SLOS118B - DECEMBER 1992 - REVISED AUGUST 1994
The TLE2662 offers the advantages of JFET-input operational amplifiers and rail-to-rail common-mode input voltage range with the convenience of single-supply operation. By combining a switched-capacitor voltage converter with a dual operational amplifier in a single package, Texas Instruments now gives circuit designers new options for conditioning low-level signals in single-supply systems.
The TLE2662 features two low power, high-output drive JFET-input operational amplifiers with a switched-capacitor building block. Using two external capacitors, the switched-capacitor network can be configured as a voltage inverter, generating a negative supply voltage capable of sourcing up to 100 mA. This supply functions not only as the amplifier negative rail but is also available to drive external circuitry. In this configuration, the amplifier common-mode input voltage range extends from the positive rail to below ground, providing true rail-to-rail inputs from a single supply. Furthermore, the outputs can swing to and below ground while sinking over 25 mA. This feature was previously unavailable in operational amplifier circuits. The TLE2662 operational amplifier section has output stages that can drive 100-
loads to 2.5 V from a 5-V rail. With a 10-k load, the output swing extends to 3.5 V and can include the positive rail with a pullup resistor.
This operational amplifier offers the high slew rate, wide bandwidth, and high input impedance commonly associated with JFET-input amplifiers, making the TLE2662 operational amplifier section suited for amplifying fast signals without loading the signal source. When not sourcing or sinking current into a load, the amplifier consumes only microamperes of supply current, thereby reducing the drain on and extending the life of the power supply.
The TLE2662 features a shutdown pin (FB/SD), which can be used to disable the switched capacitor section. When disabled, the voltage converter block draws less than 150 uA from the power supply. This feature, combined with the operational amplifier's low quiescent current, makes the TLE2662 a real power saver in the standby mode.
The switched-capacitor building block also provides an on-board regulator; with the addition of an external divider, a well-regulated output voltage is easily obtained. Additional filtering can be added to minimize switching noise. The internal oscillator runs at a nominal frequency of 25 kHz. This can be synchronized to an external clock signal or can be varied using an external capacitor. A 2.5-V reference is brought out to SCREF for use with the on-board regulator or external circuitry.
The TLE2662 is characterized for operation over the industrial temperature range of -40°C to 85°C. This device is available in a 16-pin wide-body surface-mount package.
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