1636 데이터 시트보기 (PDF) - Linear Technology

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1636

Over-The-Top Micropower Rail-to-Rail Input and Output Op Amp

Linear Technology 

LT1636

APPLICATIONS INFORMATION

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 LT1636 is internally compensated to drive at least

200pF of capacitance under any output loading condi-

tions. A 0.22µF 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 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 LT1636 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 LT1636 should be

operated single supply, with the output always sourcing

current and with the input voltage swing between ground

and (V+ – 0.8V). 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 LT1636 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 1nA. When the

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

current drops to about 4µA and the output leakage current

is less than 1µA, independent of V+. In either case the input

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 ±1mV.

LT1636

8

1

10k

V–

1636 F01

Figure 1. Input Offset Nulling

1636fc

11

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