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AK2401 データシート(PDF) 42 Page - Asahi Kasei Microsystems |
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AK2401 データシート(HTML) 42 Page - Asahi Kasei Microsystems |
42 / 103 page [AK2401] 017003093-E-00 2017/3 42 13.7.4. Fast Lock Function Fast lock function of the AK2401 is enabled by setting FASTEN bit = “1” <Address 0x0C>. The timer of fast lock operation will start when accessing to the <Address 0x08> for changing the frequency. The loop filter switch is on for the timer period set by FAST_TIME[12:0] bits <Address 0x0D, 0x0E> and the charge pump current for fast lock function set by CPFAST[4:0] bits <Address 0x0B> is supplied. After the timer period is finished the loop filter switch is turned off and the normal charge pump current set by CPFINE[4:0] bits <Address 0x0A> is enabled. The timing chart of the fast lock function is shown Figure 25. The following formula is used to calculate the period of fast lock function. Timer Period = Phase Frequency Detector Frequency Cycle x FAST_TIME[12:0] bits The charge pump current is variable in 32 steps for both normal and fast lock operations. The charge pump current is determined by the resistance connected to the BIAS2 pin, CPFINE[4:0] bits <Address 0x0A> setting and CPFAST[4:0] bits <Address 0x0B> setting for normal and fast lock operations, respectively. The followings show the relationships between resistance, register settings and current. Minimum Current of Charge Pump (ICP_MIN) = 2.025 / resistor value [kΩ] of the BIAS2 pin Charge Pump Current [ μA] = I CP_MIN × (CPFINE[4:0] bit or CPFAST[4:0] bit + 1) The external resistor of the BIAS pin should be selected in the range of 22 ~ 33 k Ω. Refer to the CP in “15.5 <0x0A~0x0B>CP” for details of the setting. Fast Lockup Mode CPFAST ON Normal Operation Normal Operation CPFINE OFF CPFINE OFF Timer Period Normal Mode Charge Pump Loop Filter ON/OFF Switch Charge Pump current is changed on the timing writing to <Address0x08> if FSTEN bit is set to “1” <Address 0x0C>. Figure 25. Fast Lock Function Sequence |
同様の部品番号 - AK2401 |
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同様の説明 - AK2401 |
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