
Pin Descriptions
Pin
Number
Pin Name
I/O Description
1
VccDIG
-
Power Supply for digital LDO circuitry. Input may range from 2.8 - 3.2 V. Bypass capacitors should be
placed as close as possible to this pin and ground.
Ground
3
GND
-
2,4,5,7,
12,
13,
29, 35
6
NC
-
No Connect.
VregBUF
-
Internally regulated voltage for the VCO buffer circuitry. Connect to ground with a capacitor.
MICROWIRE serial data input. High impedance CMOS input. This pin must not exceed 2.75V. Data is
clocked in MSB first. The last bits clocked in form the control or register select bits.
MICROWIRE clock input. High impedance CMOS input. This pin must not exceed 2.75V. Data is
clocked into the shift register on the rising edge.
MICROWIRE Latch Enable input. High impedance CMOS input. This pin must not exceed 2.75V.
Data stored in the shift register is loaded into the selected latch register when LE goes HIGH.
Chip Enable Input. High impedance CMOS input. This pin must not exceed 2.75V. When CE is
brought high the LMX2531 is powered up corresponding to the internal power control bits. It is
necessary to reprogram the R0 register to get the part to re-lock.
No Connect. Do NOT ground.
Power Supply for VCO regulator circuitry. Input may range from 2.8 - 3.2 V. Bypass capacitors should
be placed as close as possible to this pin and ground.
Internally regulated voltage for VCO circuitry. Not intended to drive an external load. Connect to
ground with a capacitor and some series resistance.
Internal reference voltage for VCO LDO. Not intended to drive an external load. Connect to ground
with a capacitor.
Ground for the VCO circuitry.
Ground for the RF Output Buffer circuitry.
O Buffered RF Output for the VCO.
Power Supply for the VCO Buffer circuitry. Input may range from 2.8 - 3.2 V. Bypass capacitors
should be placed as close as possible to this pin and ground.
Tuning voltage input for the VCO. For connection to the CPout Pin through an external passive loop
filter.
O Charge pump output for PLL. For connection to Vtune through an external passive loop filter.
O An open drain NMOS output which is used for FastLock or a general purpose output.
Internally regulated voltage for PLL charge pump. Not intended to drive an external load. Connect to
ground with a capacitor.
Power Supply for the PLL. Input may range from 2.8 - 3.2 V. Bypass capacitors should be placed as
close as possible to this pin and ground.
Internally regulated voltage for RF digital circuitry. Not intended to drive an external load. Connect to
ground with a capacitor.
O Multiplexed CMOS output. Typically used to monitor PLL lock condition.
I
Oscillator input. The oscillator can be placed in either single-ended or differential mode of operation.
Oscillator complimentary input. When a single ended source is used, then a bypass capacitor should
be placed as close as possible to this pin and be connected to ground.
O This pin if for test purposes and should be grounded for normal operation.
-
Ground
-
Internally regulated voltage for LDO digital circuitry.
8
DATA
I
9
CLK
I
10
LE
I
11
CE
I
14, 15
NC
-
16
VccVCO
-
17
VregVCO
-
18
VrefVCO
-
19
20
21
GND
GND
Fout
-
-
22
VccBUF
-
23
Vtune
I
24
25
CPout
FLout
26
VregPLL1
-
27
VccPLL
-
28
VregPLL2
-
30
31
Ftest/LD
OSCin
32
OSCin*
I
33
34
36
Test
GND
VregDIG
L
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