LPC660

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SNOS554D – MAY 1998 – REVISED MARCH 2013

(Input pins are lifted out of PC board and soldered directly to components. All other pins connected to PC board.)

Figure 33. Air Wiring

BIAS CURRENT TESTING

The test method of Figure 34 is appropriate for bench-testing bias current with reasonable accuracy. To

understand its operation, first close switch S2 momentarily. When S2 is opened, then

(1)

Figure 34. Simple Input Bias Current Test Circuit

A suitable capacitor for C2 would be a 5 pF or 10 pF silver mica, NPO ceramic, or air-dielectric. When

determining the magnitude of I−, the leakage of the capacitor and socket must be taken into account. Switch S2

should be left shorted most of the time, or else the dielectric absorption of the capacitor C2 could cause errors.

Similarly, if S1 is shorted momentarily (while leaving S2 shorted)

(2)

where Cx is the stray capacitance at the + input.

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