ZHCSP40B October 2021 – June 2022 LMX2571-EP
PRODUCTION DATA
The LMX2571-EP includes a FastLock feature that can be used to improve the lock times in PLL mode when the loop bandwidth is small. In general, the lock time is approximately equal to 4 divided by the loop bandwidth. If the loop bandwidth is 1 kHz, then the lock time would be 4 ms. However, if the fPD is much higher than the loop bandwidth, cycle slipping may occur, and the actual lock time will be much longer. Traditional fastlock usually reduces lock time by increasing loop bandwidth during frequency switching. However, there is a limitation on the achievable maximum loop bandwidth due to limitation on charge-pump current and loop filter component values. In some cases, this kind of fastlock technique will make cycle slip even worse.
The LMX2571-EP adopts a new FastLock approach that eliminates the cycle slip problem. With an external analog SPST switch in conjunction with FastLock control of the LMX2571-EP, the lock time for a 100-MHz frequency switch could be settled in less than 1.5 ms. See Section 8.1.5 for details.