TPS2493EVM-002: IMON spurious output

Part Number: TPS2493EVM-002 I am evaluating the TSP2493 using the EVM-002 board. We plan to use the part with an MCU and monitor the output current, and use the UVEN line to control the output. During my testing, using the ENA/DIS switch on the PCB, I noted that sometimes the IMON output would go to full scale for about 200uS immediately after being enabled. To speed testing and eliminate any variables due to manual switching, I connected a signal generator to the UVEN line (see attached PDF). For this testing, no load was attached to the PCB. The only circuit elements present on VOUT are C3, C9 and D2 as indicated in the EVM schematic. What I then observed, is that depending on the PRF (repetition frequency), IMON either glitches, or does not glitch, immediately after UVEN goes high. For example, at 5.0Hz PRF, IMON behaves correctly when UVEN is asserted. At 5.1Hz, IMON goes full-scale for 200uS every time UVEN is asserted. I observed this behavior from as low as 0.7Hz, to as high as 20Hz, with variations in PRF from 0.01 to 0.1Hz causing a change in IMON behavior. There are 3 scope plots in the attached PDF. The two plots that show IMON indicate a small damped hump starting about 400uS after UVEN is asserted. This is the charging current of the capacitor(s) on VOUT. The third plot shows that VOUT has not begun to turn on yet when IMON goes full scale. All other signals (FAULT, PG, TIMER), maintain a steady value throughout the ON period. In other words, no other operation anomalies are observed, it seems that the IMON output is the only affected signal. TPS2493_IMON_Glitch.pdf Thanks for any insights, Will

Hi Will, Thanks for reaching out! We have never observed that kind of behavior. Can you capture Vout, input current, UVEN, IMON in a single scope shot for the second test scenario where IMON pulse is observed and share it with us Thanks, Rakesh

Thank you for the quick reply. I apologize that I do not have the appropriate test equipment to perform the measurement as requested. I have one additional piece of information which I dismissed but in retrospect may be important, and why you've never seen this. During my very initial tests, using just a power supply and active load, one of the two MOSFETS failed. It failed shorted Drain-Source (Gate/Source and Gate/Drain did not show a short). I desoldered the failed MOSFET, and have been testing since using the remaining MOSFET. The gate drive seems fine. I cannot explain what happened that cause the MOSFET to fail. It actually blew a blob of solder out from underneath it, when it heated quickly and then presumably failed. Part of the thermal pad appeared discolored... perhaps the part had a coating flaw or contamination causing lack of reflow to the land, and subsequent hot-spot. I assumed the TPS2493 was unaffected after this event, but perhaps whatever happened compromised the part somehow.

I should add that though I currently cannot capture 4 channels at once, the behavior I observe on the scope is very repeatable. For example Vout looks the same the entire time the PRF is set to cause the IMON glitch. How do you propose I measure the input current? I assume you mean a direct measurement using a current probe?

Hi Will, Thanks for the additional background details. Do you have another TSP2493 device to replace on EVM and to check whether the behavior is repeatable or not? By this, we can also rule out that partial unknown damage for the original unit is not the cause. If you have current probe, measure the input current along with the IMON voltage to check whether they follow in time Best Regards, Rakesh

Hi Rakesh, I will order a few new parts, or another EVM altogether, and report back. Continued testing shows everything else works as advertised (power limiting during startup, etc) Will

Hi Will, What are your target specs and requirements. ? Can you have a look at TPS25982, TPS1663x devices and let me know what you think. Regards, Rakesh

Hi Rakesh, Thanks for the recommendations. Based on our requirements, it doesn't appear either are suitable unfortunately. We are looking to run between 24-48V (surge to 50V), with up to 20A continuous current, with hardware-based fast transient overload protection, with slower MCU-based eFusing (i2t behavior). The application will have about 20 of these output channels, so keeping power dissipation low per channel is important for passive heat rejection which is also a requirement for us. I am looking at using the TPS2493 (or something equivalent) with an LM5050 ideal diode output in series (and a suitable TVS on the final output), with both controllers using NVMFS5C604NLWFAFT1G as the pass element. I am open to other topology or part number suggestions. This is what I've come up with after going through a previous design and prototype iteration, and new requirements being added (higher voltage, higher current, faster performance). Also perhaps worth mentioning, I am looking to protect the main power input using an LM5060 and 4x parallel of the above listed MOSFETs, to provide OVP shutdown and gross overcurrent protection, with 100A steady-state pass current. I just tested the LM5060 EVM and was happy with the performance. Thanks, Will

Hi Will, LM5069 would be preferred over LM5060 device. LM5069 provides accurate overload protection, FET SOA protection (power limiting feature) and fast shutdown during short circuit events. The LM5060 is intended for applications where precise current sensing is not required, but some level of fault protection is needed. Examples are applications where inductance or impedance in the power path limits the current rise in a short circuit condition. Please refer 8.1.5 Overcurrent Fault in the datasheet. Please refer <secret URL>/lit/an/snva683/snva683.pdf for configuring the device for surge support Best Regards, Rakesh

Hi Rakesh, I initially downselected to the 5060 vs the 5069 to eliminate the sense resistor, at the expense of a more uncontrolled current limit. I will re-evaluate based on your recommendation. Also, I have replacement TPS2493 parts coming, in addition to a new EVM. I will post results once they arrive and I can repeat the tests. Thanks Will

Hi Rakesh, Sorry for the delay in getting back. There was an issue getting the package delivered with the current state of affairs. The new EVM behaves with the same spurious IMON output. I will attach a PDF with a graph of all the parameters of interest. Since I do not have a good way to probe the input current, I inserted a 10 Ohm resistor in series with Vin, and the measurement Vin represents the power supply output, and Vin' represents the input voltage to the TPS2493EVM board. As in my original post, I can elicit this response by actuating the ENABLE switch on the PCB. For my testing, I connected a signal generator to UV(EN), adjusted the frequency until the problem arose, and then performed scope captures at each point in the circuit, at all times monitoring IMON to ensure the behavior was still present. TPS2493_EVM.pdf Also attached is the Excel file with the raw data I collected. TPS2493_EVM.xlsx Thank you for any insights, Will