ELH0101A 데이터 시트보기 (PDF) - Elantec -> Intersil

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ELH0101A

Power Operational Amplifier

Elantec -> Intersil 

ELH0101 883 8508901 2YX

Power Operational Amplifier

Applications Information

Input Voltages

The ELH0101 operational amplifier contains

JFET input devices which exhibit high reverse

breakdown voltages from gate to source or drain

This eliminates the need for input clamp diodes

so that high differential input voltages may be

applied without a large increase in input current

However neither input voltage should be allowed

to exceed the negative supply as the resultant

high current flow may destroy the unit

Exceeding the negative common-mode limit on

either input will cause a reversal of the phase to

the output and force the amplifier output to the

corresponding high or low state Exceeding the

negative common-mode limit on both inputs will

force the amplifier output to a high state In nei-

ther case does a latch occur since raising the in-

put back within the common-mode range again

puts the input stage and thus the amplifier in a

normal operating mode

Exceeding the positive common-mode limit on a

single input will not change the phase of the out-

put however if both inputs exceed the limit the

output of the amplifier will be forced to a high

state

These amplifiers will operate with the common-

mode input voltage equal to the positive supply

In fact the common-mode voltage may exceed

the positive supply by approximately 100 mV in-

dependent of supply voltage and over the full op-

erating temperature range The positive supply

may therefore be used as a reference on an input

as for example in a supply current monitor and

or limiter

With the ELH0101 there is a temptation to re-

move the bias current compensation resistor nor-

mally used on the non-inverting input of a sum-

ming amplifier Direct connection of the inputs

to ground or a low-impedance voltage source is

not recommended with supply voltages greater

than 3V The potential problem involves loss of

one supply which can cause excessive current in

the second supply Destruction of the IC could

result if the current to the inputs of the device is

not limited to less than 100 mA or if there is

much more than 1 mF bypass on the supply bus

Although difficulties can be largely avoided by

installing clamp diodes across the supply lines on

every PC board a conservative design would in-

clude enough resistance in the input lead to limit

current to 10 mA if the input lead is pulled to

either supply by internal currents This precau-

tion is by no means limited to the ELH0101

Layout Considerations

When working with circuitry capable of resolving

picoampere level signals leakage currents in cir-

cuitry external to the op amp can significantly

degrade performance High quality insulation is a

must (Kel-F and Teflon rate high) Proper clean-

ing of all insulating surfaces to remove fluxes and

other residues is also required This includes the

IC package as well as sockets and printed circuit

boards When operating in high humidity envi-

ronments or near 0 C some form of surface coat-

ing may be necessary to provide a moisture barri-

er

The effects of board leakage can be minimized by

encircling the input circuitry with a conductive

guard ring operated at a potential close to that of

the inputs

Electrostatic shielding of high impedance circuit-

ry is advisable

Error voltages can also be generated in the exter-

nal circuitry Thermocouples formed between dis-

similar metals can cause hundreds of microvolts

of error in the presence of temperature gradients

Since the ELH0101 can deliver large output cur-

rents careful attention should be paid to power

supply power supply bypassing and load cur-

rents Incorrect grounding of signal inputs and

load can cause significant errors

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