AK1543 Datasheet, PDF (12/35 Pages) Asahi Kasei Microsystems – 1300MHz Delta-Sigma FractionalSigma -N Frequency Synthesizer

[AK1543]
2. Charge Pump and Loop Filter
The AK1543 has two charge pumps; Charge Pump 1 for normal operation and Charge Pump 2 for Fast Lockup.
The internal timer is used to switch those two charge pumps to achieve a fast lock PLL. The loop filter is external and
connected to [CP], [SWIN] and [CPZ] pins.
The [CPZ] pin should be connected to the R2 and C2 , which are intermediate nodes, even if the Fast Lockup is not used.
Therefore, R2 must be connected to the [CP] pin, while C2 must be connected to the ground.
Phase Detector
up
down
Timer
Loop Filter
CP
R3
C1 _R2'
R2
C3
VCO
SWIN
C2
CPZ
Fig. 5 Loop Filter Schematic
MS1206-E-02
12
2013/03