This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS62743: Regulator intermittently goes into high current state when system turns on

Part Number: TPS62743
Other Parts Discussed in Thread: TPS22929D, TPS22860

We are experiencing strange behavior with this regulator when we initially turn on the power to our system. I'm happy to share our schematics privately, but I can't share them on this forum since our product is going into production soon.

It seems a similar issue was also reported in this follow post for this buck regulator.

Here is the behavior we've been observing:

We connect our system to a benchtop regulator set at 3.6V. For debugging purposes, our product will go into a powered down state immediately and we observe the current draw based off this sleep state. We expect a total current draw of about 600uA in this sleep state. With the benchtop regulator connected, we flip the switch to our system (its a PMOS switch connected to a mechanical switch, again, we can share schematics privately) and after the transients settle, we see a current draw of 1.8mA, way above what we expect. This behavior is reproducible and consistent.

We happened to do another test case, where we keep the switch of our product on, but power off the benchtop regulator itself. When we turn on the benchtop regulator (with the product's power switch already set to be on) we notice that the sleep current is about 550uA once transients settle. This is much better and about what we expect. This behavior is reproducible and consistent.

Based off this, we deduced that it must be an inrush current problem because the benchtop regulator probably slowly ramps its voltage up to 3.6V and therefore the inrush current is much less than when we flip the mechanical power switch of the product. With this assumption in mind, we tried the following solutions:

1) We currently have a 2.2uH inductor, 10uF output capacitor, and 47uF||10uF input capacitors. The inductor has a ESR of 78mOhms. I switched this inductor out for a 2.2uH indicator with an ESR of 155mOhms. Unfortunately this issue persisted. So we place the original 78mOhms inductor back in.

2) Increased the 47uF||10uF input capacitors. I've tried 10uF||10uF, 20uF||10uF, even 47uF||47uF but the issue persisted.

3) Tried adding various types of NTCs with different characteristics and initial resistances to reduce inrush current, but the issue still persisted and high current draw from the regulator got worst in some cases. 

4) Added capacitors/resistors to try and slow down the turn on time of our PMOS switching circuitry. Unfortunately this issue persisted and it could have been because I did not do it correctly. So I moved on to attempt #5

5) We bought the following TI load switches: TPS22860 and TPS22929D. We are assuming the the root cause of the TPS regulator high current draw is because of the inrush current putting the TPS regulator into some kind of high current draw state, we hoped that these load switches completely eliminate the inrush current problem. After replacing our original PMOS switching circuitry for our product with both of these load switches, we found that the issue STILL persisted! Which was pretty surprising. We even increased the input capacitor for both these load switches up to 47uF to slow down the voltage slew rate, but the issue still persisted.

So we are now hitting a wall. We assumed that the high current draw of the TPS regulator was being caused by some inrush current, but after trying to solve this with load switches and failing (which should have eliminated the inrush current) , we now believe that it might have to do with the design of the TPS buck regulator itself. Perhaps we are using wrong combinations of input capacitors, output capacitors, and inductors.

Any advice and feedback would be greatly appreciated!