AK1544 Datasheet, PDF (13/37 Pages) Asahi Kasei Microsystems – 1300MHz Integer-N Frequency Synthesizer

[AK1544]
3. Fast Lockup Mode
Setting D[16]={FSTEN} in <Address4> to 1 enables the Fast Lock Up mode for the AK1544.
Changing a frequency setting (The frequency is changed at the rising edge of [LE] when <Address1> is accessed.) or
[PDN2] pin is set to ”High” from ”High” with {FSTEN}=1 enables the Fast Lockup mode. The loop filter switch turns ON
during the timer period specified by the counter value in D[12:0] = {FAST[12:0]} in <Address4>, and the charge pump for
the Fast Lockup mode (Charge Pump 2) set by D[9:6]={CP2[3:0]} in <Address2> is enabled.
After the timer period elapsed, the loop filter switch turns OFF, the charge pump for normal operation (Charge Pump 1)
set by D[3:0]={CP1[3:0]} in <Address > is enabled and thus normal operation returns.
The register D[12:0]={FAST[12:0]} in <Address4> is used to set the timer period for this mode. The following formula is
used to calculate the time period:
Phase detector frequency cycle × counter value set in {FAST[12:0]}
The charge pump current could be adjusted with 9 steps for both normal operation (Charge Pump 1) and the Fast
Lockup operation (Charge Pump 2).
The absolute value of the charge pump current is determined by the resistance connected to the [BIAS] pin. The
following formula shows the relationship between the resistance value, the register setting and the electric current value.
Charge pump minimum current (Icp_min) [A] = 8.55 / Resistance connected to the [BIAS] pin ohm]
When CP1 or CP2 is 0000 to 0111, charge pump current [A] = Icp_min [A] x (CP1 or CP2 setting + 1)
When CP1 or CP2 is 1000, charge pump current [A] = Icp_min [A] / 2 (X is don’t care.)
The allowed range value for the resistance connected to the [BIAS] pin is from 22 to 33 [kΩ]. For details of current
settings, see ”Register Functional Description”.
Fast Lockup time specified
by the timer
Operation mode
Normal
Fast Lockup Mode
Normal
Charge pump
Charge pump 1
Charge pump 2
Charge pump 1
Lop filter switch
OFF
ON
OFF
The frequency is changed or [PDN2] pin is set ”Low” to ”High when D[16]={FSTEN}
in <Address4> is set to”1”.
Fig. 6 Timing Chart for Fast Lockup Mode
MS1350-E-01
13
2013/03