Datasheet
ADF4360-2 Data Sheet
Rev. C | Page 16 of 24
POWER-UP
Power-Up Sequence
The correct programming sequence for the ADF4360-2 after
power-up is as:
1. R counter latch
2. Control latch
3. N counter latch
Initial Power-Up
Initial power-up refers to programming the part after the
application of voltage to the AV
DD
, DV
DD
, V
VCO
, and CE pins. On
initial power-up, an interval is required between programming
the control latch and programming the N counter latch.
This interval is necessary to allow the transient behavior of the
ADF4360-2 during initial power-up to have settled. During
initial power-up, a write to the control latch powers up the part
and the bias currents of the VCO begin to settle. If these
currents have not settled to within 10% of their steady-state
value, and if the N counter latch is then programmed, the VCO
may not be able to oscillate at the desired frequency, which does
not allow the band select logic to choose the correct frequency
band and the ADF4360-2 may not achieve lock. If the
recommended interval is inserted and the N counter latch is
programmed, the band select logic can choose the correct
frequency band, and the part locks to the correct frequency.
The duration of this interval is affected by the value of the
capacitor on the C
N
pin (Pin 14). This capacitor is used to
reduce the close-in noise of the ADF4360-2 VCO. The
recommended value of this capacitor is 10 µF. Using this value
requires an interval of ≥ 5 ms between the latching in of the
control latch bits and the latching in of the N counter latch bits.
If a shorter delay is required, this capacitor can be reduced. A
slight phase noise penalty is incurred by this change, which is
explained further in Tabl e 10.
Table 10. C
N
Capacitance vs. Interval and Phase Noise
C
N
Value Recommended Interval Between Control Latch and N Counter Latch Open-Loop Phase Noise @ 10 kHz Offset
10 µF ≥ 5 ms −86 dBc
440 nF ≥ 600 µs −85 dBc
CLOCK
POWER-UP
DATA
LE
R COUNTER
LATCH DATA
CONTROL
LATCH DATA
N COUNTER
LATCH DATA
REQUIRED INTERVAL
CONTROL LATCH WRITE TO
N COUNTER LATCH WRITE
04436-020
Figure 16. ADF4360-2 Power-Up Timing