[AK1541]
3. Fast Lockup Mode
Setting D[16] = {FASTEN} in <Address4> to “1” enables the Fast Lock Up mode for the AK1541.
Changing a frequency setting( The frequency is changed at the rising edge of [LE] when <Address1> and <Address2>
are accessed.) or [PDN2] pin is set ”Low” to ”High” with {FASTEN}=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) is enabled. After the timer period elapsed, the loop filter switch turns
OFF. The charge pump for normal operation (Charge Pump 1) is enabled..
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 x counter value set in {FAST[12:0]}
The charge pump current can be changed with the register setting in 16 steps in normal operation (Charge Pump 1) and 8
steps in the Fast Lockup operation (Charge Pump 2).
The charge pump current for normal operation (Charge Pump 1) is determined by the setting in {CP1[3:0]}, which is a 4-bit
address of D[18:15] in <Address2>, and a value of the resistance connected to the [BIAS] pin (19). The following formulas
show the relationship between the resistance value, the register setting and the electric current value.
Charge Pump 1 minimum current (CP1_min) = 0.285 / Resistance connected to the [BIAS] pin (19)
Charge Pump 1 current = CP1_min x (Charge Pump 1 setting + 1)
The charge pump current for the Fast Lockup mode operation (Charge Pump 2 current) is determined by the setting in
{CP2[2:0]}, which is a 3-bit address of D[15:13] in <Address4>, and a value of the resistance connected to the BIAS pin
The following formula show the relationship between the resistance value, the register setting and the electric current
value.
Charge Pump 2 minimum current (CP2_min) = 5.7 / Resistance connected to the [BIAS] pin
Charge Pump 2 minimum current (CP2_min) = CP2_min x (Charge Pump 2 setting + 4)
The allowed range value for the resistance (connected to the [BIAS] pin (19)) is from 33 to 22 [kΩ] for both normal and
Fast Lockup mode operations. For details of current settings, see ”10. Register Functional Description”.
First lockup time specified
by the timer
Operation mode
Charge pump
Normal
Charge pump 1
OFF
Fast Lockup Mode
Charge pump 2
ON
Normal
Charge pump 1
OFF
Lop filter switch
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
MS1043-E-05
13
2013/03
AKM [ ASAHI KASEI MICROSYSTEMS ]
