AK2400 Datasheet, PDF (37/52 Pages) Asahi Kasei Microsystems – High integrated receiver for PMR-LMR

[AK2400]
Fast lock-up mode (PLL SYNTH)
Setting D[16] = {FASTEN} in <Address4> to “1” enables the Fast Lock Up mode for the AK2400
Changing a frequency setting (The frequency is changed at the rising edge of [CSN], when <Address1> and
<Address2> are accessed.) or [PDSYNTH_N] pin is set from ”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 8 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[2:0]},
which is a 3-bit address of D[17:15] in <Address2>, and a value of the resistance connected to the BIAS3
pin. 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) = 0.57 / Resistance connected to the BIAS3 pin
Charge Pump 1 current = CP1_min × ({CP1[2:0]} + 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 BIAS3 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 BIAS3 pin
Charge Pump 2 minimum current (CP2_min) = CP2_min × ({CP2[2:0]} + 4)
The allowed range value for the resistance (connected to the BIAS3 pin (19)) is from 22 to 33 [kΩ] for both
normal and Fast Lockup mode operations.
First lockup time specified
by the timer
Operation
mode
Charge pump
Normal
Fast Lockup Mode
Charge pump 1
Charge pump 2
Normal
Charge pump 1
Lop filter switch
OFF
ON
OFF
The frequency is changed or {PDSYNTH_N} is set from ”Low” to ”High,
when D[16]={FSTEN} in < Address4 > is set to”1”.
Figure 15 Timing Chart for Fast Lockup Mode
014008989-E-01
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2015/4