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TPS3808: Could you tell me about "TPS3808's negative voltage monitoring"?

Part Number: TPS3808
Other Parts Discussed in Thread: TL7700, UC1903, TPS386000

Hi, team.

I received a question from the customer "Can we respond to negative voltage monitoring on TPS3808?"
(The customer is considering of two ways.)

Can you tell me if it can be used?

(1) Connect the VDD pin to GND(0V),Connect the GND pin to the negative power supply(-5.0V).
Input to the SENSE pin is a value obtained by dividing GND negative power supply (about -4.5V:voltage value higher than the threshold value).
(The input voltage to the SENSE pin goes low as the negative power supply voltage drops)
Since GND is output to the output pin (RESET) at H and a negative power supply is output at L.
Received by a photocoupler or an operational amplifier, it is converted to the logic of the positive power supply and connected to the latter stage circuit.

This circuit is a track record using of TL7700 before.
(TL7700 can not be used because the board of this time is 105 ℃ specification)


(2) VDD pin connects positive power supply(5V) and GND pin to GND(0V).
For the SENSE pin, input a value obtained by dividing a positive power supply to a negative power supply (a voltage value lower than the threshold value).
When the negative supply causes a voltage drop, the input voltage to the SENSE pin goes high.
Since the output pin (RESET) becomes a logic inversion, connect the inverter to the subsequent stage circuit.

Best regards,

Masumi Sekiguchi.

  • Masumi Sekiguchi,

    Unfortunately the TPS3808 will not work. The internal circuitry prevents correct operation if you reverse the VDD and GND pin voltages.

    I'm also not sure TL7700 is meant to be used in the negative monitoring application although it may work. We can't guarantee the performance of our devices if you use them outside of the recommended operating specs.

    We have 4-channel devices with negative monitoring capability such as TPS386000 and UC1903.

    Can I ask more about this application? Why is negative voltage monitoring needed? We may be able to work out alternative solutions. Please email michaeldesando@ti.com if any of the information is sensitive.

    Please click “This resolved my issue” button if the answer provided resolved your issue.


    -Michael
  • Thank you for your reply.

    Do not seem to be transmitted, so let me explain in the diagram.

    The circuit configuration under consideration is as follows.

    Is it also usable with this configuration?

    The customer’s application can't tell me more information because confidential.

    But I can convey knowing me information as far as possible,

    it is described below.

    Useing With:Cockpit of aircraft

    Best regards,

    Masumi Sekiguchi

  • Masumi Sekiguchi,

    I attempted to replicate the circuits in the lab with no success. This configuration attempts to operate the device outside of the recommended operating specs. Especially for a safety-critical application such as aircraft, we can't guarantee the performance of our device operating outside of the recommended operating conditions. When I attempt to put 5V at GND pin and the 0V ground at VDD, the device doesn't behave as expected. Please share your results if you see something different.

    -Michael

  • Hi, Michael-san.

    It seems to be misunderstood, so I will correct as follows.

    >When I attempt to put 5V at GND pin and the 0V ground at VDD, the device doesn't behave as expected.
    ⇒Put -5V(negative voltage) at GND pin and the 0V ground at VDD.

     Is it still outside recommended operating range?

    Best regards,
    Masumi Sekiguchi
  • Masumi-san,

    All of the specs in the datasheet assume the GND pin is at 0V. I'm not sure it's possible to create a -5V potential at GND because GND is the 0V reference for the device. This is the same thing as 0V at GND and 5V at VDD. The internal circuitry uses internal references to turn on and off the internal FETs as necessary but the internal circuitry works assuming GND is 0V. For the device to operate correctly, GND should be 0V and VDD should be 1.7V to 6.5V. This device is not designed to operate with negative voltages.

    Please click “This resolved my issue” button if the answer provided resolved your issue

    -Michael

  • Thank you for the answer !

    That is, unless TPS386000 (or UC1903) is used,

    Is it OK that negative voltage detection can not be done by TI devices?

    Also, is it possible under the condition of "(2)"?

    Best regards,

    Masumi Sekiguchi

  • Masumi-san,

    Condition (2) still has 0V at VDD which is below the recommended minimum of 1.7V for correct device operation. We do have negative voltage monitoring devices, but we recommend using those devices rather than this device which is not specifically designed for negative voltage monitoring.

    Please let me know if you have any more questions! Please click “This resolved my issue” button if the answer provided resolved your issue.

    -Michael