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參數(shù)資料
| 型號： | MPC9892FA |
| 廠商： | MOTOROLA INC |
| 元件分類： | 時鐘及定時 |
| 英文描述： | PLL BASED CLOCK DRIVER, 5 TRUE OUTPUT(S), 0 INVERTED OUTPUT(S), PQFP32 |
| 封裝： | LQFP-32 |
| 文件頁數(shù)： | 5/5頁 |
| 文件大?。?/td> | 102K |
| 代理商： | MPC9892FA |
3
MPC9892
MOTOROLA ADVANCED CLOCK DRIVERS DEVICE DATA
310
APPLICATIONS INFORMATION
The MPC9892 is a dual clock PLL with on–chip Intelligent
Dynamic Clock Switch (IDCS) circuitry.
Definitions
primary clock: The input CLK selected by Sel_Clk.
secondary clock: The input CLK NOT selected by Sel_Clk.
PLL reference signal: The CLK selected as the PLL refer-
ence signal by Sel_Clk or IDCS. (IDCS can override Sel_Clk).
Status Functions
Clk_Selected: Clk_Selected (L) indicates CLK0 is selected as
the PLL reference signal. Clk_Selected (H) indicates CLK1 is
selected as the PLL reference signal.
INP_BAD: Latched (H) when it’s CLK is stuck (H) or (L) for at
least one Ext_FB period (Pos to Pos or Neg to Neg). Cleared
(L) on assertion of Alarm_Reset.
Control Functions
Sel_Clk: Sel_Clk (L) selects CLK0 as the primary clock.
Sel_Clk (H) selects CLK1 as the primary clock.
Alarm_Reset: Asserted by a negative edge. Generates a
one–shot reset pulse that clears INPUT_BAD latches and
Clk_Selected latch.
PLL_En: While (L), the PLL reference signal is substituted for
the VCO output.
MR: While (L), internal dividers are held in reset which holds all
Q outputs LOW.
Man Override (H)
(IDCS is disabled, PLL functions normally). PLL reference
signal (as indicated by Clk_Selected) will always be the CLK
selected by Sel_Clk. The status function INP_BAD is active in
Man Override (H) and (L).
Man Override (L)
(IDCS is enabled, PLL functions enhanced). The first CLK to
fail will latch it’s INP_BAD (H) status flag and select the other
input as the Clk_Selected for the PLL reference clock. Once
latched, the Clk_Selected and INP_BAD remain latched until
assertion of Alarm_Reset which clears all latches (INP_BADs
are cleared and Clk_Selected = Sel_Clk). NOTE: If both CLKs
are bad when Alarm_Reset is asserted, both INP_BADs will be
latched (H) after one Ext_FB period and Clk_Selected will be
latched (L) indicating CLK0 is the PLL reference signal. While
neither INP_BAD is latched (H), the Clk_Selected can be freely
changed with Sel_Clk. Whenever a CLK switch occurs,
(manually or by IDCS), following the next negative edge of the
newly selected PLL reference signal, the next positive edge pair
of Ext_FB and the newly selected PLL reference signal will slew
to alignment.
To calculate the overall uncertainty between the input CLKs
and the outputs from multiple MPC9892’s, the following
procedure should be used. Assuming that the input CLKs to all
MPC9892’s are exactly in phase, the total uncertainty will be the
sum of the static phase offset, max I/O jitter, and output to output
skew.
During a dynamic switch, the output phase between two
devices may be increased for a short period of time. If the two
input CLKs are 400ps out of phase, a dynamic switch of an
MPC9892 will result in an instantaneous phase change of
400ps to the PLL reference signal without a corresponding
change in the output phase (due to the limited response of the
PLL). As a result, the I/O phase of a device, undergoing this
switch, will initially be 400ps and diminish as the PLL slews to
its new phase alignment. This transient timing issue should be
considered when analyzing the overall skew budget of a
system.
Hot insertion and withdrawal
In PECL applications, a powered up driver will experience a
low impedance path through an MPC9892 input to its powered
down VCC pins. In this case, a 100 ohm series resistance
should be used in front of the input pins to limit the driver current.
The resistor will have minimal impact on the rise and fall times
of the input signals.
Acquiring Frequency Lock
1. While the MPC9892 is receiving a valid CLK signal, assert
Man_Override HIGH.
2. The PLL will phase and frequency lock within the specified
lock time.
3. Apply a HIGH to LOW transition to Alarm_Reset to reset
Input Bad flags.
4. De–assert Man_Override LOW to enable Intelligent Dynam-
ic Clock Switch mode.
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| MPC9893 | 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:Low Voltage PLL Intelligent Dynamic Clock (IDCS) Switch |
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