LMC6001AIN National Semiconductor, LMC6001AIN Datasheet - Page 9

• Manufacturer Part Number: LMC6001AIN
• Description: IC AMP ULTRA LO INPUT CURR 8-DIP
• Manufacturer: National Semiconductor

Specifications of LMC6001AIN

• Amplifier Type: General Purpose
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• Slew Rate: 1.5 V/µs
• Gain Bandwidth Product: 1.3MHz
• Current - Input Bias: 0.01pA
• Voltage - Input Offset: 350µV
• Current - Supply: 550µA
• Current - Output / Channel: 34mA
• Voltage - Supply, Single/dual (±): 4.5 V ~ 15.5 V, ±2.25 V ~ 7.75 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• -3db Bandwidth: -
• Other names: *LMC6001AIN

PRINTED-CIRCUIT-BOARD LAYOUT
FOR HIGH-IMPEDANCE WORK
It is generally recognized that any circuit which must operate
with less than 1000 pA of leakage current requires special
layout of the PC board. When one wishes to take advantage
of the ultra-low bias current of the LMC6001, typically less
than 10 fA, it is essential to have an excellent layout. Fortu-
nately, the techniques of obtaining low leakages are quite
simple. First, the user must not ignore the surface leakage of
the PC board, even though it may sometimes appear accept-
ably low, because under conditions of high humidity or dust
or contamination, the surface leakage will be appreciable.
To minimize the effect of any surface leakage, lay out a ring
of foil completely surrounding the LMC6001's inputs and the
terminals of capacitors, diodes, conductors, resistors, relay
terminals, etc., connected to the op-amp's inputs, as in
4. To have a significant effect, guard rings should be placed
on both the top and bottom of the PC board. This PC foil must
then be connected to a voltage which is at the same voltage
as the amplifier inputs, since no leakage current can flow be-
tween two points at the same potential. For example, a PC
board trace-to-pad resistance of 10
considered a very large resistance, could leak 5 pA if the trace
were a 5V bus adjacent to the pad of the input.
This would cause a 500 times degradation from the
LMC6001's actual performance. If a guard ring is used and
held within 1 mV of the inputs, then the same resistance of
10
amount of leakage will degrade the extremely low input cur-
rent performance of the LMC6001. See
connections of guard rings for standard op-amp configura-
tions.
12
Ω will only cause 10 fA of leakage current. Even this small
FIGURE 4. Examples of Guard
Ring in PC Board Layout
Inverting Amplifier
12
Ω, which is normally
Figure 5
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Figure
9
The designer should be aware that when it is inappropriate to
lay out a PC board for the sake of just a few circuits, there is
another technique which is even better than a guard ring on
a PC board: Don't insert the amplifier's input pin into the board
at all, but bend it up in the air and use only air as an insulator.
Air is an excellent insulator. In this case you may have to
forego some of the advantages of PC board construction, but
the advantages are sometimes well worth the effort of using
point-to-point up-in-the-air wiring. See
(Input pins are lifted out of PC board and soldered directly to components.
All other pins connected to PC board).
Another potential source of leakage that might be overlooked
is the device package. When the LMC6001 is manufactured,
the device is always handled with conductive finger cots. This
is to assure that salts and skin oils do not cause leakage paths
on the surface of the package. We recommend that these
same precautions be adhered to, during all phases of inspec-
tion, test and assembly.
LATCHUP
CMOS devices tend to be susceptible to latchup due to their
internal parasitic SCR effects. The (I/O) input and output pins
look similar to the gate of the SCR. There is a minimum cur-
rent required to trigger the SCR gate lead. The LMC6001 is
designed to withstand 100 mA surge current on the I/O pins.
Some resistive method should be used to isolate any capac-
itance from supplying excess current to the I/O pins. In addi-
tion, like an SCR, there is a minimum holding current for any
FIGURE 5. Typical Connections of Guard Rings
Non-Inverting Amplifier
FIGURE 6. Air Wiring
Follower
Figure
6.
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