Tool/software:
The TPS1685 on our board has been failing to output normally. We use a 24V input and have measured the voltages of the following pins:
SWEN (floating): 5V
MODE (floating): 4.6V
EN/UVLO: 4V
OVP: 0.77V
IREF: 1V
ILIM (grounded): 0V
It seems that neither the voltage protection nor the current protection has been triggered, but the output is only 1.8V, which makes it unable to work properly. Could you please provide some debugging directions or suggestions?
We have replaced a chip. Then, the output of the TPS16850 can reach 24V, but a new problem has emerged: The output voltage drops intermittently, falling from 24V to 6.8V, and then recovers after maintaining this low voltage for about 200 ms. This phenomenon usually recurs multiple times, and no pattern has been identified so far.
We tried turning off the DC-DC module and setting the load of TPS16850 to an open circuit, but similar issues still persist. The voltage shown in the diagram appears irregularly, just like in the previous tests with a load.
We have detected that the level of the FLT is frequently pulled low, each time lasting about 420ms, and the level of the SWEN is synchronized with it. During this process, the levels of the OVP, UNLO, and IMON remain within the normal range.
Could you please advise on what fault this might be, and are there any further detection methods available?
Sorry, due to limited conditions, the Iout cannot be tested, and the PG is also in a floating state. Therefore, three sets of waveforms have been measured.
VIN,VOUT,SWEN,FLT
VIN, VOUT, EN, OV
VIN,VOUT, IREF,IMON
The ILIM load is 1.3k, as mentioned previously. Currently, there is only one board, and more are expected to be produced next week. Layout is below, The FLT pin is connected to a voltage divider point on the board by flying wires.
