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參數(shù)資料
| 型號(hào)： | SK12430PJT |
| 元件分類： | 時(shí)鐘產(chǎn)生/分配 |
| 英文描述： | 800 MHz, OTHER CLOCK GENERATOR, PQCC28 |
| 封裝： | PLASTIC, LCC-28 |
| 文件頁(yè)數(shù)： | 14/16頁(yè) |
| 文件大?。?/td> | 225K |
| 代理商： | SK12430PJT |
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7
Revision 1/.ebruary 8, 2001
www.semtech.com
HIGH-PER.ORMANCE PRODUCTS
SK12430
ADVANCED
.unctional Block Diagram
Figure 4. Serial Test Clock Block Diagram
PLL 12429
M COUNTER
SHIFT
REG
14-BIT
0
1
N DIVIDE
(1, 2, 4, 8)
LATCH
Reset
FREF
S_CLOCK
S_DATA
S_LOAD
P_LOAD*
MCNT
VCO_CLK
DECODE
FDIV4
MCNT/2
LOW
FOUT
MCNT
MCNT/2
HIGH
7
0
SEL_CLK
T0
T1
T2
TEST
MUX
FOUT
(VIA ENABLE GATE)
TEST
T2 = T1 = 1, T0 = 0: Test Mode (PLL Bypass)
S_CLOCK is selected, MCNT/2 is on TEST output, S_CLOCK divide by N is on FOUT pin
P_LOAD* acts as reset for test pin latch. When latch reset, T2 data is shifted out of TEST pin.
Using the On-Board Crystal Oscillator
The SK12430 features a fully integrated on-board
crystal oscillator to minimize system implementation
costs.
The oscillator is a series resonant,
multivibrator type design as opposed to the more
common parallel resonant oscillator design. The se-
ries resonant design provides better stability and elimi-
nates the need for large on chip capacitors.
The
oscillator is totally self-
contained so
that the only external component re-
quired is the crystal.
As the oscillator is somewhat
sensitive to loading on its inputs the user is advised
to mount the crystal as close to the SK12430 as
possible to avoid any board level parasitics. To facili-
tate co-location surface mount crystals are recom-
mended, but not required.
The oscillator circuit is a series resonant circuit and
thus for optimum performance a series resonant crys-
tal should be used.
Unfortunately, most crystals
are characterized in a parallel resonant mode. For-
tunately, there is no physical difference between a
series resonant and a parallel resonant crystal. The
difference is purely in the way the devices are char-
acterized.
As a result, a parallel resonant crystal
can be used with the V with only a minor error in the
desired frequency. A parallel resonant mode crystal
used in a series resonant circuit will exhibit a
frequency of oscillation a few hundred ppm lower
than specified, a few hundred ppm translates to kHz
inaccuracies. In a general computer application, this
level of inaccurancy is immaterial
Table 1 below
specifies the performance requirements of the crys-
tals to be used with the SK12430.
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
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