LMC6044_17 Datasheet, PDF (11/23 Pages) Texas Instruments – CMOS Quad Micropower Operational Amplifier

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LMC6044
SNOS612D – NOVEMBER 1994 – REVISED MARCH 2013
Figure 28. LMC6044 Noninverting Gain of 10 Amplifier, Compensated to Handle Capacitive Loads
In the circuit of Figure 28, R1 and C1 serve to counteract the loss of phase margin by feeding the high frequency
component of the output signal back to the amplifier's inverting input, thereby preserving phase margin in the
overall feedback loop.
Capacitive load driving capability is enhanced by using a pull up resistor to V⁺ (Figure 29). Typically, a pull up
resistor conducting 10 μA or more will significantly improve capacitive load responses. The value of the pull up
resistor must be determined based on the current sinking capability of the amplifier with respect to the desired
output swing. Open loop gain of the amplifier can also be affected by the pull up resistor (see Electrical
Characteristics).
Figure 29. Compensating for Large Capacitive Loads with a Pull Up Resistor
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
LMC6044, typically less than 2 fA, it is essential to have an excellent layout. Fortunately, 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 acceptably low, because under conditions of high humidity or dust or
contamination, the surface leakage will be appreciable.
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