Part Number: LMX2572
We are using the LMX2572 in a fast frequency hopping application, stepping through frequencies using full assist mode. We use a duty cycling with the CE pin of the chip to save power in between successive sweeps. We noticed that for several of our boards (but not all) the boards stop being able to lock frequency and transmit a signal at around 67C board temperature. This is a repeatable error that we can produce using a temperature chamber, and interestingly the chip can resume proper sweeping functionality as soon as the the board temperature below 67C.
In our debugging, we noticed that this failure occurs only after the CE pin is pulled low. If the CE pin is pulled low and then pulled high, VTUNE collapses to ~0V. However if the CE pin is kept high, sweeping still works as normal.
We also noted that if we use the chip's automatic per point VCO calibration, while at 67C the VTUNE does initally collapse to ~0V, it recovers with some delay. It alludes to some functionality in the chip's state machine that allows it to recover.
We have also been able to have full assist mode to work with LDO_DLY bit set to 0, but this is a setting not mentioned in the datasheet.
We would appreciate some advice one proper ways to resolve issue, as the ability to duty cycle the chip's power is very important to our application.
