LT1637CS8 datasheet(9/12 Pages) LINER

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LT1637

APPLICATIO S I FOR ATIO

A Schottky diode in the collector of each NPN transistor of

the NPN input stage allows the LT1637 to operate with

either or both of its inputs above V+. At about 0.3V above

V+ the NPN input transistor is fully saturated and the input

bias current is typically 23

µA at room temperature. The

input offset voltage is typically 600

µV when operating

above V+. The LT1637 will operate with its input 44V above

V– regardless of V+.

The inputs are protected against excursions as much as

22V below V – by an internal 1.3k resistor in series with

each input and a diode from the input to the negative

supply. There is no output phase reversal for inputs up to

5V below V –. There are no clamping diodes between the

inputs and the maximum differential input voltage is 44V.

Output

The output voltage swing of the LT1637 is affected by

input overdrive as shown in the typical performance

curves. When monitoring input voltages within 100mV of

V+, gain should be taken to keep the output from clipping.

The output of the LT1637 can be pulled up to 25V beyond

V+ with less than 1nA of leakage current, provided that V+

is less than 0.5V.

The normally reverse biased substrate diode from the

output to V– will cause unlimited currents to flow when the

output is forced below V–. If the current is transient and

limited to 100mA, no damage will occur.

The LT1637 is internally compensated to drive at least

200pF 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 4700pF, at all

output currents.

Distortion

There are two main contributors of distortion in op amps:

output crossover distortion as the output transitions from

sourcing to sinking current and distortion caused by

nonlinear common mode rejection. Of course, if the op

amp is operating inverting there is no common mode

induced distortion. When the LT1637 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 LT1637 should be

operated single supply, with the output always sourcing

current and with the input voltage swing between ground

and (V+ – 0.9V). See the Typical Performance Character-

istics curves.

Gain

The open-loop gain is less sensitive to load resistance

when the output is sourcing current. This optimizes per-

formance in single supply applications where the load is

returned to ground. The typical performance photo of

Open-Loop Gain for various loads shows the details.

Shutdown

The LT1637 can be shut down two ways: using the

shutdown pin or bringing V+ to within 0.5V of V–. When V+

is brought to within 0.5V of V– both the supply current and

output leakage current drop to less than 10nA. When the

shutdown pin is brought 1.2V above V –, the supply

current drops to about 3

µA and the output leakage current

is less than 1

µA,independentofV+.Ineithercasetheinput

bias current is less than 0.1nA (even if the inputs are 44V

above the negative supply).

The shutdown pin can be taken up to 32V above V –. The

shutdown pin can be driven below V –, however the pin

current through the substrate diode should be limited with

an external resistor to less than 10mA.

Input Offset Nulling

The input offset voltage can be nulled by placing a 10k

potentiometer between Pins 1 and 8 with its wiper to V–

(see Figure 1). The null range will be at least

±3mV.

Figure 1. Input Offset Nulling

LT1637

10k

1637 F01

V –

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