Part Number:LM5642
Hello,
One of our products uses a TI LM5642 dual-output switcher chip to convert a 12 V nominal battery bus to 3.3 V and 5 V buses. Our implementation of the chip is essentially the same as that shown in the LM5642 datasheet, except that the chip’s UV_DELAY pin is grounded (i.e., disabled). It appears that we have found a condition wherein the chip will latch its outputs into its under-voltage lockout (UVLO) state indefinitely, even though all of the chip’s inputs are thereafter in states consistent with normal operation.
The triggering event is a brief collapse and recovery of our battery bus, which is connected to pin 22 (VIN). For this condition, the LM5642 datasheet describesthe following behavior:
"When VIN falls to the chip’s UVLO threshold (i.e., ≈4.0 V), the chip’s shutdown sequence appears to execute as described above. If VIN remains below the threshold for at least ≈6 msec, the chip’s outputs will recover as described above when VIN is restored to its normal level (i.e., 12 V TYP). However, if VIN is held below the threshold for less than ≈6 msec before being restored to its normal level, the chip’s outputs fail to recover."
We’ve observed this phenomenon repeatedly in multiple units, so our current suspicion is that this behavior is intrinsic to the chip. We need to know whether or not this is the case, and which course of action we have to take to prevent it. What would you suggest?
Thanks in advance for your assistance,
Tim Starr on behalf of JR@ZM
