9

LT1783

APPLICATIO S I FOR ATIO

input bias current is typically 80nA. Increases in tempera-

ture will cause the voltage at which operation switches

from the PNP input stage to the NPN input stage to move

untrimmed and is typically 1.8mV.

A Schottky diode in the collector of the input transistors,

along with special geometries for these NPN transistors,

allow the LT1783 to operate with either or both of its inputs

tor is fully saturated and the input bias current is typically

30

µA at room temperature. The input offset voltage is

The inputs are protected against excursions as much as

input and a diode from the input to the negative supply.

The input stage of the LT1783 incorporates phase reversal

protection to prevent the output from phase reversing for

between the inputs and the maximum differential input

voltage is 18V.

Output

The output of the LT1783 can swing to within 60mV of the

positive rail with no load and within 3mV of the negative

rail with no load. When monitoring input voltages within

60mV of the positive rail or within 3mV of the negative rail,

gain should be taken to keep the output from clipping. The

LT1783 can sink and source over 30mA at

±5V supplies,

sourcing current is reduced to 10mA at 3V total supplies

as noted in the Electrical Characteristics.

The LT1783 is internally compensated to drive at least

400pF of capacitance under any output loading condi-

tions. A 0.22

µF capacitor in series with a 150Ω resistor

between the output and ground will compensate these

amplifiers for larger capacitive loads, up to 10,000pF, at all

output currents.

Distortion

There are two main contributors to distortion in op amps:

output crossover distortion as the output transitions from

sourcing to sinking current, and distortion caused by

nonlinear common mode rejection. If the op amp is

operating inverting, there is no common mode induced

distortion. If the op amp is operating in the PNP input stage

typically 100dB. When the LT1783 switches between

input stages, there is significant nonlinearity in the CMRR.

Lower load resistance increases the output crossover

distortion but has no effect on the input stage transition

distortion. For lowest distortion, the LT1783 should be

operated single supply, with the output always sourcing

current and with the input voltage swing between ground

istics curves, “Total Harmonic Distortion + Noise vs Out-

put Voltage Amplitude.”

Gain

The open-loop gain is almost independent of load when

the output is sourcing current. This optimizes perfor-

mance in single supply applications where the load is

returned to ground. The typical performance curve of

open-loop gain for various loads shows the details.

Shutdown

The 6-lead part includes a shutdown feature that disables

the part, reducing quiescent current and making the

output high impedance. The part can be shut down by

down, the supply current is about 5

µA and the output

leakage current is less than 1

floating. See the Typical Performance Characteristics

curves, “Supply Current vs Shutdown Voltage.”