AK1545 Datasheet, PDF (13/39 Pages) Asahi Kasei Microsystems – 3.5GHz Low Noise Integer-N Frequency Synthesizer

[AK1545]
2．Charge Pump, Loop Filter and Fast Lock Up Mode
The current setting of charge pump and loop filter can switch with the built-in timer for Fast Lock.
Phase Detector
up
down
Timer
Loop Filter
CP
R3
C1
C2
C3
R2’
R2
SW
VCO
Fig. 5 Loop Filter Schematic
Fast Lock Mode 1
The output level of [SW] pin is programmed to a low state, and the charge pump current is switched to the
high value (1 mA). [SW] is used to switch a resistor in the loop filter and to ensure stability while in the fast
lock up mode by altering the loop bandwidth.
When the {CPGAIN} bit in the N register is set to “1”, the AK1545 enters the fast lock up mode. When the
{CPGAIN} bit in the N register is set to “0”, the AK1545 exits the fast lock up mode.
Fast Lock Mode 2
The output level of [SW] pin is programmed to a low state, and the charge pump current is switched to the
high value (1 mA). [SW] is used to switch a resistor in the loop filter and to ensure stability while in the fast
lock up mode by altering the loop bandwidth.
When the {CPGAIN} bit in the N register is set to “1”, the AK1545 enters the fast lock up mode. The AK1545
exits the fast lock up mode after the expiration of the timer. The timer configuration is set by the value in
{TIMER [3:0]}. After the timeout, the {CPGAIN} bit in the N register is automatically reset to 0, and the device
reverts to normal mode instead of the fast lock up mode.
MS1471-E-00
13
2012/10