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TLV809E: Strange behaviour

Bart Hiddink
Prodigy 10 points
Part Number: TLV809E

Hi all,

I have a simple circuit with an issue.

The design is simple.

We have an input voltage of 2 to 4V and a TLV809EA29DCKR supervisor with push-pull output.

The output is directly connected to the gate of a FET, BSS214NWH6327XTSA1.

The problem is when I change the input voltage slowly from 2V to above above the threshold of the TLV (around 3V), the output of the TLV stays low (0.00V) and the FET won't switch.

I see the current pulsing with around 80uA every 200ms, so I assume the internal timer is trying to switch the output stage to high.

When I disconnect the gate of the FET, the TLV works fine.

When I connect the FET, the output of the TLV stays low.

What goes wrong?

ps. I've changed FETs and TLV's but it stays the same. Nothing is defect.

I've also tried a gate resistor if 47kOhm, but the output of the TLV stays low.

The output of the TLV goes finally high if I up the input voltage to 4.8V.

  • +1
    TI__Mastermind 19580 points

    Hi Bart,

    Can you add a cap on the VDD on the TLV809E and try these tests again?

  • +1
    Prodigy 10 points

    Hi Marcoo,

    That must be it.

    Off course the FET switches something and the source of this current is also coming from the same source.

    Assuming my power source is ideal is a big mistake.

    The input has a little 4.7ųF capacitor but this might be too small.

    I will take out my oscilloscope and look for proof.

    The hickup of the input current is a giveaway.

    When the TLV wants to switch on the voltage on the input drops again by the switched load. And so it keeps on triggering the output every 200ms for a very short period.

    Learning every day.

    Thanks for the hint.GrinningThumbsup

  • 0 in reply to Bart Hiddink
    Prodigy 10 points

    I've added 50uF to the source and increased the source drive strength to 250mA. The chip workes fine!