Tool/software:
PostTo_TI_On_Blown_TPS25946EVM
I have a TPS25946EVM that does not appear to be functioning properly. It is not limiting the current. Prior to this happening a hard failure was observed. Smoke and a burning smell was noticed. Prior to this hard failure the EVM appeared to be functioning normally. It was limiting the current as expected and allowing current below the limit to pass. The blanking interval also appeared to function as expected.
This is what led up to the “smoke” event.
DC input of 12VDC applied between JP1/JP11
Jumper Settings:
- J3 default 1-2
- J4 default 3-4
- J5 5-6 for 18.3msec blanking
- J6 5-6 for 4.5A Current Limit
- J7 default 2-3
Did a test in the following sequence using a BK Precesion 8500 Electronic Load (EL):
- 0A 500msec
- 4A 500 msec
- 0A 500 msec
- 0A 500 msec
- 0A
Took a scope image identified as Test17.jpg
- Channel 1 yellow is output voltage across TP2/TP12
- Channel 2 purple is voltage across current sense resistor in low (minus) side
- Trigger was on channel 2 rising above 32 mV.
Then removed jumper at J5 to get minimium blanking. Power cycled the board. Reran above load sequence and saw smoke. Get scope image identified at Test18.jpg
After seeing the smoke ran more tests to determine what component may have failed. Did notice output cap C3 appears possibily damaged/distorted. See images C3_1.jpg – C3_3.jpg. Also board photos Board_1.jpg – Board_3.jpg
Now current limiting does not appear to work. With J6 set to 1-2 for 0.5A limit the board is allowing 1.0A load to pass thru as observed on the input power supply and electronic load. But the PG LED is lighting.
Scope Traces
- Reference non limited 0.5A load across sense resistor. Test22.jpg
- Reference non limited 1.0A load with J6 set to 3-4 for 2A limit. Test21.jpg
- J6 1-2 0.5A limit, EL set to 1A and outputing 1.0A
- Should be limited to 0.5A but not. PG LED on.
- jpg
- 1.jpg same trigger zoomed in. Cursors on Current
- 2.jpg same trigger zoomed in. Cursors on Output voltage
- jpg 1A load with J6 set to allow 2A. No limiting expected
- Scoping Itimer TP6 Channel 3 blue
- Voltage rises but expected it to drop as cap is discharged
- jpg powering on board
- jpg 1.0A load. J6 set for 0.5A limit. But not limited
- Scoping Itimer TP6 Channel 3 blue
- Voltage rises but expected it to drop as cap is discharged
- jpg Same as Test25.jpg zoomed out
- jpg Same as Test25 with not limited but expected
- Scoping BG TP9 Channel 3 blue
- jpg Same as Test25 with not limited but expected
- Scoping BGTH TP10 Channel 3 blue
- jpg Same as Test29 moved channel 3 for better view
Could cap C3 failing cause the eFuse to fail and not current limit?
