Detailed description, Block diagram, Table 1 – Rainbow Electronics DS1091L User Manual
Page 5: Table 2

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
f
OUT
n
=
2
DS1091L
Automotive Temperature Range
Spread-Spectrum Econoscillator
_____________________________________________________________________
5
Block Diagram
FACTORY-PROGRAMMED
MASTER OSCILLATOR
DITHER RATE DIVIDER
TRIANGLE WAVE GENERATOR
(DITHER %)
FACTOR
Y-
PROGRAMMED
PRESCALER
SEL0
SEL1
DR
OUT
f
OUT
V
CC
V
CC
GND
WHERE
f
MOSC
IS THE MASTER OSCILLATOR FREQUENCY.
f
MOSC
f
DITHER
f
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)
n
f
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