AK1546 Datasheet, PDF (13/39 Pages) Asahi Kasei Microsystems – 3GHz Low Noise Integer-N Frequency Synthesizer

[AK1546]
3. Fast Lock Up Mode
Setting {FAST[1:0]} in <Address2> to “11Bin” and {CPGAIN} in <Address1> to “1” enables the Fast Lock Up mode
for the AK1546.
The Fast Lock Up mode is enabled only during the time period set by the timer according to the counter value in
{TIMER[3:0]} in <Address2>. The charge pump current is set to the value specified by {CP2}. When the specified
time period elapses, the Fast Lock Up mode operation is switched to the normal operation, and {CPGAIN} in
<Address1> is reset to “0”.
{TIMER[3:0]} in <Address2> is used to set the time period for this mode. The following formula is used to calculate
the time period :
Switchover time = 1/F_PFD × Counter Value
Counter Value = 3 + (Timer[3:0] setting × 4)
Operation mode
Charge pump current
Loop filter Switch
Normal
Fast Lock Up time
specified by the timer
Fast Lock Up
CP1
CP2
OFF
ON
Normal
CP1
OFF
Frequency setting （Write “1” into {CPGAIN} in <Address1>.）
Fast Lock Up Mode Timing Chart
MS1388-E-00
13
2012/3