AK1548 Datasheet, PDF (14/42 Pages) Asahi Kasei Microsystems – 8GHz Low Noise Integer-N Frequency Synthesizer

[AK1548]
2．Charge Pump, Loop Filter
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
R2
C3
VCO
C2
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.
MS1364-E-00
14
2012/1