TP5000 charging chip overheating when powering circuit on through switch - Page 1
Forum section: electronics / projects

author: fschuetz
author_rank: Newbie
timestamp: December 29, 2022, 12:27:40 pm
content: Hi allI am having a design where I use a TP5000 for charging a lifepo battery. The design can either be powered through the battery or usb-c plug. If both are present, the power will be taken from the usb using a p channel mosfet as simple power muxer. From the battery or USB, power is delivered over a sliding switch to two power curcuits around the TPS63020 to create a 5V and a 3.3V power rail (which then powers an esp32 some leds and some circuitry).There is a strange effect I cannot solve: The circuit works fine when the switch is in position on or off and the usb-c is plugged in. It also works fine when usb-c is plugged in while the switch is in position on and then flipped to off. However, when the usb-c is plugged in and the switch is in position off, but then flipped to on, the TP5000 start to rapidly overheat and unless the usb cable is removed within a second or two will release the magic smoke.My assumption is, that this is a dynamic issue, as static measurements did not reveal anything. One theory I came up with but could not verify is that the sudden power draw from the tps63020 and its caps when flicking the switch on trips the TP5000 somehow. I also tried taking a beefier inductor than in my original design as I suspected the 0805 package could reach its limit and go in resistive mode and trip the TP5000, but this did not change anything (replaced with a Sumida 0630CDMCCDS-6R8MC 6.8uH / 5A).Schema please see below. I also attach a image of the routing. It is a four layer pcb (signal-ground-power-signal) whereas red is top signal plane and green is bottom signal plane, the TP5000 is the chip 17 (top right). Does anyone have an idea why this overheating happens or some direction on what to analyse next? Any hints are greatly appreciated.Thank youFlorianTP5000 Datasheet:https://www.rlocman.ru/i/File/2019/12/03/1557926480137873.pdfTPS63020 Datasheet:https://www.ti.com/lit/ds/symlink/tps63020.pdfP-Channel Mosfet Datasheet:https://datasheet.lcsc.com/lcsc/2009211934_GOFORD-G16P03S_C840046.pdf

author: Ian.M
author_rank: Super Contributor
timestamp: December 29, 2022, 01:51:03 pm
content: Consider the inrush current of (presumably) ceramic capacitors C19 - C22, ringing with the USB lead self-inductance. Without the TP5000 and both TPS63020 present the voltage on your net 5V_SRC+ could peak at well over 11V (as ceramic capacitance decreases with increasing voltage, the peak of the ringing gets significantly intensified). With them present, it would seem that the TP5000 is the weak link even though its rated for 10V abs. max. supply voltage and the TPS63020 are only rated for 7V.You are already violating the USB inrush current specs, which require no more than 10uF on Vbus, so even if you clamp 5V_SRC+ or USB Vbus at under 7V, you may well experience issues if charging from a host port rather than a dedicated charger.Consider leaving the TPS63020 chips permanently connected and simply switching their enable pins between Vin and Gnd. With EN grounded they should each draw under 1uA. If there's any chance of the switch becoming unreliable, add a pulldown resistor for EN.

author: fschuetz
author_rank: Newbie
timestamp: January 03, 2023, 02:35:37 pm
content: Dear IanThanks for the quick reply. Sorry that it took me a while to answer, but I wanted to do some experiments with your suggestions first. I see that my design violates USB inrush current specs - thanks for pointing this out. I was not aware as I am new to PSU design. Am I correct, that due to the to high capacitance, to fulfil the spec I could limit the current during the first 100ms (after this, I should be good to draw up to 1.5A max - as set by the 5.1k resistors on the CC pins of the USB-C connection). Or how would I properly "isolate" the TPS63020 including its capacitors which are needed?Coming back to the overheating of the TPS5000: I did some more experiments, that suggest the inrush current might not be the problem for the overheating? All measurements are done with probe 1 (yellow) on V_BAT+ and probe 2 (turquoise) between the switch SW11 and the ferrite bead FB1.1) Switch on, no battery present, graphic 1 and 2: Plugging the connection in results in a ringing of around 340ms. Graphic 1 shows the details and graphic 2 shows the zoomed out view (same measurement). The ringing stabilises quickly. Peak voltage 11V. Voltage at V_BAT+ after plugging in is 3.6V, voltage between SW11 and FB1 is 5V --> as expected. TP5000 operating perfectly well.2) Switch off, no battery present, graphic 3,4: The ringing is measurable even if the switch is off. Cross talk, I assume? It can also be noticed, that the voltage peak is much smaller, which is to be expected as the caps are now disconnected. TP5000 working perfectly well.3) Switch off, no battery present, plugged in, graphic 5: This is what happens when we flip the switch from off to on, while plugged in. No ringing. Interestingly, V_BAT+ goes up to 5V and stays there. This is while the chip starts overheating. The TP5000 increases heat until after approximately 2 to 3 seconds it gets so hot it gets permanently damaged. If the plug is pulled fast enough, the chip cools down quickly. Not sure if the 5V are inflicted by the chip or come from somewhere else (see next point).4) Switch off, battery present, plugged in: Similar as before, but with a battery present. When flipping the switch on, the TP5000 starts to overheat. However, the voltage at V_BAT+ remains stable and does not increase to 5V. Unfortunately I forgot to screenshot this measurement. So no picture.I interpret this measurement such that while I must fix the design to comply with the inrush current specs, the capacitance is not the problem (ringing only when plugging in, overheating only when plugged in and switching from off to on and then no ringing). Also I should find out where the cross talk happens and fix this, but this might also not be the reason using the same logic as above? Thus think the overheating results from something else? A theory I discussed with colleagues would be that the internal logic of the TP5000 somehow becomes unstable and the internal FET turns on (100% duty cycle), but even if, what would cause this? Any idea or do you see the flaw in my thought process.Best,Florian

author: Ian.M
author_rank: Super Contributor
timestamp: January 03, 2023, 04:09:50 pm
content: It does seem something is triggering the TP5000 to latchup or enter a hard fault state. Your test #3 is interesting as it implies that it will do so on input transients irrespective of battery current. Scope screenshot #05 shows a large negative going transient or possibly ringing on channel 2 at switch-on. If that gets coupled to the TP5000 it could be the culprit, so I suggest doing further testing at the TP5000 Vin pin, preferably with minimum length probe ground springs rather than leads, to reduce the risk that the observed spikes are due to interactions via the probe ground leads inductance.