Detailed Description
The MAX31091 clock generator is capable of output fre-
quencies from 200kHz to 66.6MHz over the full automo-
tive temperature range (-40°C to +125°C). The device can
also produce a spread-spectrum (dithered) square-wave
output using four pin-selectable dither percentages. The
device also features two selectable dither rates.
The MAX31091 is shipped from the factory-programmed
to a customer-specified frequency.
Spread Spectrum
The MAX31091 can reduce radiated emission 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 pro-
grammed frequency.
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 set-
ting of the DR pin (see the equation below). Figure 1 shows
a plot of the output frequency vs. time.
OUT
n
DITHER RATE
=
where n is defined in Table 2 as a function of output
frequency. For example, for an output frequency of
27.0MHz, the dither rate would be 13.2kHz for DR = 1 and
6.6kHz for DR = 0.
Power-Up
Upon the application of power, the MAX31091 output is
held in the low state until t
PU
has elapsed. This removes
any possibility of erroneous output transitions during initial
power-up.
Figure 1A
SEL1
LOGIC LEVEL
SEL0
LOGIC LEVEL
DITHER MAGNITUDE (%)
MAX31091AUA
0 0 No dither
0 1 Q1
1 0 Q2
1 1 Q4
OUTPUT FREQUENCY
f
OUT
(MHz)
n
f
OUT
(min) f
OUT
(max)
DR = LOGIC
LEVEL 1
DR = LOGIC
LEVEL 0
0.200 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
Table 1. Dither Magnitude
Table 2. Value of n w.r.t. Output Frequency
MAX31091 Frequency Spreading Prole as a Function of Dither %
Figure 1. Center Dithered
TIME
1
DITHER FREQ
PROGRAMMED f
OUT
+
(1%, 2%, OR 4% OF f
OUT
)
PROGRAMMED f
OUT
-
(1%, 2%, OR 4% OF f
OUT
)
PROGRAMMED f
OUT
DITHER
AMOUNT
(±1%, ±2%,
OR ±4%)
IF DITHER AMOUNT = 0%
f
OUT
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Maxim Integrated
│
6
MAX31091 Automotive Temperature Range
Spread-Spectrum EconOscillator™
