TPS53318: TPS53318 shuts off under load

Hello John,

You are right, with Vin at 5.1V, Vout is 4.1V, with 6.3V Vin, Vout is exactly 5V.

To clarify:
With no load (only status LED) Vout is 5-5.1V for Vin 6.3 - 22V.
Below Vin 5.3V, Vout drops under load to about 3.5V, load higher than 1.4A shuts off output (not precise, tested with bunch of resistors), it recovers after load is removed.
Above Vin 5.3V any load shuts off output, it recovers after load is removed.
Above Vin 9.8V any load shuts out output, it does not recover until power cycle.

Below are screencaps with layout. I also attached pdf with assembly.

Assembly.PDFThanks,

Tomasz

No, it's not hot. Also, this shutdown happens instantly, I think that for thermal protection there would be some delay.

I suppose we will have to see some waveforms to determine what is actually happening.  We can start with Vout ans SW.  As usual it will probably take some time to troubleshoot over the forum.  If you observe any other waveforms which look suspicious, please include them.

Waveforms are included below.

SW: green
Vout: yellow

No load, Vin = 6.4V
scope_1

scope_2 (zoom of scope_1)

No load, Vin = 12V
scope_3

scope_4 (zoom of scope_3)

Shutdown, 0.2A load, Vin = 7V
scope_5

scope_6 (zoom of scope_5)

scope_7 (zoom of scope_5)

scope_8 (zoom of scope_5)

Shutdown, 0.2A load, Vin = 12V
scope_9

Thanks,

Tomasz

Can you zoom into pic 5 as shown in red?  Make sure the amplitude is such that I can see the full SW node amplitude and the time scale such that I can see and measure the on and off times.  You can take a couple at different time scales.  Just to be clear you have the supply up and operating at light or no load and then when you increase  the load current it drops out?  One thing you can quickly check is your ILIM component value and soldering connection.

Could you clarify, which part of scope_5 should I zoom into? I did not save this waveform, but can recreate a similar one. 

Yes, with no load/light load I have 5V output, which shuts off when I increase load.

I did solder another board today, this time with 100k RTRIP - output still shuts off. I did not find any shorts / cold joints on neither board.

Below are the waveforms you asked for.

Vin = 6.4V, Vout = 5V, tried 0.2A load

Thanks,

Tomasz

Below are VIN, VREG and Enable signals after adding load, there is definately voltage drop on VREG.

green: VIN
yellow: VREG
blue: enable

After VREG capacitor was changed to 4.7uF, shutdown happens at 6V Vin instead of 5.3V.
Tried with 100uF and 470uF cap at Vin, shutdown still occurs. Same with another regulated power supply and 12V/3A brick.

Thanks,
Tomasz

I have replaced resistor on voltage divider (R23=72k, instead 33k). Enable pin is now at over 2.5V (I will watch not to exceed 6V).
It did not fix the problem. However, I did notice that these voltage drops on VREG occur periodicaly.

I think that LDO should always be enabled if VIN is over 2V (8.3.1 - SLUSAY8E). Maybe these voltage drops are signs of LDO overcurrent?

green: VREG

yellow: enable

Thanks,

Tomasz

I've tested it, with enable pin pulled down VREG is still on.

Under load, VREG has periodic voltage drops (as shown in my last post). Maybe these drops trigger e.g. overvoltage protection?
As LDO is basically always on (above 2V), these drops could be caused by LDO overcurrent.

Screencaps in my last post were taken with 4.7uF capacitor on VREG.

I also tried different RF and MODE configurations - no significant changes.
Vout was lowered to ~4.8V (100k/15k).

Thanks,
Tomasz

I have two soldered boards, both have the same problem.

I have ordered more ICs, inductors (4.7u and 3.3u) and output capacitors (recommended by webench) from Farnell. I will solder another PCBs when these components arrive.

We plan to order 200 pcs as soon as possible, although I may make some layout changes if required.

Thanks,
Tomasz

Hello,

Is there any local capacitor at VDD pin (4.7uF). This VDD pin supplies the input to the VREG. Also, please tie ROVP to GND. Please see this section on the datasheet.

Yes, initially there was 1uF capacitor. I replaced it with 4.7u some time ago, it did not fix the problem.
ROVP has internal pulldown, but datasheet recommendeds connecting it to GND. I wired ROVP pin to GND, it did not help either.

I have soldered another PCB, this time using 3.3uH inductor (Wurth 744311330) and recommended output capacitors (2x 100uF GRM31CR60J107ME39L). Rtrip is maximum recommended 150k. Other components are the same as in schematic from my first post.

This new board works a bit better. Maximum Iout seems to depend on input voltage.
I was increasing Vin and noting down any interesting changes in Vout, Iout and input current (on power supply). Please see attached pdf.

Thanks,
TomaszTPS53318_vin_test.pdf

Hello,

TPS53318/9 released about 5 years ago and had been designed in many applications. So, the performance can not be just incremental better with increasing of number soldering the ICs on the same PCB layout.

I reviewed the schematic and verified with our excel design tool. It looks fine. I assumed that you are using TPS53318/9 on your PCB layout. Did you follow the PCB layout guideline on the datasheet? You can also populate and verify your schematic on TPS53318/9 EVM which is available on Digi-Key or ti.com website.  The PCB layout is very critical for the IC best performance.  Can you share your PCB layout so that we can help you to review?

I had seen the case of VREG sagging down when there is NO capacitor next to VDD pin.

In your report, you used resistor ladder for the load. Can you give more information on this kind of load (pictures, power loss capability)? Have you try to increase the load with electronic load?

Kit

Second board was soldered to check for bad solder joints or component failure. It behaves the same as first board (basically shuts off under any load).

Third board has different output capacitors and inductor, also TPS53318 is from different source. I works a bit better, the improvement was caused by using 3.3u inductor instead of 4.7u (I switched them back to confirm that).

Below is photo of my resistor setup.

Screenshots of PCB layout are attached in 3rd post of this topic. I cannot publish Altium project files here, but I can email them to you.

Do you suggest to replace components on TPS53319EVM-136 eval board (resistors, capacitors, inductor and TPS53319 for TPS53318) to check if problem is caused by layout of my PCB?

Thanks,
Tomasz