AK2400 Datasheet, PDF (36/52 Pages) Asahi Kasei Microsystems – High integrated receiver for PMR-LMR

[AK2400]
Charge Pump and Loop Filter (PLL SYNTHE)
AK2400 has two charge pumps; Charge Pump 1 for normal operation and Charge Pump 2 for Fast Lockup
mode. The internal timer is used to switch these two charge pumps to achieve a Fast Lock PLL.
The loop filter is external and connected to [CP], [SWIN] and [CPZ] pins. [CPZ] pin should be connected to
R2 and C2, which are intermediate nodes, even if the Fast Lockup is not used. Therefore, R2 must be
connected to [CP] pin, while C2 must be connected to the ground.
R2 and R2’ are connected in parallel with internal switch in Fast Lockup. These R2 and R2’ parallel
resistance value is required for calculating loop bandwidth and phase margin in Fast Lockup operation.
Phase Frequency
Detector
up
down
Timer
Loop Filter
CP
R3
C1 _R2'
R2
C3
on-resistance : 150
(for reference)
SWIN
C2
CPZ
Figure 14 Charge pump and Loop Filter
VCO
014008989-E-01
36
2015/4