TPS54540 Enable Pin

John Peters

Other Parts Discussed in Thread: TPS54540

Hi, I am currently using the TPS54540 with a 36V input and a 24V output. I have been having issues with the EN pin, specifically that it outputs a voltage (~6-8V). I want to enable the IC directly from a 5V source, but when they are connected together the voltage to the other circuit the 5V goes to rises. When the 5V source turns off and in turn is supposed to turn off the IC, the IC stays on. The 5V supply has a capacitor on it to keep the circuit going for a few seconds before shutting off completely, so my question is why is the enable pin being so stubborn? I managed to get the circuit to work by placing a diode in between so that current can only go from the 5V source to the enable.

Any help would be appreciated.

Thanks,

John

over 11 years ago

0 Anthony F over 11 years ago

TI__Mastermind 35165 points

Hi John,

Could you post a schematic of your circuit?

Thanks,
Anthony

0 John Peters over 11 years ago in reply to Anthony F

Prodigy 30 points

0 Anthony F over 11 years ago in reply to Anthony F

TI__Mastermind 35165 points

I will guess the behavior you want is that when the EN pin is floating the IC is disabled?

What is happening is the EN pin is capable of sourcing 6.3µA current max pulling it up to ~6 to 8V. You could put a resistor from the EN pin to ground that is small enough that the sourcing current doesn't pull the EN pin above the 1.1V minimum threshold. This means the resistor should be less than 174k.

0 John Peters over 11 years ago in reply to Anthony F

Prodigy 30 points

Just tried it and it sort of works, only issue is that the capacitor meant to keep the circuit on for a bit after drops voltage too fast.

Power management

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TPS54540 Enable Pin