TLE2682 Datasheet, PDF (31/49 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 high-speed JFET-input amplifiers are ideal for conditioning fast signals from high-impedance sources.
When interfacing with ADCs in single-supply 5-V systems, its on board charge pump provides the negative rail
necessary for reliable operation of the JFET inputs and delivers a common-mode input voltage range that includes
ground and the positive rail. The amplifiers can also drive resistive loads to 0.000 V while sinking 25 mA.
Figure 72 shows the switched-capacitor section configured as a voltage inverter generating approximately − 5-V
supply voltage from the single 5-V supply available. Three external components are necessary: the storage
capacitors, C_IN and C_OUT, and a fast recovery Schottky diode to clamp V_OUT during start-up. The diode is necessary
because the amplifiers present a load referenced to the positive rail and tend to pull V_OUT above ground, which may
prevent the switched-capacitor section from starting (see section on pin functions). The amplifiers use the 5-V supply
for V_CC+ (pin 16) and the derived −5-V supply for V_{CC −} (pin 4). One amplifier is shown driving an ADC; the other is
driving a resistive load (see Figure 73).
RL
5V
To ADC
RF
Signal
RF
From
Preamplifier
Filter
COUT
1N4933
+
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
RF
CIN
+
RIN
Signal
From
Transducer
Shutdown
Figure 72. Switched-Capacitor Block Supplying Negative Rail for Amplifiers
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
• POST OFFICE BOX 1443 HOUSTON, TEXAS 77251−1443
31