Rainbow-electronics DS1091L Uživatelský manuál stáhnout pdf (Strana 5)

Detailed Description

The DS1091L is a clock generator that is capable of

output frequencies from 130kHz to 66.6MHz over the

full automotive temperature range (-40°C to +125°C).

The device also is capable of producing a spread-

spectrum (dithered) square-wave output using four pin-

selectable dither percentages. Both center (DS1091LA)

and down (DS1091LB) dithering options are available.

The device also features two selectable dither rates.

The DS1091L is shipped from the factory programmed

to a customer-specified frequency.

Spread Spectrum

The DS1091L has the ability to reduce radiated emis-

sion peaks. The dither percentage is controlled by the

state of the SEL0 and SEL1 pins. The output frequency

can be dithered at 0%, ±1%, ±2%, and ±4%, centered

around the programmed frequency (for the DS1091LB

this can be down dithered by 0%, -2%, -4%, and -8%).

The two select pins SEL0 and SEL1 provide a means of

selecting the dither magnitudes as follows:

A triangle wave generator injects a control signal into

the master oscillator to dither its output. The dither rate

is a function of the output frequency, f

OUT

as well as the

setting of the DR pin (see the equation below). Figure 1

shows a plot of the output frequency versus time.

where n is defined in Table 2 as a function of output fre-

quency. For example, for an output frequency of

27.0MHz, the dither rate would be 13.2kHz for DR = 0

and 6.6kHz for DR = 1.

DITHER RATE

OUT

DS1091L

Automotive Temperature Range

Spread-Spectrum Econoscillator

_____________________________________________________________________ 5

Block Diagram

FACTORY-PROGRAMMED

MASTER OSCILLATOR

DITHER RATE DIVIDER

TRIANGLE WAVE GENERATOR

(DITHER %)

FACTORY-PROGRAMMED

PRESCALER

SEL0SEL1DR

OUT

GND

WHERE f

MOSC

IS THE MASTER OSCILLATOR FREQUENCY.

MOSC

DITHER

MOSC

DS1091L

Table 1.

DITHER MAGNITUDE

SEL1

LOGIC LEVEL

SEL0

LOGIC LEVEL

DS1091LA DS1091LB

0 0 No Dither No Dither

0 1 ±1% -2%

1 0 ±2% -4%

1 1 ±4% -8%

Table 2.

OUTPUT FREQUENCY f

OUT

(MHz)

OUT

(min) f

OUT

(max)

DR = LOGIC

LEVEL 1

DR = LOGIC

LEVEL 0

0.130 0.260 4 5

0.261 0.521 5 6

0.522 1.042 6 7

1.043 2.083 7 8

2.084 4.167 8 9

4.168 8.333 9 10

8.334 16.667 10 11

16.668 33.333 11 12

33.334 66.667 12 13

1 2 3 4 5 6

Automotive Temperature Range 1

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