AK1547 Datasheet, PDF (12/37 Pages) Asahi Kasei Microsystems – 4GHz Low Noise Integer-N Frequency Synthesizer

2．Charge Pump, Loop Filter
The current setting of charge pump can switch with the built-in timer for Fast Lock.
[AK1547]
Phase Detector
up
down
Timer
Loop Filter
CP
R3
C1
R2
C3
VCO
C2
Fig. 5 Loop Filter Schematic
The charge pump current for normal operation (CP1) is determined by the setting in {CP1[2:0]}, which is a 3-bit
address of {D[15:13]} in <Address2> and a value of the resistance connected to the [BIAS] pin. The charge pump
current for the Fast Lock Up mode operation (CP2) is determined by the setting in {CP2[2:0]}, which is a 3-bit
address of D[18:16] in <Address2> and a value of the resistance connected to the [BIAS] pin.
The following formula shows the relationship among the resistance value, the register setting and the electric
current value.
charge pump minimum current (Icp_min) [A] =17.46 / Resistance connected to the BIAS pin [Ω]
charge pump current (Icp) [A] = Icp_min [A] × ({CP1} or {CP2} setting +1)
The allowed value range for the resistance connected to the [BIAS] pin is from 22 to 33kΩ for both normal and
Fast Lock Up mode operations.
MS1464-E-00
12
2012/9