AK1573 Datasheet, PDF (32/42 Pages) Asahi Kasei Microsystems – Low Noise Integrated VCO

[AK1573/AK1573B/AK1573C]
13.3. Fast Lock-up mode
The AK1573 goes into Fast Lock Up mode by setting FASTEN bit in <Address0x04> to “1”. When A and
B counter setting is finished (writing in <Address0x01>), Fast Lock Up mode starts after calibration.
The Fast Lock Up mode is enabled only during the time period set by the timer according to the counter
value in FAST[3:0] bits in <Address0x04>. The charge pump current is set to the value specified by
CP2[2:0] bits. When the specified time period elapses, the Fast Lock Up mode operation is switched to
the normal operation, and the charge pump current returns to CP1[2:0] bits setting.
FAST[3:0] bits in <Address0x04> 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 + 4 × ( FAST[3:0] bits setting )
Operation mode
Normal
Calibration
Fast Lock Up time
specified by the timer
Fast Lock Up
Normal
Charge pump current CP1[2:0] bits
Hi-Z
CP2[2:0] bits
CP1[2:0] bits
Frequency setting (Write in <Address0x01>)
Figure.27 Fast Lock-up Mode Timing Chart
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