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TPS51120: Unable to apply correct logic level to enable input pins (EN2 and EN5)

Intellectual 435 points

Replies: 2

Views: 101

Part Number: TPS51120

Hi,

I have a 12V source, which I'm voltage dividing down to 4.4V, which is then connected to both EN2 and EN5. I've verified that 4.4V is present at the output of the voltage divider. However, when I connect the voltage divider output to the pin of EN5 (which is connected to EN2 via a trace), the voltage drops to ~0.78V. I initially thought there may have been some sporadic continuity issues, so I desoldered, checked everything and re-soldered, but I'm still getting the same ~0.78V at the EN2/5 pins. I've checked the Vin pin, which is seeing a stable 12V. Interestingly, I've changed the values of the voltage divider resistors, and despite now having a different input voltage, when the EN5 pin is connected, the voltage still drops down to 0.78-0.8V. This suggests to me that there may be some clamping or similar in place?

Any ideas as to what's going on here?

  • Hi,

    The enable pins are Hi-Z input pin. They should not sink lots of current. Have you tried to use a power supply connect directly to the EN pin? You may see how much current flowing into the pin on the power supply. 

    Regards,

    Hao

  • It looks like I've built the footprint for the TPS51120 in my EDA software upside down, so the 4.4V isn't actually interfacing with the EN pins after all!

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