TLE2682 Datasheet, PDF (46/49 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
the TLE2682 is run intermittently, this does not present a problem because the discharge time of the output
capacitor is short compared to the off time of the device. In applications where the device has to start up before
the output capacitor (C_OUT) has fully discharged, a restart pulse must be applied to FB/SD of the TLE2682.
Using the circuit shown in Figure 105, the restart signal can be either a pulse (t_p > 100 µs) or a logic high. Diode
coupling the restart signal into FB/SD allows the output voltage to rise and regulate without overshoot. The
resistor divider R3/R4 shown in Figure 105 should be chosen to provide a signal level at FB/SD of
0.7 V −1.1 V. FB/SD is also the inverting input of the TLE2682 switched-capacitor section error amplifier and,
as such, can be used to obtain a regulated output voltage.
COUT
100 µF Tantalum
+
C1
+
VOUT
R2
R1
VIN
+
2.2 µF
1
1 OUT
2
1 IN −
3
1 IN +
4
VCC _−
5
VOUT
6
VREF
7
OSC
8
VIN
16
VCC +
15
2 OUT
14
2 IN −
13
2 IN +
12
CAP −
11
GND
10
CAP +
9
FB/SD
CIN
10 µF
+ Tantalum
R3
R4
R2 = R1
VOUT
+1
VREF
− 40 mV
2
Shutdown
Restart
Where: VREF = 2.5 V Nominal
Figure 105. Basic Regulation Configuration
regulation
The error amplifier of the TLE2682 switched-capacitor section drives the npn switch to control the voltage across
the input capacitor (C_IN), which determines the output voltage. When the reference and error amplifier of the
TLE2682 is used, an external resistive divider is all that is needed to set the regulated output voltage. Figure 105
shows the basic regulator configuration and the formula for calculating the appropriate resistor values. R1
should be 20 kΩ or greater because the reference current is limited to ± 100 µA. R2 should be in the range of
100 kΩ to 300 kΩ. Frequency compensation is accomplished by adjusting the ratio of C_IN to C_OUT. For best
results, this ratio should be approximately 1 to 10. Capacitor C1, required for good load regulation, should be
0.002 µF for all output voltages.
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