LT1016IS8 datasheet(11/20 Pages) LINER

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LT1016

APPLICATIO S I FOR ATIO

“Fuzz” on the edges is the difficulty in Figure 10. This

condition appears similar to Figure 10, but the oscillation

is more stubborn and persists well after the output has

gone low. This condition is due to stray capacitive feed-

back from the outputs to the inputs. A 3k

W input source

impedance and 3pF of stray feedback allowed this oscilla-

tion. The solution for this condition is not too difficult.

Keep source impedances as low as possible, preferably 1k

or less. Route output and input pins and components away

from each other.

The opposite of stray-caused oscillations appears in

Figure 11. Here, the output response (Trace B) badly lags

the input (Trace A). This is due to some combination of

high source impedance and stray capacitance to ground at

the input. The resulting RC forces a lagged response at the

input and output delay occurs. An RC combination of 2k

source resistance and 10pF to ground gives a 20ns time

constant—significantly longer than the LT1016’s

response time.

Keep source impedances low and mini-

mize stray input capacitance to ground.

Figure 12 shows another capacitance related problem.

Here the output does not oscillate, but the transitions are

discontinuous and relatively slow. The villain of this

situation is a large output load capacitance. This could be

caused by cable driving, excessive output lead length or

the input characteristics of the circuit being driven. In

most situations this is undesirable and may be eliminated

by buffering heavy capacitive loads. In a few circum-

stances it may not affect overall circuit operation and is

tolerable.

Consider the comparator’s output load

characteristics and their potential effect on the circuit. If

necessary, buffer the load.

2V/DIV

50ns/DIV

1016 F10

TRACE A

2V/DIV

TRACE B

2V/DIV

10ns/DIV

1016 F11

Figure 11. Stray 5pF Capacitance from

Input to Ground Causes Delay

Figure 12. Excessive Load Capacitance Forces Edge Distortion

Figure 10. 3pF Stray Capacitive Feedback

with 3k

W Source Can Cause Oscillation

2V/DIV

100ns/DIV

1016 F12

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