LTC1966CMS8 datasheet(21/32 Pages) LINER

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LTC1966

sn1966 1966fas

frequency. So with AC + DC waveforms, the required

value for CAVE should be based on half of the lowest input

frequency, using the same design curves presented in

Figures 6, 8, 17 and 18.

Crest factor, which is the peak to RMS ratio of a dynamic

signal, also effects the required CAVE value. With a higher

crest factor, more of the energy in the signal is concentrated

into a smaller portion of the waveform, and the averaging

has to ride out the long lull in signal activity. For busy

waveforms, such as a sum of sine waves, ECG traces or

SCR-chopped sine waves, the required value for CAVE

should be based on the lowest fundamental input frequency

divided as such:

DESIGN

INPUT MIN

()

•–

APPLICATIO S I FOR ATIO

using the same design curves presented in Figures 6, 8,

17 and 18. For the worst case of square top pulse trains,

that are always either zero volts or the peak voltage, base

the selection on the lowest fundamental input frequency

divided by twice as much:

DESIGN

INPUT MIN

()

•–

The effects of crest factor and DC offsets are cumulative.

So for example, a 10% duty cycle pulse train from 0VPEAK

to 1VPEAK (CF = √10 = 3.16) repeating at 16.67ms (60Hz)

input is effectively only 30Hz due to the DC asymmetry and

is effectively only:

fHz

DESIGN ==

3 16

378

•.

–

for the purposes of Figures 6, 8, 17 and 18.

Figure 20. Settling Time with DC-Accurate Post Filter

Figure 19. Settling Time with Buffered Post Filter

SETTLING TIME (SEC)

0.01

0.1

100

1066 F14

C = 100

µF

C = 47

µF

C = 22

µF

C = 10

µF

C = 4.7

µF

C = 2.2

µF

C = 1.0

µF

C = 0.47

µF

C = 0.22

µF

C = 0.1

µF

SETTLING TIME (SEC)

0.01

0.1

100

1066 F20

C = 100

µF

C = 47

µF

C = 22

µF

C = 10

µF

C = 4.7

µF

C = 2.2

µF

C = 1.0

µF

C = 0.47

µF

C = 0.22

µF

C = 0.1

µF

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