LTC6946
10
6946fa
PIN FUNCTIONS
VREFO+ (Pin 1): 3.15V to 3.45V Positive Supply Pin for
REFO Circuitry. This pin should be bypassed directly to
the ground plane using a 0.1μF ceramic capacitor as close
to the pin as possible.
REFO (Pin 2): Reference Frequency Output. This produces
a low noise square wave, buffered from the REF± differential
inputs. The output is self-biased and must be AC-coupled
with a 22nF capacitor.
STAT (Pin 3): Status Output. This signal is a configurable
logical OR combination of the UNLOK, LOK, ALCHI, ALCLO,
THI and TLO status bits, programmable via the STATUS
register. See the Operation section for more details.
CS (Pin 4): Serial Port Chip Select. This CMOS input initi-
ates a serial port communication burst when driven low,
ending the burst when driven back high. See the Operation
section for more details.
SCLK (Pin 5): Serial Port Clock. This CMOS input clocks
serial port input data on its rising edge. See the Operation
section for more details.
SDI (Pin 6): Serial Port Data Input. The serial port uses
this CMOS input for data. See the Operation section for
more details.
SDO (Pin 7): Serial Port Data Output. This CMOS three-
state output presents data from the serial port during a
read communication burst. Optionally attach a resistor
of >200k to GND to prevent a floating output. See the
Operation section for more details.
VD
+ (Pin 8): 3.15V to 3.45V Positive Supply Pin for Serial
Port Circuitry. This pin should be bypassed directly to the
ground plane using a 0.1μF ceramic capacitor as close to
the pin as possible.
MUTE (Pin 9): RF Mute. The CMOS active-low input mutes
the RF± differential outputs while maintaining internal bias
levels for quick response to de-assertion.
GND (Pins 10, 17, 21): Negative Power Supply (Ground).
These pins should be tied directly to the ground plane with
multiple vias for each pin.
RF–, RF+ (Pins 11, 12):
RF Output Signals. The VCO
output divider is buffered and presented differentially on
these pins. The outputs are open collector, with 136Ω
(typical) pull-up resistors tied to VRF+ to aid impedance
matching. If used single ended, the unused output should
be terminated to 50Ω. See the Applications Information
section for more details on impedance matching.