Other Parts Discussed in Thread: LP5900, TPS720
Actual part # is LP5952TL-1.6/NOPB. The design I inherited uses two separate but dependent supplies. One for Vbatt and one for Vin. Both supplies come from a DC to DC convertor which produces 4V and 1.8V. The 1.8V goes directly to Vin of the LP5952. The 4V goes to an LP5900-3.3 LDO and then to Vbatt of the LP5952. We produce hundreds of these units and most work fine, but once in a while (reel related) we have units where a portion of the LP5952 LDOs fail. We believe the time delay of the LP5900 to produce the 3.3V for Vbatt may cause the failure we see sometimes. We have not as yet been able to prove it. Any thoughts about failure mechanism, margin of failure, and tolerance to failure when Vbatt is less than Vin, would be appreciated and especially tribal knowledge.
On a related issue; The datasheet for the LP5952, under the heading of “7.3.1 Dual-Rail Supply”, states (in two places) that “It is important that Vin does not exceed Vbatt at any time” (likely reason for above problem). However, in the datasheet under the heading of “6.1 Absolute Maximum Ratings”, there is a parameter stated; “BATT pin to IN pin: 0.2V max”. Does this mean the maximum voltage Vbatt can be above Vin is 0.2V (can’t be, device is designed to have a split of up to 4V (even a bit more), or does it mean that Vin can be above Vbatt 0.2, or finally does it mean that unless Vbatt is at least 0.2V above Vin the LDO is not guaranteed to output a voltage?
