
−5
− 40
− 60
− 80
0
10 20 30 40 50 60 70 80 90 100
t − Time − µs
Figure 74
− 10
− 15
− 20
0
10 20 30 40 50 60 70 80 90 100
t − Time − µs
Figure 75
32
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