LTC2400CS8 datasheet(37/40 Pages) LINER

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LTC2400

TYPICAL APPLICATIONS

pick-up from the strain bearing member is largely 60Hz,

the LTC2400 will reject it. If serious high frequency noise

is present on the strain bearing member, it may be

necessary to add buffering in order to allow the use of

noise suppression.

Stable Relaxation Oscillator

for External Clock

Applications that require that the notch produced by the

LTC2400’s sinc4 filter be placed at some frequency other

than 50Hz or 60Hz require an external clock. The fre-

quency required is 2560

× the required notch frequency.

Simple relaxation oscillators built from logic gates with

hysteresis such as the 74HC14 are not stable with tem-

perature, supply voltage changes, or from device to

device.

If for example, a remote weigh scale application requires

rejection of a resonance at 11Hz, the frequency must be set

to 28.16kHz. In many instances, these frequencies could

be produced digitally with a phase lock loop or with digital

HC04

C1 MAY VARY FROM 30pF TO 4000pF

STABLE OPERATION AT HIGHER FREQUENCIES

REQUIRES VALUES OF RESISTOR TO BE REDUCED

2400 F40

100k

47k

15pF

fOUT (kHz) =

47k

15pF

9.5 • 10–6

C1(pF)

Figure 41. Stable Relaxation Low Power Oscillator for Notch Tuning

dividers, but they are too low to be produced directly by a

quartz oscillator. Quartz stability is generally not required,

as the notches are wide enough that an oscillator with

0.1% to 1% stability is adequate.

In instances where digital generation of these frequencies

is not practical due to power, space or cost limitations, and

notches in the range of 4Hz to 120Hz are required, the

circuit in Figure 41 can be used.

The frequency can be varied over this range by changing

capacitor C1 over the range of 4000pf to 30pF. For the

resistor values shown, the output frequency in kHz is

approximately 9.5e-6 divided by C1 (C1 in pF). The circuit

produces a controlled amount of hysteresis dependent

only on resistor matching and self biases itself around the

input threshold. All gates must be in the same package,

and no loads should be driven from the outputs driving

feedback paths. If there are spare gates, they can be used

in parallel with gates B and D for improved drive of

feedback paths.

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