LMX2541SQE3740E/NOPB National Semiconductor, LMX2541SQE3740E/NOPB Datasheet - Page 52

• Manufacturer Part Number: LMX2541SQE3740E/NOPB
• Description: IC PLL FREQ SYNTH W/VCO 36LLP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Clock/Frequency Synthesizer (RF)r

Specifications of LMX2541SQE3740E/NOPB

• Pll: Yes
• Input: Clock
• Output: Clock
• Number Of Circuits: 1
• Ratio - Input:output: 2:2
• Differential - Input:output: No/No
• Frequency - Max: 4GHz
• Divider/multiplier: Yes/No
• Voltage - Supply: 3.15 V ~ 3.45 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-LLP
• Frequency-max: 4GHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LMX2541SQE3740ETR

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Single-Ended Operation
For differential operation, as is the case when using an LVDS
or LVPECL driver, a 100 Ω resistor is placed across the OS-
Cin/OSCin* traces
Differential Operation
A third way to configure the device is in crystal mode (XO =
1). For this, the crystal is placed across the OSCin/OSCin*
pins. Crystals are specified for a specific load capacitance,
C
value of C
Crystal Mode Operation
Load
. The load capacitors shown in the figure each have a
Load
/2.
30073325
30073323
30073324
52
3.2 CURRENT CONSUMPTION
The current consumption of the LMX2541 has many factors
that influence it. Determining the current consumption for the
entire device involves knowing which blocks are powered up
and adding their currents together. The current in the electri-
cal specifications gives some typical cases, but there could
be some variation over factors such as the phase detector
frequency. Also, the output buffer current can be impacted by
the software controllable settings. By subtracting or adding
combinations of the currents for the RFout buffer and VCO
divider, the current consumption for the device can be esti-
mated for any usable configuration. The currents for the buffer
and VCO divider are as follows:
3.3 FRACTIONAL SPURS
Primary Fractional Spurs
The primary fractional spurs occur at multiples of the channel
spacing and can change based on the fraction. For instance,
if the phase detector frequency is 10 MHz, and the channel
spacing is 100 kHz, then this could be achieved using a frac-
tion of 1/100. The fractional spurs would be at offsets that are
multiples 100 kHz.
Sub-Fractional Spurs
Sub-fractional spurs occur at sub-multiples of the channel
spacing, Fch. For instance, in the above example, there could
be a sub-fractional spur at 50 kHz. The occurrence of these
spurs is dependent on the modulator order. Integer mode and
the first order modulator never have sub-fractional spurs. If
the fractional denominator can be chosen to avoid factors of
2 or 3, then there will also be no sub-fractional spurs. Sub-
fractional spurs get worse for higher order modulators. Dither-
ing tends to reduce sub-fractional spurs at the expense of
increasing PLL phase noise. The following table provides
guidance on predicting sub-fractional spur offset frequencies.
RF Output Buffer
VCO Divider
Block
OUTPUT POWER WITH ON/
(See
3.7 PROGRAMMABLE
Current (mA)
OFF)
~ 40
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