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TPS40170 EN pin damage

Matt Boland
Prodigy 250 points
Other Parts Discussed in Thread: TPS40170

I have used the TPS40170 in a design. I have made some prototypes and due to an overlay error, a cap and resistor were swapped. The end result was that the EN pin on the TPS40170 was left floating on some of my prototypes.  Now that I have swapped the resistor and cap, some start up, and some don't. Some start up and cannot be disabled with the EN pin. The datasheet says the EN pin must not be left floating. If it is, can damage to the IC occur so that the enable pin no longer works correctly, or at all? The power supply design is all OK and has been tested on earlier prototypes, this error was introduced on the latest round of prototypes.

  • 0
    TI__Mastermind 35165 points

    Hi Matt,

    Was it a resistor connected from VIN to EN which was populated with a cap instead of a resistor? If so, it's possible if VIN ramped quickly, some voltage was seen at the EN pin above the abs max damaging the EN pin. This will cause the EN pin to become damaged and non functional causing the TPS40170 to be unable to turn on.

    At the moment I'm not sure if only leaving the EN pin floating can cause damage to it, but it is a bad idea to do so because the voltage at the pin will then be unpredictable. It might be that if the pin is left floating, the EN pin is pulled above its abs max damaging it.

    Best Regards,
    Anthony

  • 0 in reply to Anthony F
    Prodigy 250 points

    Hi Anthony, no the EN pin was driven by a CMOS logic chip which had its OE# pin pulled up with a resistor. This OE pin had a capacitor put on it by mistake and the result was that internal leakage current was bring up the OE pin and then the CMOS was driving the EN pin on the TPS40170. I suspected some weren't behaving like this and thought that the EN pin may have been left floating in some cases. I did some testing by taking the CMOS OE pin high and low making the CMOS drive and then float the EN pin. I couldn't damage the EN pin by doing this, so I suspect the damage was caused by something else.