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Device for under voltage protection/lock out/ cut off

Lucas Schulte9
Expert 6955 points
Other Parts Discussed in Thread: TLV809, TLV803, TPS3839, TPS3808, TLV810

Hello!

I am seeking a device that monitors Vcc and offers under voltage cut off or lock out. These are the only features I am interested in. I want to use this device in line with a separate device so that it would gate voltage to the separate device based on the under voltage threshold. Power for the system would be 5V at a maximum of 200ma. Is there such a device that does what I am looking for?

-Lucas Schulte

  • 0
    TI__Genius 12630 points

    Lucas,

    Yes we have plenty of devices that do exactly that. We call them Voltage Supervisors/Reset ICs. Since there are so many that do exactly what you requested, my next questions which will help me narrow which one you want more. Is cost, size, or low Iq your next biggest priority for your design? What delay do you want between the VCC coming back high to "good condition" and the output signaling "good condition/no undervoltage detected"? These next couple recommendations have a fixed 200ms delay between VCC coming back high and the output signaling "power good"

    Low cost: TLV803, TLV809 (these are the cheapest options available with the difference being open-drain output vs push-pull output)

    Small size and low Iq: TPS3839 (nano-power voltage supervisor and excellent choice for small size applications or battery powered application)

    If you need multi-channel, programmable delay, no delay at all, overvoltage monitoring, MCU processor monitoring via a Watchdog, or Manual Reset (the ability to reset the device or pull output low for any reason with external button or external signal) then let me know and we have devices for all of these as well.

    -Michael

  • 0 in reply to Michael_DeSando
    TI__Expert 6955 points
    Michael,

    At first glance it seems these devices monitor Vcc and sink current accordingly at the Reset pin. I could see this working in conjunction with a device that has an enable pin of some sort. Unfortunately, the device I am seeking to protect doesn't haveany kind of enable pin. I am looking for something that directly gates Vcc. I may be mistaken with my understanding of the Voltage Supervisors. Could the Reset pin, when paired with a resistor, be able to drive the gate of a FET that could in turn control power from Vcc?

    -Lucas
  • 0 in reply to Lucas Schulte9
    TI__Genius 12630 points
    Lucas,

    We have devices with ENABLE and MANUAL RESET (same functionality but different naming convention) so no need for any other device. And it sounds like you want an open-drain output that uses a pull-up resistor to the gate of the FET. I would argue it's possible to remove the external FET since the Voltage Supervisor already has an internal FET that is doing exactly what the external FET will do. And we have push-pull and open-drain (that requires a pull-up resistor) output types available and we have active-low (output is low when VCC is undervoltage) and active-high (output is high when VCC is undervoltage) output types available. The benefit of push-pull is low current consumption since there are two internal FETs turning on/off to either pull output to VCC or to GND. The open-drain output allows you to pull-up the output to any voltage regardless of VCC and allows for ORing together to create logic.

    These are for sure the devices you are looking for and I can help you choose the correct one. I would start with TPS3808 and see if that accomplishes your goal. If there is any block diagram or sensitive information you would like to provide me for detailed support, please email me directly at michaeldesando@ti.com

    -Michael
  • 0 in reply to Michael_DeSando
    TI__Expert 6955 points

    Michael,

    Unfortunately I still am not seeing how how the voltage supervisor alone meets my needs. I very well still may have a misunderstanding though. Yes i see these devices have a push-pull configuration for the Reset pin but I am also seeing that the Reset pin can only handle current less than 200ma. I am needing something that directly controls Vcc not just supervises and alerts accordingly. I will post some diagrams to further clarify my intentions.

    Typical Voltage Supervisor Application:

    Image result for tlv809

    This is the most common application I see with the voltage supervisors. The voltage supervisor is not directly controlling power from Vcc to the other device. It is only monitoring and alerting.

    What I need:

    Hope fully this clears things up. I apologize if I am still misunderstanding the capabilities of the voltage supervisors.

    -Lucas

  • 0 in reply to Lucas Schulte9
    TI__Expert 6955 points

    What I need: (original didn't populate)

  • 0 in reply to Lucas Schulte9
    TI__Expert 6955 points

    I apologize. e2e is not liking my image. I am now attaching it.

  • 0 in reply to Lucas Schulte9
    TI__Genius 12630 points

    Lucas,

    You are correct that you need an additional FET since your device requires 200mA. Please check this circuit that uses TLV810 (push-pull, active-high output) in addition to a p-FET to protect the next device.

    So if VCC is "high", the RST output will be "low" and the p-FET will be "on" and VCC will pass through to the Vin of protected device. If VCC is "low" then, RST output will be "high" and the p-FET will turn "off" and prevent any power to protected device.

    The "high" and "low" thresholds are defined by the device version of TLV810 you choose. We have 5V nominal supply rail options that I think work perfect for this exact application.

    -Michael

  • 0 in reply to Michael_DeSando
    TI__Expert 6955 points
    Michael,

    This is how I imagined the voltage supervisor working for my particular application. This would be a decent 2-component solution. Is there by chance a single component solution? Perhaps a different device in the line up of power devices?

    -Lucas
  • 0 in reply to Lucas Schulte9
    TI__Genius 12630 points
    Lucas,

    Unfortunately voltage supervisors are intended as control devices rather than power devices. If your device had an ENABLE pin then you would only need one device. You could also use one single voltage supervisor with an open-drain output type (with pull-up voltage high enough to power the protected device) but there will be significant voltage drop across the pull-up resistor for a 200mA application. For this case I believe the voltage supervisor with pass/protection p-FET is the best solution.

    -Michael
  • 0 in reply to Michael_DeSando
    TI__Expert 6955 points
    Michael,

    Thank you for your patience and advise. I will be considering this approach for problem I am trying to solve.

    -Lucas