TLE2682 Datasheet, PDF (37/49 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
OFF-STATE VOLTAGE DECAY
AT SWITCHED-CAPACITOR OUTPUT
vs
TIME
3
VCC+ = 5 V
2
VCC _− = VOUT
CIN = 100 µF
RL = 100 Ω
1
VID = − 100 mV
COUT = 22 µF
0
TURN-ON VOLTAGE RISE
AT SWITCHED-CAPACITOR OUTPUT
vs
TIME
3
VCC+ = 5 V
2
VCC _− = VOUT
CIN = 100 µF
1
RL = 100 Ω
VID = − 100 mV
COUT = 22 µF
0
−1
−1
−2
−2
−3
−3
−4
−4
−5
0
10 20 30 40 50 60 70 80
t − Time − ms
Figure 89
−5
0 12 3 4 56 78
t − Time − ms
Figure 90
It is important to remember that the amplifier’s negative common-mode input voltage limit (V_ICR−) is specified as an
offset from the negative rail. Care should be taken to ensure that the input signal does not violate this limit as V_OUT
decays. The negative output voltage swing is similarly affected by the gradual loss of the negative rail.
This application takes advantage of the otherwise unused V_REF output of the switched-capacitor block to bias one
amplifier to 2.5 V. This is especially useful when the amplifier is followed by an ADC, keeping the signal centered in
the middle of the converter’s dynamic range. Other biasing methods may be necessary in precision systems.
In Figure 91, V_REF , R1, and R2 are used to generate a feedback voltage to the TLE2682’s error amplifier. This
voltage, fed into FB/SD, is used to regulate the voltage at V_OUT, thereby further reducing output ripple. When used
this way, there is a higher voltage loss ( V_IN − |V_OUT| ) associated with the regulation. For example, the inverter
generates an unregulated voltage of approximately − 4.5 V from a positive 5-V source; it can achieve a regulated
output voltage of only about −3.5 V. Though this reduces the amplifier’s input and output dynamic range, both V_ICR−
and V_OL still extends to below ground.
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