LMX2531LQ1570E/NOPB National Semiconductor, LMX2531LQ1570E/NOPB Datasheet - Page 5

• Manufacturer Part Number: LMX2531LQ1570E/NOPB
• Description: IC PLL FREQ SYNTH W/VCO 36-LLP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Clock/Frequency Synthesizer (RF)r

Specifications of LMX2531LQ1570E/NOPB

• Pll: Yes
• Input: Clock
• Output: CMOS
• Number Of Circuits: 1
• Ratio - Input:output: 2:2
• Differential - Input:output: No/No
• Frequency - Max: 1.636GHz
• Divider/multiplier: Yes/No
• Voltage - Supply: 2.8 V ~ 3.2 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-LLP
• Frequency-max: 1.6GHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LMX2531LQ1570ETR

VregPLL1
VregPLL2
VregVCO
VrefVCO
VregDIG There is not really any reason to use any other values than the recommended value of 10 nF
VccVCO
VccBUF
VccDIG
VccPLL
Connection Diagram
Pin(s)
DATA
CLK
LE
These pins are inputs to voltage regulators. Because the LMX2531 contains internal regulators, the power supply noise
rejection is very good and capacitors at this pin are not critical. An RC filter can be used to reduce supply noise, but if the
capacitor is too large and is placed too close to these pins, they can sometimes cause phase noise degradation in the 100
- 300 kHz offset range. Recommended values are from open to 1 μF. The series resistors serve to filter power supply noise
and isolate these pins from large capacitances.
If the VrefVCO capacitor is changed, it is recommended to keep this capacitor between 1/100 and 1/1000 of the value of
the VregVCO capacitor.
Because this pin is the output of a regulator, there are stability concerns if there is not sufficient series resistance. For
ceramic capacitors, the ESR (Equivalent Series Resistance) is too low, and it is recommended that a series resistance of
1 - 3.3Ω is necessary. If there is insufficient ESR, then there may be degradation in the phase noise, especially in the 100
- 300 kHz offset. Recommended values are from 1 μF to 10 μF.
The choice of the capacitor value at this pin involves a trade-off between integer spurs and phase noise in the 100 - 300
kHz offset range. Using a series resistor of about 220 mΩ in series with a capacitance that has an impedance of about 150
mΩ at the phase detector frequency seems to give an optimal trade-off. For instance, if the phase detector frequency is
2.5 MHz, then make this series capacitor 470 nF. If the phase detector frequency is 10 MHz, make this capacitance about
100 nF.
Since the maximum voltage on these pins is less than the minimum Vcc voltage, level shifting may be required if the output
voltage of the microcontroller is too high. This can be accomplished with a resistive divider.
Application Information
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