598AAA000107DG Silicon Labs, 598AAA000107DG Datasheet - Page 13

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598AAA000107DG

Manufacturer Part Number
598AAA000107DG
Description
Programmable Oscillators PRGRMMBL XO 8 PIN 0.5PS RS JTR
Manufacturer
Silicon Labs
Datasheet

Specifications of 598AAA000107DG

Product Category
Programmable Oscillators
Rohs
yes
Package / Case
7 mm x 5 mm
Frequency Stability
50 PPM
Supply Voltage
3.3 V
Termination Style
SMD/SMT
Output Format
LVPECL
Minimum Operating Temperature
- 40 C
Maximum Operating Temperature
+ 85 C
Dimensions
5 mm W x 7 mm L x 1.65 mm H
Mounting Style
SMD/SMT
Product
Programmable
A typical frequency configuration for this example:
RFREQ
F
F
Calculate RFREQ
from 148.35 to 148.5 MHz:
Note that performing calculations with RFREQ requires
a minimum of 38-bit arithmetic precision.
Relatively small changes in output frequency may
require writing more than one RFREQ register. Such
multi-register RFREQ writes can impact the output clock
frequency on a register-by-register basis during
updating.
Interim changes to the output clock during RFREQ
writes can be prevented by using the following
procedure:
1. Freeze the "M" value (Set Register 135 bit 5 = 1)
2. Write the new frequency configuration (RFREQ)
3. Unfreeze the "M" value (Set Register 135 bit 5 = 0)
3.1.2. Reconfiguring the Output Clock for Large
For output frequency changes outside of ±3500 ppm
from the center frequency, it is likely that both the DCO
frequency and the output dividers need to be
reprogrammed. Note that changing the DCO frequency
outside of the ±3500 ppm window will cause the output
to momentarily stop and restart at any arbitrary point in
a clock cycle. Devices sensitive to glitches or runt
pulses may have to be reset once reconfiguration is
complete.
The process for reconfiguring the output frequency
outside of a ±3500 ppm window is shown below:
1. Using the serial port, read the current values for
2. Calculate f
Once f
out_current
out_new
RFREQ, HSDIV, and N1.
slight variations of the internal crystal frequency from
one device to another, each device may have a
different RFREQ value or possibly even different
HSDIV or N1 values to maintain the same output
frequency. It is necessary to calculate f
device.
Changes in Output Frequency
RFREQ
XTAL
current
=
= 148.50 MHz
0x887B6473C
= 148.35 MHz
has been determined, new values for
XTAL
= 0x8858199E9
new
f
XTAL
new
=
for the device. Note that because of
0x8858199E9
=
to change the output frequency
F
-------------------------------------------------- -
out
RFREQ
HSDIV
148.50 MHz
------------------------------- -
148.35 MHz
N1
XTAL
for each
Rev. 1.0
RFREQ, HSDIV, and N1 are calculated to generate a
new output frequency (f
calculated manually or with the Si59x-EVB software,
which provides a user-friendly application to help find
the optimum values.
The first step in manually calculating the frequency
configuration is to determine new frequency divider
values (HSDIV, N1). Given the desired output frequency
(f
keep the DCO oscillation frequency in the range of 4.85
to 5.67 GHz.
Valid values of HSDIV are 9 or 11. N1 can be selected
as 1 or any even number up to 128 (i.e., 1, 2, 4, 6, 8, 10
… 128). To help minimize the device's power
consumption, the divider values should be selected to
keep the DCO's oscillation frequency as low as
possible. The lowest value of N1 with the highest value
of HS_DIV also results in the best power savings.
Once HS_DIV and N1 have been determined, the next
step is to calculate the reference frequency multiplier
(RFREQ).
RFREQ is programmable as a 38-bit binary fractional
frequency multiplier with the first 10 most significant bits
(MSBs) representing the integer portion of the multiplier
and the 28 least significant bits (LSBs) representing the
fractional portion.
Before entering a fractional number into the RFREQ
register, it must be converted to a 38-bit integer using a
bitwise left shift operation by 28 bits, which effectively
multiplies RFREQ by 2
Example:
RFREQ = 136.3441409d
Multiply RFREQ by 2
Discard the fractional portion = 36599601635d
Convert to hexadecimal = 0x8858199E9
Once the new values for RFREQ, HSDIV, and N1 are
determined, they can be written directly into the device
from the serial port using the following procedure:
1. Freeze the DCO (bit 4 of Register 137)
2. Write the new frequency configuration (RFREQ,
out_new
HS_DIV, N1)
), find the frequency divider values that will
f
DCO_new
RFREQ
=
f
out_new
28
28
= 36599601635.42d
new
.
out_new
=
HSDIV
Si598/Si599
f
---------------------- -
DCO_new
). New values can be
f
XTAL
new
N1
new
13

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