LMX2542LQ2121 NSC [National Semiconductor], LMX2542LQ2121 Datasheet - Page 12

• Manufacturer Part Number: LMX2542LQ2121
• Description: PLLatinum Cellular and GPS Frequency Synthesizer System with Integrated VCO
• Manufacturer: NSC [National Semiconductor]

www.national.com
1.0 Functional Description
1.2 VCO FREQUENCY TUNING
The center frequency of the RF VCO is determined mainly
by the resonant frequency of the tank circuit. This tank circuit
is implemented on-chip and requires no external inductor.
LMX2542 actively tunes the tank circuit to the required fre-
quency with the built-in tracking algorithm.
1.3 POWER CONTROL
LMX2542 includes a powerdown mode to reduce the power
consumption. LMX2542 can be powered down when the CE
pin is set LOW, independent of the state of the powerdown
bits. When CE is set HIGH, powerdown is controlled through
the MICROWIRE. The RF and IF circuitries are individually
powered down by setting the RF_EN (R1[3]) and IF_EN
(R2[2]) bits LOW respectively. Refer to Section 2.3.2 and
Section 2.4.1 for details on how to program the RF_EN and
IF_EN bits.
(Continued)
12
Note:
1. X refers to a don’t care condition.
2. The RF circuitry includes the whole RF synthesizer sys-
tem (synthesizer and VCO).
3. The IF circuitry includes the IF synthesizer block only.
CE Pin
0
1
1
1
1
RF_EN
X
0
0
1
1
IF_EN
X
0
1
0
1
Circuitry
OFF
OFF
OFF
ON
ON
RF
Circuitry
OFF
OFF
OFF
ON
ON
IF