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TPS5430: TPS5430MDDAREP catch diode heating up

BOOM
Prodigy 95 points
Part Number: TPS5430

Team,

A strange catch diode heating issue is observed on one of our power boards. TPS5430MDDAREP as a buck converter to step down 12V to 3.3V in one of my designs. The catch diode used is B340A-13-F as recommended in the datasheet. The diode seems to get very hot when the device is turned on. The overall load on TPS is about 900mA. The temperature was observed using a thermal camera. Without any load connected, the diode is not heating up. Once we connect our other board, the diode starts heating. The diode starts heating even if we connect our second board with only 2 STM32 ICs (about 350mA). 

Also there is another TPS5430 used on the same board to generate 5V from 12V. That seems perfectly fine. 

D25 heating is the only issue. Rest works fine.

Inductor: L4 = SRP7050TA-150M by Bourns (15uH/3.5A)
Schottky diode: D25 = B340A-13-F by Diodes Incorporated
Sharing the schematics and layout snips. D25 is heating up. What could be the issue?
Schematic:
Top layer:
Bottom layer:
  • +1
    TI__Guru 64215 points

    Hello

    What temperature are you reading ?

    With your parameters, the average diode power is about 330mW.

    That gives a rise above ambient of about 46C, assuming 140C/W.

    Do the good and bad boards have the same amount of copper heat sink

    area connected to the diode ?

    Can you measure the PH node waveform with a 'scope so we can see if there 

    is anything strange going on.

    Thanks

  • 0 in reply to Frank De Stasi
    Prodigy 95 points

    The copper area is the same for both ICs. Layout considerations were taken care of. 

    The max read temperature on D25 was 42.4 deg C.

    Sharing the scope SS of PH node for both the ICs (3.3V and 5V generating TPS5430MDDAREP)

    1. Thermal camera image (with Load) == D25 temperature HIGH

    2. Thermal camera image (no Load) == D25 temperature normal

    3. PH pin of 3.3V TPS -- no Load

    4. PH pin of 3.3V TPS -- with Load

    5. 3.3V out

    ================================================================

    6. PH pin of 5V TPS - no load --- diode D30 not heating up

    7. PH pin of 5V TPS - with load --- diode D30 not heating up

    So is this normal? Any inputs on inductor current, loop gain and PH node ringing voltage?

  • 0 in reply to BOOM
    TI__Guru 64215 points

    Hello

    I think the diode temperature is OK.

    Your waveforms look OK.  The ringing you see is caused by DCM mode and is normal.

    It looks like the 'scope is having some issues triggering.

    Thanks