TPS63036 Start Up

Could you please repost the layout and schematic I am not able to see them?

What is the output current for your "high" load and "low" load condition? does this phenomena occurs in both load conditions?

Could you post scope plots, when this problem occurs? with Vin, Vout , EN, L1, L2 and if possible also the inductor current

Sabrina-
Thanks for your reply.

An additional occurrence of the TPS63036 fail to restart yielded V3R3 at 0.049 Volts and TPS63036 pin C1 at 0.116 Volts average.

Schematic:


Layout:


Four scope traces, with discussion following:

1) Enable and V3R3 with light load, Enable high success.

2) Enable and V3R3 with heavy load, Enable high success.

3) Enable and V3R3 with heavy load, Enable high FAILURE.

4) Enable Rise and TPS63036 pin B1,L1.

Discussion:
Load capacitance is approx. 30uF at TPS63036 plus another 20 uF 1.5 centimeters away.
Based on dV/dT and load capacitance, light load is about 26 mA, heavy load is 0.6 to 1.2 Amps.
Heavy load is only at fall of Enable and is not present at rise of Enable.
Figure 2) shows start up happens from about 2.2 volts. (Kind of like it has the  voltage elevation that my 1 volt blip did in my first posting.)
Figure 3) shows start up fails from 0.3 Volts.
The initial fall time of Fig 2) and Fig 3) appears (and I assume) are the same. Something appears to disconnect from the 30+20uF, leaving the 2.2 volts of
charge on that capacitance. I will investigate what is being disconnected.
Figure 4) Shows the TPS63036 is trying to start up but failing. Why? The TPS63036 data sheet indicates "no upper limit for the output capacitance". Start up into 50uF is our usual turn on where Vin and Enable rise together.

Thoughts?
Thanks
John

I did some measurements on the TPS63036 with a resistive and electronic load. I tried to reproduced this issue but as expected could not. What is your application? Regarding the output capacitance it should not be an issue. You can have higher output capacitance.

Regarding the layout, it looks OK but I would definitely rearrange the feedback resistive divider so that the output capacitors are placed the closest possible to the device. Do you have a separate layer for ground? I would also use more vias and polygon for the ground to have short ground connections.

 

I would like to clarify some points:

1. I see in this example  you have Vin=5V and Vout=3.3V. What is your whole input voltage range?

2. How/why did you choose this particular buck-boost  for your application?

3. For me it seems that the device is stuck in the short-circuit protection condition (please refer to chap. 7.4.1 of datasheet). When I look at the falling edge of the EN     The behavior of the VOUT trace is not the same on Fig.2 and Fig.3, Do you have the same load on both the conditions?  It seems to me that there is maybe somehow a load that consumes and prevents the Vout to raise.  It would be good to have Vin Vout and EN on the same scope plot. Could you guarantee you have the same load on both the conditions?

A bit more information:
Lengthening the on time to 450 mSec makes the turn off in the high load condition. My application takes about 330 msec to launch to high current. The 250 msec on time was running through the short 1 msec off time to get to the high current condition every other off time. Hence the bi-modal high and low load condtiion at turn off.

With the 450 msec on time, then lengthening the off time to 50 msec and the TPS63036 always start OK for 80,000 trials (figure 5 below). But why doesn't it always start with 1 msec off? My load is an RF amplifier with shut down. I'll examine the load and can substitute an equivalent resistor.

Layout comment: There is full ground flood, first layer down, with via in pad for all ground connections.

Re. 1: Full input voltage range is 3.0V to 5.5V. I think my previous load current estimate is a bit high. I hit the TPS63036 input currnet limit below 3.9 Volts Vin, but not at 5 Volts Vin.

Re. 2: Buck boost for operation down to 3.3 volts input, +/- 5% tolerance. The TPS63036 regulates to 3.4 volts, although I call it V3R3. We derate our allowed RF output power in deferecne to the input current limit that occurs for Vin below 3.9 Volts. (And would like a part with higher input current limit, but without any increase in size... or change in foot print or pin out.)

Re. 3: At time of turn off the loads are the same with the RF amplifier operational. As the voltage collapses the controlling processor sometimes has time to shut down the amplifier and the load current drops significantly as in figure 2, and sometimes thee processor doesn't get the chance, fig. 3. It depends on Where in the program loop this occurs and it would be nice not to have to mess with that. By the end of the 1 msec off the amplifier control is certainly in the off condition based on the fig. 3 V3R3 trace. But I'll investigate if the amplifier has some internal long delay that prevents it from shutting off. And, when I start from a Vin 0 to 5 volt rise after a prolonged off, the amp can't have been on, and I've seen the start up problem there. I'll examine amplifier load and equivalent resistance to verify amplifier on-off-ness.  Vin is near 5 Volts with slight I-R drop, never less than 4.5 volts, and basically looks like the Enable trace, only flat through the Enable low part.

Did your testing use rather short, i.e. 1 mSec, off times?

Figure 5. Enable and V3R3, Enable High 450 msec, Enable low 50 mSec, always works.

I would like to see the inductor current when this start-up failure event occurs.
And could you please make sure there is no high load condition (short circuit) from the load side?