參數(shù)資料
型號: LMK04000BEVALXO
廠商: National Semiconductor
文件頁數(shù): 31/65頁
文件大?。?/td> 0K
描述: BOARD EVAL PREC CLOCK PLL XO
標(biāo)準(zhǔn)包裝: 1
系列: PowerWise®
主要目的: 計時,時鐘調(diào)節(jié)器
嵌入式:
已用 IC / 零件: LMK04000
主要屬性: 122.88 MHz 晶體
次要屬性: 集成式 PLL 和 VCO
已供物品: 板,線纜
SNOSAZ8J – SEPTEMBER 2008 – REVISED SEPTEMBER 2011
PLL1_R: PLL1_R Counter
The size of the PLL1_R counter is 12 bits. This counter will support a maximum divide ratio of 4095 and
minimum divide ratio of 1.
Table 17. PLL1_R Counter Values
R [11:0]
VALUE
b11
b10
b9
b8
b7
b6
b5
b4
b3
b2
b1
b0
0
Not Valid
0
1
.
...
1
4095
PLL1 Charge Pump Current Gain (PLL1_CP_GAIN) and Polarity Control (PLL1_CP_POL)
The Loop Band Width (LBW) on PLL1 should be narrow to suppress the noise from the system or input clocks at
CLKinX/CLKinX* port. This configuration allows the noise of the external VCXO to dominate at low offset
frequencies. Given that the noise of the external VCXO is far superior than the noise of PLL1, this setting
produces a very clean reference clock to PLL2 at the OSCin port.
In order to achieve a LBW as low as 10 Hz at the supported VCXO frequency (1 MHz to 200 MHz), a range of
charge pump currents in PLL1 is provided. The table below shows the available current gains. A small charge
pump current is required to obtain a narrow LBW at high phase detector rate (small N value).
Table 18. PLL1 Charge Pump Current Selections (PLL1_CP_GAIN)
PLL1_CP_GAIN [2:0]
PLL1 Charge Pump Current Magnitude (A)
b2
b1
b0
0
RESERVED
0
1
RESERVED
0
1
0
20
0
1
80
1
0
25
1
0
1
50
1
0
100
1
400
The PLL1_CP_POL bit sets the PLL1 charge pump for operation with a positive or negative slope VCO/VCXO. A
positive slope VCO/VCXO increases frequency with increased tuning voltage. A negative slope VCO/VCXO
increases frequency with decreased tuning voltage.
Table 19. PLL1 Charge Pump Polarity Control Bits (PLL1_CP_POL)
PLL1_CP_POL
DESCRIPTION
0
Negative Slope VCO/VCXO
1
Positive Slope VCO/VCXO
Register 13
EN_PLL2_XTAL: Crystal Oscillator Option Enable
If an external crystal is being used to implement a discrete VCXO, the internal feedback amplifier must be
enabled in order to complete the oscillator circuit.
Copyright 2008–2011, Texas Instruments Incorporated
37
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