TPS54335A: Output pin (PH, pin 3) is shorted to GND

Hi, Zhang 

1. Could you send me the layout file for review? screenshot is okay. 

2. I found one error in schematic, the EN pin is low voltage pin, it is max rating voltage is 6V, but in your schematic, R30 and R34, R55 and R59 create 12V for EN pin. 

3. In your application, in the most of time, IC is working in light loading or heavy loading? 

Hi Ma:
1. layout follow below , if need file to review , please give me email address , thanks.

2.Yes,I found this error last time , and I already fix it.

3.In the most of time , IC is working in light loading.

-The IC(U5) heavy load(1~2A) when motor is operating , the operating time is 1~5 seconds.

-In this application , the IC(U6) output current 0.3~0.6 A in normal time.

Hi, Jingqing 

1. I found another error in your schematic, we cannot add C14 and C29 to RT pin which would cause loop unstable. 

So could you measure some waveforms at heavy/light loading? including Vout, PH signal. I want to check if loop is stable. 

2. Besides, I found the trace between IC's GND and input cap's GND is connected by VIAs, the loop area is big, when IC is switching, the PH node will have big spike voltage which might cause overstress on IC and damage IC. 

So could you measure the PH signal at max loading? I want to check the spike voltage on PH signal.  

1.In this application , C14 and C29 are open , it did not SMT electric capacity.

2.

(picture 1)U5's PH waveforms at light loading.

(picture 2)U5's PH waveforms at heavy loading.

(picture 3)U6's PH waveforms at normal time .

Hi, Zhang 

It looks there is big spike voltage on PH pin at light loading. 

1. Did you use the small loop to test PH signal? 

2. For the input voltage, is it well-regulated? what is the tolerance of input voltage? 

I concern Vin has big tolerance and plus spike voltage which is larger than maximum rating voltage of TPS54335A, then IC would be damaged. 

If you have re-design layout opportunity, suggest modify the layout according to the TPS54335A EVM reference design. 

https://www.ti.com/lit/ug/slvub76/slvub76.pdf?ts=1624849480277&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FTPS54335AEVM-010%253FkeyMatch%253D%2526tisearch%253Dsearch-everything%2526usecase%253Dpartmatches 

Dear Sir:

1.Are your mean that small loop between IC's GND and input cap's GND?

2. The input voltage's tolerance is ±2.5% (23.6V ~ 24.6V). 

Input power module datasheet link:

IRM-60-24 datasheet

Hi, Zhang 

1. Yes, see the small loop measurement in the below. 

And double check the spike voltage on PH voltage. 

2. It looks the Vin is well-regulated. 

However, still suggest modify the layout according to the EVM reference design. 

Dear Sir:

I follow the picture to measure the ph pin.Please help me to re-check the waveforms.

Hi,

Zhao will help on this later.

BRs,

Young

Hi, Zhang  

It looks the spike voltage on SW is not big. 

Right now, I also have no idea about why IC is damaged. 

Do you have the opportunity of modify the design? suggest changing to another IC TPS54302.   

Hi Zhao:

Is tps54335 existing some issue? In the using, has it some limit of using condition?

Hi, Zhang 

Very few customer reported the similar damage issue, maybe it is related with the application and PCB layout.