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TLV3201: output mode when no Vcc

user4782171
Intellectual 1560 points
Part Number: TLV3201
Other Parts Discussed in Thread: TLV7011, TLV7021, TLV1805

Hi Team,

    Here need your help to have the suggestion for the application issue and circuit as attached.

    My customer uses TLV3201 for Over current sensing and face the issue that some parts will be low impedance and some parts will be high impedance under no Vcc supply condition (off mode). It looks the OP output is on uncertain mode. Can't control it would be high or low impedance mode when no Vcc applying. This  kind of high /low impedance behavior will follow the IC when do the OP SWAP checking. 

   My customer application needs to the output can keep high impedance when no Vcc applying condition. Does it mean that it needs to select open drain type for this kind of application or others?   

   Need your help to provide the circuit suggestion or suitable part but with the similar performance as TLV3201 for it.

OP Circuit.docx

Best regards,

Albert Lee.

  • 0
    TI__Mastermind 49986 points

    Hello Albert,

    What is the DVDD supply voltage?

    The problem is that you are using a push-pull output device, which will have a ESD clamp diode from the output to VCC. So when VCC is "off", the output pin is diode clamped to the VCC line. When the output voltage is higher than VCC, the VCC line will be back-fed through the ESD diode, pulling the VCC line up and effectively re-powering the comparator. This is probably why you are seeing different outputs.

    Cutting the VCC line to the comparator to "disable" is not a good idea.You are also continuously applying a voltage to the IN+ pin.

    It looks like they really want a open-drain type output. Some of these devices do not have clamps to VCC.

    Several of our newer comparators have internal POR circuitry so that the output is in a known condition when below minimum supply.

    See the TLV7011, TLV7021 or TLV1805, as these have POR circuitry with known start-up conditions.

    The TLV1805 output will be high impedance during the POR period, and also has a shutdown input (eliminates the need for the MOSFET).

    The TLV7021 is a open-drain output and will be "high impedance" when in the POR period, and does not have an output clamp. R1024 will act as the pull-up resistor.

  • 0 in reply to Paul Grohe
    TI__Intellectual 1560 points

    Hi Paul,

      Thanks your replying. DVDD is 3.3V.What I catch : My customer uses TLV3201 on PSE for output current limit circuit and cutting Vcc due to they would like to turn on PSE output first and then turn on the Vcc to supply TLV3201 (enable current limit after PSE out).

    Best regards,

    Albert Lee.

  • 0 in reply to user4782171
    TI__Mastermind 49986 points

    Hi Albert,

    An RC network could be added to the TLV1805 shutdown pin to delay it's startup reaction time. The TLV1805 is enabled when the SD pin is low. So it would need a pull-down resistor to GND and a cap from the SD pin to V+.