TPS54140: tps54140 startup issue

Sammi Shang

Part Number: TPS54140

Dear team,

TPS54140 has startup issue. We are not sure if it was caused by the input port. The 12V input is connected in series with 6 Ohm resistor with 100m network cable. 2 wires as VIN+, 2 wires as VIN-, 2 wires as VIN+.

The schematic:

The waveform: VIN-yellow; VOUT-blue.

Thanks.

Best regards,

Sammi

over 5 years ago

0 Iven Su over 5 years ago

TI__Expert 8245 points

Hi,

At which point you probe the Vin and Vout? Is Vin tested at start terminal of long wire or at device Vin and GND pins?

0 Sammi Shang over 5 years ago in reply to Iven Su

TI__Expert 4450 points

Hi Iven,

Thanks for your reply.

Customer test at the Vin pin of IC, I have not got the waveform at start terminal of long wire, but they are testing.

They found when add 3m~5m long wire, the startup is normal. The abnormal phenomenon happen with the wire length increase. Is the wire length will influence the IC startup?

Thanks.

Best regards,

Sammi

0 Iven Su over 5 years ago in reply to Sammi Shang

TI__Expert 8245 points

Hi,

If input voltage is tested at the Vin pin, it looks normal except the undershoot spike. Long wire has a large parasitic inductance so it's better to add a large E-cap (like 100uF) in the input to avoid instability.

0 Sammi Shang over 5 years ago in reply to Iven Su

TI__Expert 4450 points

Hi Iven,

Thanks for your reply. It became normal when add large E-cap when distance @50m. But still not stable when wire length is 100m, especially when load change. Could you kindly give some suggestion?

Thanks.

Best regards,

Sammi

0 Iven Su over 5 years ago in reply to Sammi Shang

TI__Expert 8245 points

Hi,

What's the E-cap value and where you add it?

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TPS54140: tps54140 startup issue